Lazy<T> Konstruktory

Definicja

Przestrzeń nazw:

System

Zestaw:

System.Runtime.dll

Inicjuje nowe wystąpienie klasy Lazy<T>.

Przeciążenia

Lazy<T>()	Inicjuje nowe wystąpienie klasy Lazy<T>. W przypadku wystąpienia opóźnionego inicjowania używany jest konstruktor bez parametrów typu docelowego.
Lazy<T>(Boolean)	Inicjuje nowe wystąpienie klasy Lazy<T>. Gdy wystąpi opóźnienie inicjowania, używany jest konstruktor bez parametrów typu docelowego i określony tryb inicjowania.
Lazy<T>(Func<T>)	Inicjuje nowe wystąpienie klasy Lazy<T>. Gdy wystąpi opóźnienie inicjowania, używana jest określona funkcja inicjowania.
Lazy<T>(LazyThreadSafetyMode)	Inicjuje nowe wystąpienie klasy Lazy<T>, która używa konstruktora bez parametrów T i określonego trybu bezpieczeństwa wątków.
Lazy<T>(T)	Inicjuje nowe wystąpienie klasy Lazy<T>, która używa wstępnie zdefiniowanej wartości.
Lazy<T>(Func<T>, Boolean)	Inicjuje nowe wystąpienie klasy Lazy<T>. Gdy wystąpi opóźnienie inicjowania, używana jest określona funkcja inicjowania i tryb inicjowania.
Lazy<T>(Func<T>, LazyThreadSafetyMode)	Inicjuje nowe wystąpienie klasy Lazy<T>, która używa określonej funkcji inicjowania i trybu bezpieczeństwa wątków.

Lazy<T>()

Źródło:

Lazy.cs

Inicjuje nowe wystąpienie klasy Lazy<T>. W przypadku wystąpienia opóźnionego inicjowania używany jest konstruktor bez parametrów typu docelowego.

public:
 Lazy();

public Lazy ();

Public Sub New ()

Przykłady

W poniższym przykładzie pokazano użycie tego konstruktora. Ilustruje również użycie konstruktora Lazy<T>(Boolean) (określając true dla isThreadSafe) i konstruktora Lazy<T>(LazyThreadSafetyMode) (określając LazyThreadSafetyMode.ExecutionAndPublication dla mode). Aby przełączyć się na inny konstruktor, po prostu zmień, które konstruktory są komentowane.

W przykładzie zdefiniowano klasę LargeObject, która zostanie zainicjowana z opóźnieniem przez jeden z kilku wątków. Dwa kluczowe wiersze kodu w tym przykładzie to tworzenie inicjatora i rzeczywiste inicjowanie. Na początku metody Main przykład tworzy bezpieczny wątkowo inicjator leniwy dla LargeObject:

lazyLargeObject = new Lazy<LargeObject>();

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//lazyLargeObject = new Lazy<LargeObject>(true);
//lazyLargeObject = new Lazy<LargeObject>(LazyThreadSafetyMode.ExecutionAndPublication);

let lazyLargeObject = Lazy<LargeObject>()

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//     let lazyLargeObject = Lazy<LargeObject>(true)
//     let lazyLargeObject = Lazy<LargeObject>(LazyThreadSafetyMode.ExecutionAndPublication)

lazyLargeObject = New Lazy(Of LargeObject)()

' The following lines show how to use other constructors to achieve exactly the
' same result as the previous line: 
'lazyLargeObject = New Lazy(Of LargeObject)(True)
'lazyLargeObject = New Lazy(Of LargeObject)(LazyThreadSafetyMode.ExecutionAndPublication)

W przykładzie są tworzone i uruchamiane trzy wątki, które blokują obiekt ManualResetEvent, dzięki czemu przykład może zwolnić wątki jednocześnie. Metoda ThreadProc używana przez wszystkie trzy wątki wywołuje właściwość Value w celu pobrania wystąpienia LargeObject:

LargeObject large = lazyLargeObject.Value;

let large = lazyLargeObject.Value

Dim large As LargeObject = lazyLargeObject.Value

Klasa Lazy<T> zapewnia blokowanie, dzięki czemu tylko jeden wątek może utworzyć wystąpienie LargeObject. W przykładzie pokazano, że wszystkie inne wątki uzyskują to samo wystąpienie.

Nuta

Dla uproszczenia w tym przykładzie użyto globalnego wystąpienia Lazy<T>, a wszystkie metody są static (Shared w Visual Basic). Nie są to wymagania dotyczące używania leniwej inicjalizacji.

using System;
using System.Threading;

class Program
{
    static Lazy<LargeObject> lazyLargeObject = null;

    static void Main()
    {
        // The lazy initializer is created here. LargeObject is not created until the
        // ThreadProc method executes.
        lazyLargeObject = new Lazy<LargeObject>();

        // The following lines show how to use other constructors to achieve exactly the
        // same result as the previous line:
        //lazyLargeObject = new Lazy<LargeObject>(true);
        //lazyLargeObject = new Lazy<LargeObject>(LazyThreadSafetyMode.ExecutionAndPublication);

        Console.WriteLine(
            "\r\nLargeObject is not created until you access the Value property of the lazy" +
            "\r\ninitializer. Press Enter to create LargeObject.");
        Console.ReadLine();

        // Create and start 3 threads, passing the same blocking event to all of them.
        ManualResetEvent startingGate = new ManualResetEvent(false);
        Thread[] threads = { new Thread(ThreadProc), new Thread(ThreadProc), new Thread(ThreadProc) };
        foreach (Thread t in threads)
        {
            t.Start(startingGate);
        }

        // Give all 3 threads time to start and wait, then release them all at once.
        Thread.Sleep(100);
        startingGate.Set();

        // Wait for all 3 threads to finish. (The order doesn't matter.)
        foreach (Thread t in threads)
        {
            t.Join();
        }

        Console.WriteLine("\r\nPress Enter to end the program");
        Console.ReadLine();
    }

    static void ThreadProc(object state)
    {
        // Wait for the signal.
        ManualResetEvent waitForStart = (ManualResetEvent) state;
        waitForStart.WaitOne();

        LargeObject large = lazyLargeObject.Value;

        // The following line introduces an artificial delay to exaggerate the race condition.
        Thread.Sleep(5);

        // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
        //            object after creation. You must lock the object before accessing it,
        //            unless the type is thread safe. (LargeObject is not thread safe.)
        lock(large)
        {
            large.Data[0] = Thread.CurrentThread.ManagedThreadId;
            Console.WriteLine("Initialized by thread {0}; last used by thread {1}.",
                large.InitializedBy, large.Data[0]);
        }
    }
}

class LargeObject
{
    int initBy = 0;
    public int InitializedBy { get { return initBy; } }

    public LargeObject()
    {
        initBy = Thread.CurrentThread.ManagedThreadId;
        Console.WriteLine("LargeObject was created on thread id {0}.", initBy);
    }
    public long[] Data = new long[100000000];
}

/* This example produces output similar to the following:

LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject.

LargeObject was created on thread id 4.
Initialized by thread 4; last used by thread 3.
Initialized by thread 4; last used by thread 4.
Initialized by thread 4; last used by thread 5.

Press Enter to end the program
 */

open System
open System.Threading

type LargeObject() =
    let initBy = Thread.CurrentThread.ManagedThreadId
    do
        printfn $"LargeObject was created on thread id {initBy}."

    member val Data = Array.zeroCreate<int64> 100000000 with get
    member _.InitializedBy = initBy

// The lazy initializer is created here. LargeObject is not created until the
// ThreadProc method executes.
let lazyLargeObject = Lazy<LargeObject>()

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//     let lazyLargeObject = Lazy<LargeObject>(true)
//     let lazyLargeObject = Lazy<LargeObject>(LazyThreadSafetyMode.ExecutionAndPublication)

let threadProc (state: obj) =
    // Wait for the signal.
    let waitForStart = state :?> ManualResetEvent
    waitForStart.WaitOne() |> ignore

    let large = lazyLargeObject.Value

    // The following line introduces an artificial delay to exaggerate the race condition.
    Thread.Sleep 5

    // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
    //            object after creation. You must lock the object before accessing it,
    //            unless the type is thread safe. (LargeObject is not thread safe.)
    lock large (fun () -> 
        large.Data[0] <- Thread.CurrentThread.ManagedThreadId
        printfn $"Initialized by thread {large.InitializedBy} last used by thread {large.Data[0]}." )

printfn """
LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject."""
stdin.ReadLine() |> ignore

// Create and start 3 threads, passing the same blocking event to all of them.
let startingGate = new ManualResetEvent false
let threads = [| Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc) |]
for t in threads do
    t.Start startingGate

// Give all 3 threads time to start and wait, then release them all at once.
Thread.Sleep 100
startingGate.Set() |> ignore

// Wait for all 3 threads to finish. (The order doesn't matter.)
for t in threads do
    t.Join()

printfn "\nPress Enter to end the program"
stdin.ReadLine() |> ignore

// This example produces output similar to the following:
//     LargeObject is not created until you access the Value property of the lazy
//     initializer. Press Enter to create LargeObject.
//    
//     LargeObject was created on thread id 4.
//     Initialized by thread 4 last used by thread 3.
//     Initialized by thread 4 last used by thread 4.
//     Initialized by thread 4 last used by thread 5.
//    
//     Press Enter to end the program

Imports System.Threading

Class Program
    Private Shared lazyLargeObject As Lazy(Of LargeObject) = Nothing

    Shared Sub Main()
        ' The lazy initializer is created here. LargeObject is not created until the 
        ' ThreadProc method executes.
        lazyLargeObject = New Lazy(Of LargeObject)()

        ' The following lines show how to use other constructors to achieve exactly the
        ' same result as the previous line: 
        'lazyLargeObject = New Lazy(Of LargeObject)(True)
        'lazyLargeObject = New Lazy(Of LargeObject)(LazyThreadSafetyMode.ExecutionAndPublication)


        Console.WriteLine( _
            vbCrLf & "LargeObject is not created until you access the Value property of the lazy" _
            & vbCrLf & "initializer. Press Enter to create LargeObject.")
        Console.ReadLine()

        ' Create and start 3 threads, passing the same blocking event to all of them.
        Dim startingGate As New ManualResetEvent(False)
        Dim threads() As Thread = { New Thread(AddressOf ThreadProc), 
            New Thread(AddressOf ThreadProc), New Thread(AddressOf ThreadProc) }
        For Each t As Thread In threads
            t.Start(startingGate)
        Next t

        ' Give all 3 threads time to start and wait, then release them all at once.
        Thread.Sleep(100)
        startingGate.Set()

        ' Wait for all 3 threads to finish. (The order doesn't matter.)
        For Each t As Thread In threads
            t.Join()
        Next t

        Console.WriteLine(vbCrLf & "Press Enter to end the program")
        Console.ReadLine()
    End Sub


    Private Shared Sub ThreadProc(ByVal state As Object)
        ' Wait for the signal.
        Dim waitForStart As ManualResetEvent = CType(state, ManualResetEvent)
        waitForStart.WaitOne()

        Dim large As LargeObject = lazyLargeObject.Value

        ' The following line introduces an artificial delay to exaggerate the race condition.
        Thread.Sleep(5)

        ' IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the  
        '            object after creation. You must lock the object before accessing it,
        '            unless the type is thread safe. (LargeObject is not thread safe.)
        SyncLock large
            large.Data(0) = Thread.CurrentThread.ManagedThreadId
            Console.WriteLine("Initialized by thread {0}; last used by thread {1}.", _
                large.InitializedBy, large.Data(0))
        End SyncLock
    End Sub
End Class

Class LargeObject
    Private initBy As Integer = 0
    Public ReadOnly Property InitializedBy() As Integer
        Get
            Return initBy
        End Get
    End Property

    Public Sub New()
        initBy = Thread.CurrentThread.ManagedThreadId
        Console.WriteLine("LargeObject was created on thread id {0}.", initBy)
    End Sub
    Public Data(100000000) As Long
End Class

' This example produces output similar to the following:
'
'LargeObject is not created until you access the Value property of the lazy
'initializer. Press Enter to create LargeObject.
'
'LargeObject was created on thread id 3.
'Initialized by thread 3; last used by thread 5.
'Initialized by thread 3; last used by thread 4.
'Initialized by thread 3; last used by thread 3.
'
'Press Enter to end the program

Uwagi

Wystąpienie utworzone za pomocą tego konstruktora może być używane współbieżnie z wielu wątków.

Tryb bezpieczeństwa wątku wystąpienia Lazy<T> zainicjowanego za pomocą tego konstruktora jest LazyThreadSafetyMode.ExecutionAndPublication. Tryb bezpieczeństwa wątku opisuje zachowanie, gdy wiele wątków próbuje zainicjować wystąpienie Lazy<T>.

Wystąpienie Lazy<T> utworzone za pomocą tego konstruktora nie buforuje wyjątków. Aby uzyskać więcej informacji, zobacz klasę Lazy<T> lub wyliczenie System.Threading.LazyThreadSafetyMode.

Zobacz też

• inicjowania z opóźnieniem

Lazy<T>(Boolean)

Źródło:

Lazy.cs

Inicjuje nowe wystąpienie klasy Lazy<T>. Gdy wystąpi opóźnienie inicjowania, używany jest konstruktor bez parametrów typu docelowego i określony tryb inicjowania.

public:
 Lazy(bool isThreadSafe);

public Lazy (bool isThreadSafe);

new Lazy<'T> : bool -> Lazy<'T>

Public Sub New (isThreadSafe As Boolean)

Parametry

isThreadSafe

Boolean

true, aby to wystąpienie było używane współbieżnie przez wiele wątków; false, aby wystąpienie było używane tylko przez jeden wątek naraz.

Przykłady

W poniższym przykładzie pokazano użycie tego konstruktora do utworzenia leniwego inicjatora, który nie jest bezpieczny wątkowo, w scenariuszach, w których cały dostęp do leniwie zainicjowanego obiektu występuje w tym samym wątku. Demonstruje również użycie konstruktora Lazy<T>(LazyThreadSafetyMode) (określając LazyThreadSafetyMode.None dla mode. Aby przełączyć się na inny konstruktor, po prostu zmień konstruktor, który jest skomentowany.

Nuta

Aby uzyskać kod, który pokazuje, jak używać tego konstruktora w scenariuszach wielowątkowym (określając true dla isThreadSafe), zobacz przykład konstruktora Lazy<T>().

W przykładzie zdefiniowano klasę LargeObject, która zostanie zainicjowana leniwie. W metodzie Main przykład tworzy wystąpienie Lazy<T>, a następnie wstrzymuje się. Po naciśnięciu Enter przykład uzyskuje dostęp do właściwości Value wystąpienia Lazy<T>, co powoduje wystąpienie inicjowania. Konstruktor klasy LargeObject wyświetla komunikat konsoli.

Nuta

Dla uproszczenia w tym przykładzie użyto globalnego wystąpienia Lazy<T>, a wszystkie metody są static (Shared w Visual Basic). Nie są to wymagania dotyczące używania leniwej inicjalizacji.

using System;
using System.Threading;

class Program
{
    static Lazy<LargeObject> lazyLargeObject = null;

    static void Main()
    {
        // The lazy initializer is created here. LargeObject is not created until the
        // ThreadProc method executes.
        lazyLargeObject = new Lazy<LargeObject>(false);

        // The following lines show how to use other constructors to achieve exactly the
        // same result as the previous line:
        //lazyLargeObject = new Lazy<LargeObject>(LazyThreadSafetyMode.None);

        Console.WriteLine(
            "\r\nLargeObject is not created until you access the Value property of the lazy" +
            "\r\ninitializer. Press Enter to create LargeObject.");
        Console.ReadLine();

        LargeObject large = lazyLargeObject.Value;

        large.Data[11] = 89;

        Console.WriteLine("\r\nPress Enter to end the program");
        Console.ReadLine();
    }
}

class LargeObject
{
    public LargeObject()
    {
        Console.WriteLine("LargeObject was created on thread id {0}.",
            Thread.CurrentThread.ManagedThreadId);
    }
    public long[] Data = new long[100000000];
}

/* This example produces output similar to the following:

LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject.

LargeObject was created on thread id 1.

Press Enter to end the program
 */

open System
open System.Threading

type LargeObject () =
    do
        printfn $"LargeObject was created on thread id {Thread.CurrentThread.ManagedThreadId}."

    member val Data = Array.zeroCreate<int64> 100000000 with get

// The lazy initializer is created here. LargeObject is not created until the
// ThreadProc method executes.
let lazyLargeObject = Lazy<LargeObject> false
// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//     let lazyLargeObject = Lazy<LargeObject>(LazyThreadSafetyMode.None)

printfn """
LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject."""
stdin.ReadLine() |> ignore

let large = lazyLargeObject.Value

large.Data[11] <- 89

printfn "\nPress Enter to end the program"
stdin.ReadLine() |> ignore


// This example produces output similar to the following:
//     LargeObject is not created until you access the Value property of the lazy
//     initializer. Press Enter to create LargeObject.
//     
//     LargeObject was created on thread id 1.
//     
//     Press Enter to end the program

Imports System.Threading

Friend Class Program
    Private Shared lazyLargeObject As Lazy(Of LargeObject) = Nothing

    Shared Sub Main()
        ' The lazy initializer is created here. LargeObject is not created until the 
        ' ThreadProc method executes.
        lazyLargeObject = New Lazy(Of LargeObject)(False)

        ' The following lines show how to use other constructors to achieve exactly the
        ' same result as the previous line: 
        'lazyLargeObject = new Lazy<LargeObject>(LazyThreadSafetyMode.None);


        Console.WriteLine( _
            vbCrLf & "LargeObject is not created until you access the Value property of the lazy" _
            & vbCrLf & "initializer. Press Enter to create LargeObject.")
        Console.ReadLine()

        Dim large As LargeObject = lazyLargeObject.Value

        large.Data(11) = 89

        Console.WriteLine(vbCrLf & "Press Enter to end the program")
        Console.ReadLine()
    End Sub
End Class

Friend Class LargeObject
    Public Sub New()
        Console.WriteLine("LargeObject was created on thread id {0}.", _
            Thread.CurrentThread.ManagedThreadId)
    End Sub
    Public Data(100000000) As Long
End Class

' This example produces output similar to the following:
'
'LargeObject is not created until you access the Value property of the lazy
'initializer. Press Enter to create LargeObject.
'
'LargeObject was created on thread id 1.
'
'Press Enter to end the program

Uwagi

Tryb bezpieczeństwa wątku wystąpienia Lazy<T> zainicjowanego za pomocą tego konstruktora jest LazyThreadSafetyMode.ExecutionAndPublication, jeśli isThreadSafe jest true; w przeciwnym razie tryb jest LazyThreadSafetyMode.None. Tryb bezpieczeństwa wątku opisuje zachowanie, gdy wiele wątków próbuje zainicjować wystąpienie Lazy<T>. Aby określić tryb LazyThreadSafetyMode.PublicationOnly, użyj konstruktora Lazy<T>(Func<T>, LazyThreadSafetyMode) lub Lazy<T>(LazyThreadSafetyMode).

Wystąpienie Lazy<T> utworzone za pomocą tego konstruktora nie buforuje wyjątków. Aby uzyskać więcej informacji, zobacz klasę Lazy<T> lub wyliczenie System.Threading.LazyThreadSafetyMode.

Zobacz też

• inicjowania z opóźnieniem

Lazy<T>(Func<T>)

Źródło:

Lazy.cs

Inicjuje nowe wystąpienie klasy Lazy<T>. Gdy wystąpi opóźnienie inicjowania, używana jest określona funkcja inicjowania.

public:
 Lazy(Func<T> ^ valueFactory);

public Lazy (Func<T> valueFactory);

new Lazy<'T> : Func<'T> -> Lazy<'T>

Public Sub New (valueFactory As Func(Of T))

Parametry

valueFactory

Func<T>

Delegat, który jest wywoływany w celu utworzenia leniwie zainicjowanej wartości, gdy jest potrzebny.

Wyjątki

ArgumentNullException

valueFactory jest null.

Przykłady

W poniższym przykładzie pokazano użycie tego konstruktora w celu zapewnienia opóźnionego inicjowania z buforowaniem wyjątków. Demonstruje również użycie konstruktora Lazy<T>(Func<T>, Boolean) (określając true dla isThreadSafe) i konstruktora Lazy<T>(Func<T>, LazyThreadSafetyMode) (określając LazyThreadSafetyMode.ExecutionAndPublication dla mode). Aby przełączyć się na inny konstruktor, po prostu zmień, które konstruktory są komentowane.

W przykładzie zdefiniowano klasę LargeObject, która zostanie zainicjowana z opóźnieniem przez jeden z kilku wątków. Trzy kluczowe sekcje kodu ilustrują tworzenie inicjatora, rzeczywiste inicjowanie i konstruktor klasy LargeObject, która demonstruje buforowanie wyjątków. Na początku metody Main przykład tworzy bezpieczny wątkowo inicjator leniwy dla LargeObject:

lazyLargeObject = new Lazy<LargeObject>(InitLargeObject);

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, true);
//lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, LazyThreadSafetyMode.ExecutionAndPublication);

let lazyLargeObject = Lazy<LargeObject> initLargeObject

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//     let lazyLargeObject = Lazy<LargeObject>(initLargeObject, true)
//     let lazyLargeObject = Lazy<LargeObject>(initLargeObject, LazyThreadSafetyMode.ExecutionAndPublication)

lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject)

' The following lines show how to use other constructors to achieve exactly the
' same result as the previous line: 
'lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, True)
'lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, LazyThreadSafetyMode.ExecutionAndPublication)

W przykładzie są tworzone i uruchamiane trzy wątki. Metoda ThreadProc używana przez wszystkie trzy wątki wywołuje właściwość Value w celu pobrania wystąpienia LargeObject:

try
{
    LargeObject large = lazyLargeObject.Value;

    // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
    //            object after creation. You must lock the object before accessing it,
    //            unless the type is thread safe. (LargeObject is not thread safe.)
    lock(large)
    {
        large.Data[0] = Thread.CurrentThread.ManagedThreadId;
        Console.WriteLine("Initialized by thread {0}; last used by thread {1}.",
            large.InitializedBy, large.Data[0]);
    }
}
catch (ApplicationException aex)
{
    Console.WriteLine("Exception: {0}", aex.Message);
}

try
    let large = lazyLargeObject.Value

    // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
    //            object after creation. You must lock the object before accessing it,
    //            unless the type is thread safe. (LargeObject is not thread safe.)
    lock large (fun () -> 
        large.Data[0] <- Thread.CurrentThread.ManagedThreadId
        printfn $"Initialized by thread {large.InitializedBy} last used by thread {large.Data[0]}.")
with :? ApplicationException as aex ->
    printfn $"Exception: {aex.Message}"

Try
    Dim large As LargeObject = lazyLargeObject.Value

    ' IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the  
    '            object after creation. You must lock the object before accessing it,
    '            unless the type is thread safe. (LargeObject is not thread safe.)
    SyncLock large
        large.Data(0) = Thread.CurrentThread.ManagedThreadId
        Console.WriteLine("Initialized by thread {0}; last used by thread {1}.", _
            large.InitializedBy, large.Data(0))
    End SyncLock
Catch aex As ApplicationException
    Console.WriteLine("Exception: {0}", aex.Message)
End Try

W konstruktorze klasy LargeObject trzecia sekcja klucza kodu zgłasza wyjątek przy pierwszym utworzeniu wystąpienia LargeObject, ale następnie umożliwia utworzenie wystąpienia:

static int instanceCount = 0;
public LargeObject()
{
    if (1 == Interlocked.Increment(ref instanceCount))
    {
        throw new ApplicationException("Throw only ONCE.");
    }

    initBy = Thread.CurrentThread.ManagedThreadId;
    Console.WriteLine("LargeObject was created on thread id {0}.", initBy);
}

type LargeObject() =
    static let mutable instanceCount = 0
    let initBy = Thread.CurrentThread.ManagedThreadId
    do
        if 1 = Interlocked.Increment &instanceCount then
            raise (ApplicationException "Throw only ONCE.")
        printfn $"LargeObject was created on thread id {initBy}."

Private Shared instanceCount As Integer = 0
Public Sub New()
    If 1 = Interlocked.Increment(instanceCount) Then
        Throw New ApplicationException("Throw only ONCE.")
    End If

    initBy = Thread.CurrentThread.ManagedThreadId
    Console.WriteLine("LargeObject was created on thread id {0}.", initBy)
End Sub

Po uruchomieniu przykładu pierwszy wątek, który próbuje utworzyć wystąpienie LargeObject kończy się niepowodzeniem, a wyjątek zostanie przechwycony. Można oczekiwać, że następny wątek pomyślnie utworzy wystąpienie, ale obiekt Lazy<T> buforował wyjątek. W związku z tym wszystkie trzy wątki zgłaszają wyjątek.

Nuta

Dla uproszczenia w tym przykładzie użyto globalnego wystąpienia Lazy<T>, a wszystkie metody są static (Shared w Visual Basic). Nie są to wymagania dotyczące używania leniwej inicjalizacji.

using System;
using System.Threading;

class Program
{
    static Lazy<LargeObject> lazyLargeObject = null;

    static LargeObject InitLargeObject()
    {
        return new LargeObject();
    }

    static void Main()
    {
        // The lazy initializer is created here. LargeObject is not created until the
        // ThreadProc method executes.
        lazyLargeObject = new Lazy<LargeObject>(InitLargeObject);

        // The following lines show how to use other constructors to achieve exactly the
        // same result as the previous line:
        //lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, true);
        //lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, LazyThreadSafetyMode.ExecutionAndPublication);

        Console.WriteLine(
            "\r\nLargeObject is not created until you access the Value property of the lazy" +
            "\r\ninitializer. Press Enter to create LargeObject.");
        Console.ReadLine();

        // Create and start 3 threads, each of which tries to use LargeObject.
        Thread[] threads = { new Thread(ThreadProc), new Thread(ThreadProc), new Thread(ThreadProc) };
        foreach (Thread t in threads)
        {
            t.Start();
        }

        // Wait for all 3 threads to finish. (The order doesn't matter.)
        foreach (Thread t in threads)
        {
            t.Join();
        }

        Console.WriteLine("\r\nPress Enter to end the program");
        Console.ReadLine();
    }

    static void ThreadProc(object state)
    {
        try
        {
            LargeObject large = lazyLargeObject.Value;

            // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
            //            object after creation. You must lock the object before accessing it,
            //            unless the type is thread safe. (LargeObject is not thread safe.)
            lock(large)
            {
                large.Data[0] = Thread.CurrentThread.ManagedThreadId;
                Console.WriteLine("Initialized by thread {0}; last used by thread {1}.",
                    large.InitializedBy, large.Data[0]);
            }
        }
        catch (ApplicationException aex)
        {
            Console.WriteLine("Exception: {0}", aex.Message);
        }
    }
}

class LargeObject
{
    int initBy = 0;
    public int InitializedBy { get { return initBy; } }

    static int instanceCount = 0;
    public LargeObject()
    {
        if (1 == Interlocked.Increment(ref instanceCount))
        {
            throw new ApplicationException("Throw only ONCE.");
        }

        initBy = Thread.CurrentThread.ManagedThreadId;
        Console.WriteLine("LargeObject was created on thread id {0}.", initBy);
    }
    public long[] Data = new long[100000000];
}

/* This example produces output similar to the following:

LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject.

Exception: Throw only ONCE.
Exception: Throw only ONCE.
Exception: Throw only ONCE.

Press Enter to end the program
 */

open System
open System.Threading

type LargeObject() =
    static let mutable instanceCount = 0
    let initBy = Thread.CurrentThread.ManagedThreadId
    do
        if 1 = Interlocked.Increment &instanceCount then
            raise (ApplicationException "Throw only ONCE.")
        printfn $"LargeObject was created on thread id {initBy}."
    member _.InitializedBy = initBy
    member val Data = Array.zeroCreate<int64> 100000000

let initLargeObject () =
    LargeObject()

// The lazy initializer is created here. LargeObject is not created until the
// ThreadProc method executes.
let lazyLargeObject = Lazy<LargeObject> initLargeObject

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//     let lazyLargeObject = Lazy<LargeObject>(initLargeObject, true)
//     let lazyLargeObject = Lazy<LargeObject>(initLargeObject, LazyThreadSafetyMode.ExecutionAndPublication)

let threadProc _ =
    try
        let large = lazyLargeObject.Value

        // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
        //            object after creation. You must lock the object before accessing it,
        //            unless the type is thread safe. (LargeObject is not thread safe.)
        lock large (fun () -> 
            large.Data[0] <- Thread.CurrentThread.ManagedThreadId
            printfn $"Initialized by thread {large.InitializedBy} last used by thread {large.Data[0]}.")
    with :? ApplicationException as aex ->
        printfn $"Exception: {aex.Message}"

printfn """
LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject."""
stdin.ReadLine () |> ignore

// Create and start 3 threads, each of which tries to use LargeObject.
let threads = 
    [| Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc) |]
for t in threads do
    t.Start()

// Wait for all 3 threads to finish. (The order doesn't matter.)
for t in threads do
    t.Join()

printfn "\nPress Enter to end the program"
stdin.ReadLine() |> ignore

// This example produces output similar to the following:
//     LargeObject is not created until you access the Value property of the lazy
//     initializer. Press Enter to create LargeObject.
//     
//     Exception: Throw only ONCE.
//     Exception: Throw only ONCE.
//     Exception: Throw only ONCE.
//     
//     Press Enter to end the program

Imports System.Threading

Friend Class Program
    Private Shared lazyLargeObject As Lazy(Of LargeObject) = Nothing

    Private Shared Function InitLargeObject() As LargeObject
        Return New LargeObject()
    End Function


    Shared Sub Main()
        ' The lazy initializer is created here. LargeObject is not created until the 
        ' ThreadProc method executes.
        lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject)

        ' The following lines show how to use other constructors to achieve exactly the
        ' same result as the previous line: 
        'lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, True)
        'lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, LazyThreadSafetyMode.ExecutionAndPublication)


        Console.WriteLine(vbCrLf _
            & "LargeObject is not created until you access the Value property of the lazy" _
            & vbCrLf & "initializer. Press Enter to create LargeObject.")
        Console.ReadLine()

        ' Create and start 3 threads, each of which tries to use LargeObject.
        Dim threads() As Thread = { New Thread(AddressOf ThreadProc), _
            New Thread(AddressOf ThreadProc), New Thread(AddressOf ThreadProc) }
        For Each t As Thread In threads
            t.Start()
        Next t

        ' Wait for all 3 threads to finish. (The order doesn't matter.)
        For Each t As Thread In threads
            t.Join()
        Next t

        Console.WriteLine(vbCrLf & "Press Enter to end the program")
        Console.ReadLine()
    End Sub


    Private Shared Sub ThreadProc(ByVal state As Object)
        Try
            Dim large As LargeObject = lazyLargeObject.Value

            ' IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the  
            '            object after creation. You must lock the object before accessing it,
            '            unless the type is thread safe. (LargeObject is not thread safe.)
            SyncLock large
                large.Data(0) = Thread.CurrentThread.ManagedThreadId
                Console.WriteLine("Initialized by thread {0}; last used by thread {1}.", _
                    large.InitializedBy, large.Data(0))
            End SyncLock
        Catch aex As ApplicationException
            Console.WriteLine("Exception: {0}", aex.Message)
        End Try
    End Sub
End Class

Friend Class LargeObject
    Private initBy As Integer = 0
    Public ReadOnly Property InitializedBy() As Integer
        Get
            Return initBy
        End Get
    End Property

    Private Shared instanceCount As Integer = 0
    Public Sub New()
        If 1 = Interlocked.Increment(instanceCount) Then
            Throw New ApplicationException("Throw only ONCE.")
        End If

        initBy = Thread.CurrentThread.ManagedThreadId
        Console.WriteLine("LargeObject was created on thread id {0}.", initBy)
    End Sub
    Public Data(99999999) As Long
End Class

' This example produces output similar to the following:
'
'LargeObject is not created until you access the Value property of the lazy
'initializer. Press Enter to create LargeObject.
'
'Exception: Throw only ONCE.
'Exception: Throw only ONCE.
'Exception: Throw only ONCE.
'
'Press Enter to end the program
'

Uwagi

Wystąpienie utworzone za pomocą tego konstruktora może być używane współbieżnie z wielu wątków.

Tryb bezpieczeństwa wątku wystąpienia Lazy<T> zainicjowanego za pomocą tego konstruktora jest LazyThreadSafetyMode.ExecutionAndPublication. Tryb bezpieczeństwa wątku opisuje zachowanie, gdy wiele wątków próbuje zainicjować wystąpienie Lazy<T>.

Wyjątki zgłaszane przez valueFactory są buforowane. Aby uzyskać więcej informacji, zobacz klasę Lazy<T> lub wyliczenie System.Threading.LazyThreadSafetyMode.

Zobacz też

• inicjowania z opóźnieniem

Lazy<T>(LazyThreadSafetyMode)

Źródło:

Lazy.cs

Inicjuje nowe wystąpienie klasy Lazy<T>, która używa konstruktora bez parametrów T i określonego trybu bezpieczeństwa wątków.

public:
 Lazy(System::Threading::LazyThreadSafetyMode mode);

public Lazy (System.Threading.LazyThreadSafetyMode mode);

new Lazy<'T> : System.Threading.LazyThreadSafetyMode -> Lazy<'T>

Public Sub New (mode As LazyThreadSafetyMode)

Parametry

mode

LazyThreadSafetyMode

Jedna z wartości wyliczenia, która określa tryb bezpieczeństwa wątku.

Wyjątki

ArgumentOutOfRangeException

mode zawiera nieprawidłową wartość.

Przykłady

W poniższym przykładzie pokazano użycie tego konstruktora do utworzenia leniwego inicjatora, który umożliwia wyścigowi wiele wątków w celu utworzenia obiektu leniwie. Wiele wątków może zakończyć się powodzeniem w tworzeniu wystąpień, ale wszystkie wątki używają wystąpienia, które zostało utworzone jako pierwsze.

Nuta

Przykład, który pokazuje, jak używać tego konstruktora w scenariuszach jednowątkowych (określając LazyThreadSafetyMode.None dla mode), zobacz konstruktor Lazy<T>(Boolean). Przykład, który pokazuje, jak używać tego konstruktora do zapewnienia blokady zamiast warunków wyścigu w scenariuszach wielowątkowym (określając LazyThreadSafetyMode.ExecutionAndPublication dla mode), zobacz konstruktor Lazy<T>().

W przykładzie zdefiniowano klasę LargeObject, która zostanie zainicjowana z opóźnieniem przez dowolny z kilku wątków. Trzy kluczowe sekcje kodu ilustrują tworzenie inicjatora, rzeczywiste inicjowanie oraz konstruktor i finalizator klasy LargeObject. Na początku metody Main przykład tworzy obiekt Lazy<T>, który wykonuje opóźnioną inicjację LargeObject:

lazyLargeObject = new Lazy<LargeObject>(LazyThreadSafetyMode.PublicationOnly);

let lazyLargeObject = Lazy<LargeObject> LazyThreadSafetyMode.PublicationOnly

lazyLargeObject = New Lazy(Of LargeObject)(LazyThreadSafetyMode.PublicationOnly)

W przykładzie są tworzone i uruchamiane trzy wątki, które blokują obiekt ManualResetEvent, dzięki czemu przykład może zwolnić wątki jednocześnie. W metodzie ThreadProc używanej przez wszystkie trzy wątki wywołanie właściwości Value tworzy wystąpienie LargeObject:

LargeObject large = lazyLargeObject.Value;

let large = lazyLargeObject.Value

Dim large As LargeObject = lazyLargeObject.Value

Ponieważ konstruktor wystąpienia Lazy<T> określonego LazyThreadSafetyMode.PublicationOnly, wszystkie trzy wątki mogą tworzyć wystąpienia LargeObject. W tym przykładzie pokazano, wyświetlając komunikaty konsoli w konstruktorze i w finalizatorze klasy LargeObject:

public LargeObject()
{
    initBy = Thread.CurrentThread.ManagedThreadId;
    Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy);
}

~LargeObject()
{
    Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy);
}

type LargeObject() =
    let initBy = Thread.CurrentThread.ManagedThreadId
    do
        printfn $"Constructor: Instance initializing on thread {initBy}"

    override _.Finalize() =
        printfn $"Finalizer: Instance was initialized on {initBy}"

Public Sub New()
    initBy = Thread.CurrentThread.ManagedThreadId
    Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy)
End Sub

Protected Overrides Sub Finalize()
    Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy)
End Sub

Jednak obiekt Lazy<T> gwarantuje, że tylko jedno wystąpienie jest używane przez wszystkie wątki. Dane wyjściowe z przykładu pokazują, że wszystkie trzy wątki używają tego samego wystąpienia, a także pokazują, że pozostałe dwa wystąpienia mogą zostać odzyskane przez odzyskiwanie pamięci.

Nuta

Dla uproszczenia w tym przykładzie użyto globalnego wystąpienia Lazy<T>, a wszystkie metody są static (Shared w Visual Basic). Nie są to wymagania dotyczące używania leniwej inicjalizacji.

using System;
using System.Threading;

class Program
{
    static Lazy<LargeObject> lazyLargeObject = null;

    static void Main()
    {
        // The lazy initializer is created here. LargeObject is not created until the
        // ThreadProc method executes.
        lazyLargeObject = new Lazy<LargeObject>(LazyThreadSafetyMode.PublicationOnly);

        // Create and start 3 threads, passing the same blocking event to all of them.
        ManualResetEvent startingGate = new ManualResetEvent(false);
        Thread[] threads = { new Thread(ThreadProc), new Thread(ThreadProc), new Thread(ThreadProc) };
        foreach (Thread t in threads)
        {
            t.Start(startingGate);
        }

        // Give all 3 threads time to start and wait, then release them all at once.
        Thread.Sleep(50);
        startingGate.Set();

        // Wait for all 3 threads to finish. (The order doesn't matter.)
        foreach (Thread t in threads)
        {
            t.Join();
        }

        Console.WriteLine(
            "\r\nThreads are complete. Running GC.Collect() to reclaim the extra instances.");

        GC.Collect();

        // Allow time for garbage collection, which happens asynchronously.
        Thread.Sleep(100);

        Console.WriteLine(
            "\r\nNote that all three threads used the instance that was not collected.");
        Console.WriteLine("Press Enter to end the program");
        Console.ReadLine();
    }

    static void ThreadProc(object state)
    {
        // Wait for the signal.
        ManualResetEvent waitForStart = (ManualResetEvent) state;
        waitForStart.WaitOne();

        LargeObject large = lazyLargeObject.Value;

        // The following line introduces an artificial delay, to exaggerate the race
        // condition.
        Thread.Sleep(5);

        // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
        //            object after creation. You must lock the object before accessing it,
        //            unless the type is thread safe. (LargeObject is not thread safe.)
        lock(large)
        {
            large.Data[0] = Thread.CurrentThread.ManagedThreadId;
            Console.WriteLine("LargeObject was initialized by thread {0}; last used by thread {1}.",
                large.InitializedBy, large.Data[0]);
        }
    }
}

class LargeObject
{
    int initBy = -1;
    public int InitializedBy { get { return initBy; } }

    public LargeObject()
    {
        initBy = Thread.CurrentThread.ManagedThreadId;
        Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy);
    }

    ~LargeObject()
    {
        Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy);
    }

    public long[] Data = new long[100000000];
}

/* This example produces output similar to the following:

Constructor: Instance initializing on thread 4
Constructor: Instance initializing on thread 3
Constructor: Instance initializing on thread 5
LargeObject was initialized by thread 4; last used by thread 4.
LargeObject was initialized by thread 4; last used by thread 5.
LargeObject was initialized by thread 4; last used by thread 3.

Threads are complete. Running GC.Collect() to reclaim the extra instances.
Finalizer: Instance was initialized on 3
Finalizer: Instance was initialized on 5

Note that all three threads used the instance that was not collected.
Press Enter to end the program

Instance finalizing; initialized on 4
 */

open System
open System.Threading

type LargeObject() =
    let initBy = Thread.CurrentThread.ManagedThreadId
    do
        printfn $"Constructor: Instance initializing on thread {initBy}"

    override _.Finalize() =
        printfn $"Finalizer: Instance was initialized on {initBy}"

    member _.InitializedBy = initBy
    member val Data = Array.zeroCreate<int64> 100000000

// The lazy initializer is created here. LargeObject is not created until the
// ThreadProc method executes.
let lazyLargeObject = Lazy<LargeObject> LazyThreadSafetyMode.PublicationOnly

let threadProc (state: obj) =
    // Wait for the signal.
    let waitForStart = state :?> ManualResetEvent
    waitForStart.WaitOne() |> ignore

    let large = lazyLargeObject.Value

    // The following line introduces an artificial delay, to exaggerate the race
    // condition.
    Thread.Sleep 5

    // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
    //            object after creation. You must lock the object before accessing it,
    //            unless the type is thread safe. (LargeObject is not thread safe.)
    lock large (fun () -> 
        large.Data[0] <- Thread.CurrentThread.ManagedThreadId
        printfn $"LargeObject was initialized by thread {large.InitializedBy} last used by thread {large.Data[0]}.")

// Create and start 3 threads, passing the same blocking event to all of them.
let startingGate = new ManualResetEvent false
let threads = 
    [| Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc) |]
for t in threads do
    t.Start startingGate

// Give all 3 threads time to start and wait, then release them all at once.
Thread.Sleep 50
startingGate.Set() |> ignore

// Wait for all 3 threads to finish. (The order doesn't matter.)
for t in threads do
    t.Join()

printfn "\nThreads are complete. Running GC.Collect() to reclaim the extra instances."

GC.Collect()

// Allow time for garbage collection, which happens asynchronously.
Thread.Sleep 100

printfn "\nNote that all three threads used the instance that was not collected."
printfn "Press Enter to end the program"
stdin.ReadLine() |> ignore


// This example produces output similar to the following:
//     Constructor: Instance initializing on thread 4
//     Constructor: Instance initializing on thread 3
//     Constructor: Instance initializing on thread 5
//     LargeObject was initialized by thread 4 last used by thread 4.
//     LargeObject was initialized by thread 4 last used by thread 5.
//     LargeObject was initialized by thread 4 last used by thread 3.
//     
//     Threads are complete. Running GC.Collect() to reclaim the extra instances.
//     Finalizer: Instance was initialized on 3
//     Finalizer: Instance was initialized on 5
//     
//     Note that all three threads used the instance that was not collected.
//     Press Enter to end the program
//     
//     Instance finalizing initialized on 4

Imports System.Threading

Friend Class Program
    Private Shared lazyLargeObject As Lazy(Of LargeObject) = Nothing

    Shared Sub Main()
        ' The lazy initializer is created here. LargeObject is not created until the 
        ' ThreadProc method executes.
        lazyLargeObject = New Lazy(Of LargeObject)(LazyThreadSafetyMode.PublicationOnly)


        ' Create and start 3 threads, passing the same blocking event to all of them.
        Dim startingGate As New ManualResetEvent(False)
        Dim threads() As Thread = { _
            New Thread(AddressOf ThreadProc), _
            New Thread(AddressOf ThreadProc), _
            New Thread(AddressOf ThreadProc) _
        }
        For Each t As Thread In threads
            t.Start(startingGate)
        Next t

        ' Give all 3 threads time to start and wait, then release them all at once.
        Thread.Sleep(50)
        startingGate.Set()

        ' Wait for all 3 threads to finish. (The order doesn't matter.)
        For Each t As Thread In threads
            t.Join()
        Next t

        Console.WriteLine(vbCrLf & _
            "Threads are complete. Running GC.Collect() to reclaim the extra instances.")

        GC.Collect()

        ' Allow time for garbage collection, which happens asynchronously.
        Thread.Sleep(100)

        Console.WriteLine(vbCrLf & _
            "Note that all three threads used the instance that was not collected.")
        Console.WriteLine("Press Enter to end the program")
        Console.ReadLine()

    End Sub


    Private Shared Sub ThreadProc(ByVal state As Object)
        ' Wait for the signal.
        Dim waitForStart As ManualResetEvent = CType(state, ManualResetEvent)
        waitForStart.WaitOne()

        Dim large As LargeObject = lazyLargeObject.Value

        ' The following line introduces an artificial delay to exaggerate the race condition.
        Thread.Sleep(5)

        ' IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the  
        '            object after creation. You must lock the object before accessing it,
        '            unless the type is thread safe. (LargeObject is not thread safe.)
        SyncLock large
            large.Data(0) = Thread.CurrentThread.ManagedThreadId
            Console.WriteLine( _
                "LargeObject was initialized by thread {0}; last used by thread {1}.", _
                large.InitializedBy, large.Data(0))
        End SyncLock
    End Sub
End Class

Friend Class LargeObject
    Private initBy As Integer = -1
    Public ReadOnly Property InitializedBy() As Integer
        Get
            Return initBy
        End Get
    End Property

    Public Sub New()
        initBy = Thread.CurrentThread.ManagedThreadId
        Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy)
    End Sub

    Protected Overrides Sub Finalize()
        Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy)
    End Sub

    Public Data(100000000) As Long
End Class

' This example produces output similar to the following:
'
'Constructor: Instance initializing on thread 3
'Constructor: Instance initializing on thread 5
'Constructor: Instance initializing on thread 4
'LargeObject was initialized by thread 3; last used by thread 4.
'LargeObject was initialized by thread 3; last used by thread 3.
'LargeObject was initialized by thread 3; last used by thread 5.
'
'Threads are complete. Running GC.Collect() to reclaim the extra instances.
'Finalizer: Instance was initialized on 5
'Finalizer: Instance was initialized on 4
'
'Note that all three threads used the instance that was not collected.
'Press Enter to end the program
'
'Finalizer: Instance was initialized on 3
'

Uwagi

Tryb bezpieczeństwa wątku wystąpienia Lazy<T> opisuje zachowanie, gdy wiele wątków próbuje zainicjować wystąpienie Lazy<T>.

Wystąpienie Lazy<T> utworzone za pomocą tego konstruktora nie buforuje wyjątków. Aby uzyskać więcej informacji, zobacz klasę Lazy<T> lub wyliczenie System.Threading.LazyThreadSafetyMode.

Zobacz też

• LazyThreadSafetyMode
• inicjowania z opóźnieniem

Lazy<T>(T)

Źródło:

Lazy.cs

Inicjuje nowe wystąpienie klasy Lazy<T>, która używa wstępnie zdefiniowanej wartości.

public:
 Lazy(T value);

public Lazy (T value);

new Lazy<'T> : 'T -> Lazy<'T>

Public Sub New (value As T)

Parametry

value

T

Wstępnie zainicjowana wartość do użycia.

Uwagi

Wystąpienie utworzone za pomocą tego konstruktora może być używane przez wiele wątków jednocześnie.

Lazy<T>(Func<T>, Boolean)

Źródło:

Lazy.cs

Inicjuje nowe wystąpienie klasy Lazy<T>. Gdy wystąpi opóźnienie inicjowania, używana jest określona funkcja inicjowania i tryb inicjowania.

public:
 Lazy(Func<T> ^ valueFactory, bool isThreadSafe);

public Lazy (Func<T> valueFactory, bool isThreadSafe);

new Lazy<'T> : Func<'T> * bool -> Lazy<'T>

Public Sub New (valueFactory As Func(Of T), isThreadSafe As Boolean)

Parametry

valueFactory

Func<T>

Delegat, który jest wywoływany w celu utworzenia leniwie zainicjowanej wartości, gdy jest potrzebny.

isThreadSafe

Boolean

true, aby to wystąpienie było używane współbieżnie przez wiele wątków; false, aby to wystąpienie było używane tylko przez jeden wątek naraz.

Wyjątki

ArgumentNullException

valueFactory jest null.

Przykłady

W poniższym przykładzie pokazano użycie tego konstruktora w celu zapewnienia opóźnionego inicjowania z buforowaniem wyjątków w scenariuszu z jednym wątkiem. Demonstruje również użycie konstruktora Lazy<T> (określając LazyThreadSafetyMode.None dla mode). Aby przełączyć się do tego konstruktora, wystarczy zmienić, który konstruktor jest skomentowany.

Nuta

Aby uzyskać kod, który pokazuje, jak używać tego konstruktora w scenariuszach wielowątkowym (określając true dla isThreadSafe), zobacz przykład konstruktora Lazy<T>(Func<T>).

W przykładzie zdefiniowano klasę LargeObject, która zostanie zainicjowana z opóźnieniem przez jeden z kilku wątków. Trzy kluczowe sekcje kodu ilustrują tworzenie inicjatora, rzeczywiste inicjowanie i konstruktor klasy LargeObject, która demonstruje buforowanie wyjątków. Na początku metody Main przykład tworzy bezpieczny wątkowo inicjator leniwy dla LargeObject:

lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, false);

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, LazyThreadSafetyMode.None);

let lazyLargeObject = Lazy<LargeObject>(initLargeObject, false)

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//     let lazyLargeObject = Lazy<LargeObject>(initLargeObject, LazyThreadSafetyMode.None)

lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, False)

' The following lines show how to use other constructors to achieve exactly the
' same result as the previous line: 
'lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, LazyThreadSafetyMode.None)

W wywołaniu konstruktora parametr isThreadSafe jest false, więc Lazy<T> nie jest bezpieczny wątkiem. Ponieważ nie jest bezpieczny wątek, przykład wywołuje właściwość Value trzy razy w tym samym wątku:

for (int i = 0; i < 3; i++)
{
    try
    {
        LargeObject large = lazyLargeObject.Value;
        large.Data[11] = 89;
    }
    catch (ApplicationException aex)
    {
        Console.WriteLine("Exception: {0}", aex.Message);
    }
}

for _ = 0 to 2 do
    try
        let large = lazyLargeObject.Value
        large.Data[11] <- 89
    with :? ApplicationException as aex ->
        printfn $"Exception: {aex.Message}"

For i As Integer = 0 To 2
    Try
        Dim large As LargeObject = lazyLargeObject.Value
        large.Data(11) = 89
    Catch aex As ApplicationException
        Console.WriteLine("Exception: {0}", aex.Message)
    End Try
Next i

W konstruktorze klasy LargeObject trzecia sekcja klucza kodu zgłasza wyjątek przy pierwszym utworzeniu wystąpienia LargeObject, ale następnie umożliwia utworzenie wystąpienia:

static bool pleaseThrow = true;
public LargeObject()
{
    if (pleaseThrow)
    {
        pleaseThrow = false;
        throw new ApplicationException("Throw only ONCE.");
    }

    Console.WriteLine("LargeObject was created on thread id {0}.",
        Thread.CurrentThread.ManagedThreadId);
}

type LargeObject() =
    static let mutable pleaseThrow = true
    do
        if pleaseThrow then
            pleaseThrow <- false
            raise (ApplicationException "Throw only ONCE.")
        printfn $"LargeObject was created on thread id {Thread.CurrentThread.ManagedThreadId}."

Private Shared pleaseThrow As Boolean = True
Public Sub New()
    If pleaseThrow Then
        pleaseThrow = False
        Throw New ApplicationException("Throw only ONCE.")
    End If

    Console.WriteLine("LargeObject was created on thread id {0}.", _
        Thread.CurrentThread.ManagedThreadId)
End Sub

Po uruchomieniu przykładu pierwsza próba utworzenia wystąpienia LargeObject zakończy się niepowodzeniem, a wyjątek zostanie przechwycony. Można oczekiwać, że następna próba powiedzie się, ale obiekt Lazy<T> buforował wyjątek. W związku z tym wszystkie trzy próby zgłaszają wyjątek.

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Dla uproszczenia w tym przykładzie użyto globalnego wystąpienia Lazy<T>, a wszystkie metody są static (Shared w Visual Basic). Nie są to wymagania dotyczące używania leniwej inicjalizacji.

using System;
using System.Threading;

class Program
{
    static Lazy<LargeObject> lazyLargeObject = null;

    static LargeObject InitLargeObject()
    {
        return new LargeObject();
    }

    static void Main()
    {
        // The lazy initializer is created here. LargeObject is not created until the
        // ThreadProc method executes.
        lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, false);

        // The following lines show how to use other constructors to achieve exactly the
        // same result as the previous line:
        //lazyLargeObject = new Lazy<LargeObject>(InitLargeObject, LazyThreadSafetyMode.None);

        Console.WriteLine(
            "\r\nLargeObject is not created until you access the Value property of the lazy" +
            "\r\ninitializer. Press Enter to create LargeObject (three tries).");
        Console.ReadLine();

        for (int i = 0; i < 3; i++)
        {
            try
            {
                LargeObject large = lazyLargeObject.Value;
                large.Data[11] = 89;
            }
            catch (ApplicationException aex)
            {
                Console.WriteLine("Exception: {0}", aex.Message);
            }
        }

        Console.WriteLine("\r\nPress Enter to end the program");
        Console.ReadLine();
    }
}

class LargeObject
{
    static bool pleaseThrow = true;
    public LargeObject()
    {
        if (pleaseThrow)
        {
            pleaseThrow = false;
            throw new ApplicationException("Throw only ONCE.");
        }

        Console.WriteLine("LargeObject was created on thread id {0}.",
            Thread.CurrentThread.ManagedThreadId);
    }
    public long[] Data = new long[100000000];
}

/* This example produces output similar to the following:

LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject (three tries).

Exception: Throw only ONCE.
Exception: Throw only ONCE.
Exception: Throw only ONCE.

Press Enter to end the program
 */

open System
open System.Threading

type LargeObject() =
    static let mutable pleaseThrow = true
    do
        if pleaseThrow then
            pleaseThrow <- false
            raise (ApplicationException "Throw only ONCE.")
        printfn $"LargeObject was created on thread id {Thread.CurrentThread.ManagedThreadId}."
    member val Data = Array.zeroCreate<int64> 100000000

let initLargeObject () =
    LargeObject()

// The lazy initializer is created here. LargeObject is not created until the
// ThreadProc method executes.
let lazyLargeObject = Lazy<LargeObject>(initLargeObject, false)

// The following lines show how to use other constructors to achieve exactly the
// same result as the previous line:
//     let lazyLargeObject = Lazy<LargeObject>(initLargeObject, LazyThreadSafetyMode.None)

printfn """
LargeObject is not created until you access the Value property of the lazy
initializer. Press Enter to create LargeObject (three tries)."""
stdin.ReadLine() |> ignore

for _ = 0 to 2 do
    try
        let large = lazyLargeObject.Value
        large.Data[11] <- 89
    with :? ApplicationException as aex ->
        printfn $"Exception: {aex.Message}"

printfn "\nPress Enter to end the program"
stdin.ReadLine() |> ignore

// This example produces output similar to the following:
//     LargeObject is not created until you access the Value property of the lazy
//     initializer. Press Enter to create LargeObject (three tries).
//     
//     Exception: Throw only ONCE.
//     Exception: Throw only ONCE.
//     Exception: Throw only ONCE.
//     
//     Press Enter to end the program

Imports System.Threading

Friend Class Program
    Private Shared lazyLargeObject As Lazy(Of LargeObject) = Nothing

    Private Shared Function InitLargeObject() As LargeObject
        Return New LargeObject()
    End Function


    Shared Sub Main()
        ' The lazy initializer is created here. LargeObject is not created until the 
        ' ThreadProc method executes.
        lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, False)

        ' The following lines show how to use other constructors to achieve exactly the
        ' same result as the previous line: 
        'lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, LazyThreadSafetyMode.None)


        Console.WriteLine(vbCrLf _
            & "LargeObject is not created until you access the Value property of the lazy" _
            & vbCrLf & "initializer. Press Enter to create LargeObject (three tries).")
        Console.ReadLine()

        For i As Integer = 0 To 2
            Try
                Dim large As LargeObject = lazyLargeObject.Value
                large.Data(11) = 89
            Catch aex As ApplicationException
                Console.WriteLine("Exception: {0}", aex.Message)
            End Try
        Next i

        Console.WriteLine(vbCrLf & "Press Enter to end the program")
        Console.ReadLine()
    End Sub
End Class

Friend Class LargeObject
    Private Shared pleaseThrow As Boolean = True
    Public Sub New()
        If pleaseThrow Then
            pleaseThrow = False
            Throw New ApplicationException("Throw only ONCE.")
        End If

        Console.WriteLine("LargeObject was created on thread id {0}.", _
            Thread.CurrentThread.ManagedThreadId)
    End Sub
    Public Data(100000000) As Long
End Class

' This example produces output similar to the following:
'
'LargeObject is not created until you access the Value property of the lazy
'initializer. Press Enter to create LargeObject (three tries).
'
'Exception: Throw only ONCE.
'Exception: Throw only ONCE.
'Exception: Throw only ONCE.
'
'Press Enter to end the program
'

Uwagi

Tryb bezpieczeństwa wątku wystąpienia Lazy<T> zainicjowanego za pomocą tego konstruktora jest LazyThreadSafetyMode.ExecutionAndPublication, jeśli isThreadSafe jest true; w przeciwnym razie tryb jest LazyThreadSafetyMode.None. Tryb bezpieczeństwa wątku opisuje zachowanie, gdy wiele wątków próbuje zainicjować wystąpienie Lazy<T>.

Aby określić tryb LazyThreadSafetyMode.PublicationOnly, użyj konstruktora Lazy<T>(Func<T>, LazyThreadSafetyMode) lub Lazy<T>(LazyThreadSafetyMode).

Wyjątki zgłaszane przez valueFactory są buforowane. Aby uzyskać więcej informacji, zobacz klasę Lazy<T> lub wyliczenie System.Threading.LazyThreadSafetyMode.

Zobacz też

• inicjowania z opóźnieniem

Lazy<T>(Func<T>, LazyThreadSafetyMode)

Źródło:

Lazy.cs

Inicjuje nowe wystąpienie klasy Lazy<T>, która używa określonej funkcji inicjowania i trybu bezpieczeństwa wątków.

public:
 Lazy(Func<T> ^ valueFactory, System::Threading::LazyThreadSafetyMode mode);

public Lazy (Func<T> valueFactory, System.Threading.LazyThreadSafetyMode mode);

new Lazy<'T> : Func<'T> * System.Threading.LazyThreadSafetyMode -> Lazy<'T>

Public Sub New (valueFactory As Func(Of T), mode As LazyThreadSafetyMode)

Parametry

valueFactory

Func<T>

Delegat, który jest wywoływany w celu utworzenia leniwie zainicjowanej wartości, gdy jest potrzebny.

mode

LazyThreadSafetyMode

Jedna z wartości wyliczenia, która określa tryb bezpieczeństwa wątku.

Wyjątki

ArgumentOutOfRangeException

mode zawiera nieprawidłową wartość.

ArgumentNullException

valueFactory jest null.

Przykłady

W poniższym przykładzie pokazano użycie tego konstruktora do utworzenia leniwego inicjatora, który umożliwia wyścigowi wiele wątków w celu utworzenia obiektu leniwie. Wiele wątków może zakończyć się powodzeniem w tworzeniu wystąpień, ale wszystkie wątki używają wystąpienia, które zostało utworzone jako pierwsze. Ponadto w przykładzie pokazano, że wyjątki nigdy nie są buforowane podczas określania LazyThreadSafetyMode.PublicationOnly, nawet jeśli inicjowanie jest wykonywane przez funkcję zamiast przez konstruktor bez parametrów typu utworzonego z opóźnieniem.

Nuta

Przykład, który pokazuje, jak używać tego konstruktora w scenariuszach jednowątkowych (określając LazyThreadSafetyMode.None dla mode), zobacz konstruktor Lazy<T>(Boolean). Przykład, który pokazuje, jak używać tego konstruktora do zapewnienia blokady zamiast warunków wyścigu w scenariuszach wielowątkowym (określając LazyThreadSafetyMode.ExecutionAndPublication dla mode), zobacz konstruktor Lazy<T>().

W przykładzie zdefiniowano klasę LargeObject, która zostanie zainicjowana z opóźnieniem przez dowolny z kilku wątków. Cztery kluczowe sekcje kodu ilustrują tworzenie inicjatora, rzeczywiste inicjowanie, funkcję inicjowania oraz konstruktor i finalizator klasy LargeObject. Na początku metody Main przykład tworzy obiekt Lazy<T>, który wykonuje opóźnioną inicjację LargeObject:

lazyLargeObject = new Lazy<LargeObject>(InitLargeObject,
                             LazyThreadSafetyMode.PublicationOnly);

let lazyLargeObject = Lazy<LargeObject>(initLargeObject, LazyThreadSafetyMode.PublicationOnly)

lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, _
     LazyThreadSafetyMode.PublicationOnly)

Inicjator leniwy używa funkcji do wykonania inicjowania. W takim przypadku wymagana jest funkcja, ponieważ nie ma konstruktora bez parametrów dla klasy LargeObject.

W przykładzie są tworzone i uruchamiane trzy wątki, które blokują obiekt ManualResetEvent, dzięki czemu przykład może zwolnić wątki jednocześnie. W metodzie ThreadProc używanej przez wszystkie trzy wątki wywołanie właściwości Value tworzy wystąpienie LargeObject:

LargeObject large = null;
try
{
    large = lazyLargeObject.Value;

    // The following line introduces an artificial delay to exaggerate the race condition.
    Thread.Sleep(5);

    // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
    //            object after creation. You must lock the object before accessing it,
    //            unless the type is thread safe. (LargeObject is not thread safe.)
    lock(large)
    {
        large.Data[0] = Thread.CurrentThread.ManagedThreadId;
        Console.WriteLine("LargeObject was initialized by thread {0}; last used by thread {1}.",
            large.InitializedBy, large.Data[0]);
    }
}
catch (ApplicationException ex)
{
    Console.WriteLine("ApplicationException: {0}", ex.Message);
}

try
    let large = lazyLargeObject.Value

    // The following line introduces an artificial delay to exaggerate the race condition.
    Thread.Sleep 5

    // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
    //            object after creation. You must lock the object before accessing it,
    //            unless the type is thread safe. (LargeObject is not thread safe.)
    lock large (fun () -> 
        large.Data[0] <- Thread.CurrentThread.ManagedThreadId
        printfn $"LargeObject was initialized by thread {large.InitializedBy} last used by thread {large.Data[0]}.")
with :? ApplicationException as ex ->
    printfn $"ApplicationException: {ex.Message}"

Dim large As LargeObject = Nothing
Try
    large = lazyLargeObject.Value

    ' The following line introduces an artificial delay to exaggerate the race condition.
    Thread.Sleep(5)

    ' IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the  
    '            object after creation. You must lock the object before accessing it,
    '            unless the type is thread safe. (LargeObject is not thread safe.)
    SyncLock large
        large.Data(0) = Thread.CurrentThread.ManagedThreadId
        Console.WriteLine( _
            "LargeObject was initialized by thread {0}; last used by thread {1}.", _
            large.InitializedBy, large.Data(0))
    End SyncLock
Catch ex As ApplicationException
    Console.WriteLine("ApplicationException: {0}", ex.Message)
End Try

W trzeciej sekcji klucza kodu wywoływana jest funkcja inicjowania z opóźnieniem w celu utworzenia wystąpienia LargeObject. Funkcja zgłasza wyjątek przy pierwszym wywołaniu:

static int instanceCount = 0;
static LargeObject InitLargeObject()
{
    if (1 == Interlocked.Increment(ref instanceCount))
    {
        throw new ApplicationException(
            String.Format("Lazy initialization function failed on thread {0}.",
            Thread.CurrentThread.ManagedThreadId));
    }
    return new LargeObject(Thread.CurrentThread.ManagedThreadId);
}

let mutable instanceCount = 0
let initLargeObject () =
    if 1 = Interlocked.Increment &instanceCount then
        raise (ApplicationException $"Lazy initialization function failed on thread {Thread.CurrentThread.ManagedThreadId}.")
    LargeObject Thread.CurrentThread.ManagedThreadId

Private Shared instanceCount As Integer = 0
Private Shared Function InitLargeObject() As LargeObject
    If 1 = Interlocked.Increment(instanceCount) Then
        Throw New ApplicationException( _
            "Lazy initialization function failed on thread " & _
            Thread.CurrentThread.ManagedThreadId & ".")
    End If
    Return New LargeObject(Thread.CurrentThread.ManagedThreadId)
End Function

W przypadku dowolnego innego ustawienia LazyThreadSafetyMode buforowany będzie nieobsługiwany wyjątek w funkcji inicjowania. Jednak LazyThreadSafetyMode.PublicationOnly pomija buforowanie wyjątków. Dane wyjściowe z przykładu pokazują, że kolejna próba zainicjowania obiektu zakończy się powodzeniem.

Nuta

Komunikat o wyjątku zwykle pojawia się po komunikatach wskazujących, że inne wątki pomyślnie zainicjowały obiekt. Wynika to z opóźnienia wprowadzonego przez zgłaszanie i przechwytywanie wyjątku.

Ponieważ konstruktor wystąpienia Lazy<T> określonego LazyThreadSafetyMode.PublicationOnly, wszystkie trzy wątki mogą tworzyć wystąpienia LargeObject. W tym przykładzie pokazano, wyświetlając komunikaty konsoli w konstruktorze i w finalizatorze klasy LargeObject:

public LargeObject(int initializedBy)
{
    initBy = initializedBy;
    Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy);
}

~LargeObject()
{
    Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy);
}

type LargeObject(initBy) =
    do
        printfn $"Constructor: Instance initializing on thread {initBy}"

    override _.Finalize() =
        printfn $"Finalizer: Instance was initialized on {initBy}"

Public Sub New(ByVal initializedBy As Integer)
    initBy = initializedBy
    Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy)
End Sub

Protected Overrides Sub Finalize()
    Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy)
End Sub

Obiekt Lazy<T> zapewnia, że tylko jedno wystąpienie jest używane przez wszystkie wątki (z wyjątkiem wątku, w którym funkcja inicjowania zgłasza wyjątek). Dane wyjściowe z przykładu pokazują to.

Nuta

Dla uproszczenia w tym przykładzie użyto globalnego wystąpienia Lazy<T>, a wszystkie metody są static (Shared w Visual Basic). Nie są to wymagania dotyczące używania leniwej inicjalizacji.

using System;
using System.Threading;

class Program
{
    static Lazy<LargeObject> lazyLargeObject = null;

    // Factory function for lazy initialization.
    static int instanceCount = 0;
    static LargeObject InitLargeObject()
    {
        if (1 == Interlocked.Increment(ref instanceCount))
        {
            throw new ApplicationException(
                String.Format("Lazy initialization function failed on thread {0}.",
                Thread.CurrentThread.ManagedThreadId));
        }
        return new LargeObject(Thread.CurrentThread.ManagedThreadId);
    }

    static void Main()
    {
        // The lazy initializer is created here. LargeObject is not created until the
        // ThreadProc method executes.
        lazyLargeObject = new Lazy<LargeObject>(InitLargeObject,
                                     LazyThreadSafetyMode.PublicationOnly);

        // Create and start 3 threads, passing the same blocking event to all of them.
        ManualResetEvent startingGate = new ManualResetEvent(false);
        Thread[] threads = { new Thread(ThreadProc), new Thread(ThreadProc), new Thread(ThreadProc) };
        foreach (Thread t in threads)
        {
            t.Start(startingGate);
        }

        // Give all 3 threads time to start and wait, then release them all at once.
        Thread.Sleep(50);
        startingGate.Set();

        // Wait for all 3 threads to finish. (The order doesn't matter.)
        foreach (Thread t in threads)
        {
            t.Join();
        }

        Console.WriteLine(
            "\r\nThreads are complete. Running GC.Collect() to reclaim extra instances.");

        GC.Collect();

        // Allow time for garbage collection, which happens asynchronously.
        Thread.Sleep(100);

        Console.WriteLine("\r\nNote that only one instance of LargeObject was used.");
        Console.WriteLine("Press Enter to end the program");
        Console.ReadLine();
    }

    static void ThreadProc(object state)
    {
        // Wait for the signal.
        ManualResetEvent waitForStart = (ManualResetEvent) state;
        waitForStart.WaitOne();

        LargeObject large = null;
        try
        {
            large = lazyLargeObject.Value;

            // The following line introduces an artificial delay to exaggerate the race condition.
            Thread.Sleep(5);

            // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
            //            object after creation. You must lock the object before accessing it,
            //            unless the type is thread safe. (LargeObject is not thread safe.)
            lock(large)
            {
                large.Data[0] = Thread.CurrentThread.ManagedThreadId;
                Console.WriteLine("LargeObject was initialized by thread {0}; last used by thread {1}.",
                    large.InitializedBy, large.Data[0]);
            }
        }
        catch (ApplicationException ex)
        {
            Console.WriteLine("ApplicationException: {0}", ex.Message);
        }
    }
}

class LargeObject
{
    int initBy = -1;
    public int InitializedBy { get { return initBy; } }

    public LargeObject(int initializedBy)
    {
        initBy = initializedBy;
        Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy);
    }

    ~LargeObject()
    {
        Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy);
    }

    public long[] Data = new long[100000000];
}

/* This example produces output similar to the following:

Constructor: Instance initializing on thread 5
Constructor: Instance initializing on thread 4
ApplicationException: Lazy initialization function failed on thread 3.
LargeObject was initialized by thread 5; last used by thread 5.
LargeObject was initialized by thread 5; last used by thread 4.

Threads are complete. Running GC.Collect() to reclaim extra instances.
Finalizer: Instance was initialized on 4

Note that only one instance of LargeObject was used.
Press Enter to end the program

Finalizer: Instance was initialized on 5
 */

open System
open System.Threading

type LargeObject(initBy) =
    do
        printfn $"Constructor: Instance initializing on thread {initBy}"

    override _.Finalize() =
        printfn $"Finalizer: Instance was initialized on {initBy}"
    member _.InitializedBy = initBy
    member val Data = Array.zeroCreate<int64> 100000000 with get

// Factory function for lazy initialization.
let mutable instanceCount = 0
let initLargeObject () =
    if 1 = Interlocked.Increment &instanceCount then
        raise (ApplicationException $"Lazy initialization function failed on thread {Thread.CurrentThread.ManagedThreadId}.")
    LargeObject Thread.CurrentThread.ManagedThreadId

// The lazy initializer is created here. LargeObject is not created until the
// ThreadProc method executes.
let lazyLargeObject = Lazy<LargeObject>(initLargeObject, LazyThreadSafetyMode.PublicationOnly)

let threadProc (state: obj) =
    // Wait for the signal.
    let waitForStart = state :?> ManualResetEvent
    waitForStart.WaitOne() |> ignore

    try
        let large = lazyLargeObject.Value

        // The following line introduces an artificial delay to exaggerate the race condition.
        Thread.Sleep 5

        // IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the
        //            object after creation. You must lock the object before accessing it,
        //            unless the type is thread safe. (LargeObject is not thread safe.)
        lock large (fun () -> 
            large.Data[0] <- Thread.CurrentThread.ManagedThreadId
            printfn $"LargeObject was initialized by thread {large.InitializedBy} last used by thread {large.Data[0]}.")
    with :? ApplicationException as ex ->
        printfn $"ApplicationException: {ex.Message}"

// Create and start 3 threads, passing the same blocking event to all of them.
let startingGate = new ManualResetEvent false
let threads = 
    [| Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc); Thread(ParameterizedThreadStart threadProc) |]
for t in threads do
    t.Start startingGate

// Give all 3 threads time to start and wait, then release them all at once.
Thread.Sleep 50
startingGate.Set() |> ignore

// Wait for all 3 threads to finish. (The order doesn't matter.)
for t in threads do
    t.Join()

printfn "\nThreads are complete. Running GC.Collect() to reclaim extra instances."

GC.Collect()

// Allow time for garbage collection, which happens asynchronously.
Thread.Sleep 100

printfn "\nNote that only one instance of LargeObject was used."
printfn "Press Enter to end the program"
stdin.ReadLine() |> ignore

// This example produces output similar to the following:
//     Constructor: Instance initializing on thread 5
//     Constructor: Instance initializing on thread 4
//     ApplicationException: Lazy initialization function failed on thread 3.
//     LargeObject was initialized by thread 5 last used by thread 5.
//     LargeObject was initialized by thread 5 last used by thread 4.
//     
//     Threads are complete. Running GC.Collect() to reclaim extra instances.
//     Finalizer: Instance was initialized on 4
//     
//     Note that only one instance of LargeObject was used.
//     Press Enter to end the program
//     
//     Finalizer: Instance was initialized on 5

Imports System.Threading

Friend Class Program
    Private Shared lazyLargeObject As Lazy(Of LargeObject) = Nothing

    ' Factory function for lazy initialization.
    Private Shared instanceCount As Integer = 0
    Private Shared Function InitLargeObject() As LargeObject
        If 1 = Interlocked.Increment(instanceCount) Then
            Throw New ApplicationException( _
                "Lazy initialization function failed on thread " & _
                Thread.CurrentThread.ManagedThreadId & ".")
        End If
        Return New LargeObject(Thread.CurrentThread.ManagedThreadId)
    End Function

    Shared Sub Main()
        ' The lazy initializer is created here. LargeObject is not created until the 
        ' ThreadProc method executes.
        lazyLargeObject = New Lazy(Of LargeObject)(AddressOf InitLargeObject, _
             LazyThreadSafetyMode.PublicationOnly)


        ' Create and start 3 threads, passing the same blocking event to all of them.
        Dim startingGate As New ManualResetEvent(False)
        Dim threads() As Thread = { _
            New Thread(AddressOf ThreadProc), _
            New Thread(AddressOf ThreadProc), _
            New Thread(AddressOf ThreadProc) _
        }
        For Each t As Thread In threads
            t.Start(startingGate)
        Next t

        ' Give all 3 threads time to start and wait, then release them all at once.
        Thread.Sleep(50)
        startingGate.Set()

        ' Wait for all 3 threads to finish. (The order doesn't matter.)
        For Each t As Thread In threads
            t.Join()
        Next t

        Console.WriteLine(vbCrLf & _
            "Threads are complete. Running GC.Collect() to reclaim extra instances.")

        GC.Collect()

        ' Allow time for garbage collection, which happens asynchronously.
        Thread.Sleep(100)

        Console.WriteLine(vbCrLf & "Note that only one instance of LargeObject was used.")
        Console.WriteLine("Press Enter to end the program")
        Console.ReadLine()
    End Sub


    Private Shared Sub ThreadProc(ByVal state As Object)
        ' Wait for the signal.
        Dim waitForStart As ManualResetEvent = CType(state, ManualResetEvent)
        waitForStart.WaitOne()

        Dim large As LargeObject = Nothing
        Try
            large = lazyLargeObject.Value

            ' The following line introduces an artificial delay to exaggerate the race condition.
            Thread.Sleep(5)

            ' IMPORTANT: Lazy initialization is thread-safe, but it doesn't protect the  
            '            object after creation. You must lock the object before accessing it,
            '            unless the type is thread safe. (LargeObject is not thread safe.)
            SyncLock large
                large.Data(0) = Thread.CurrentThread.ManagedThreadId
                Console.WriteLine( _
                    "LargeObject was initialized by thread {0}; last used by thread {1}.", _
                    large.InitializedBy, large.Data(0))
            End SyncLock
        Catch ex As ApplicationException
            Console.WriteLine("ApplicationException: {0}", ex.Message)
        End Try
    End Sub
End Class

Friend Class LargeObject
    Private initBy As Integer = -1
    Public ReadOnly Property InitializedBy() As Integer
        Get
            Return initBy
        End Get
    End Property

    Public Sub New(ByVal initializedBy As Integer)
        initBy = initializedBy
        Console.WriteLine("Constructor: Instance initializing on thread {0}", initBy)
    End Sub

    Protected Overrides Sub Finalize()
        Console.WriteLine("Finalizer: Instance was initialized on {0}", initBy)
    End Sub

    Public Data(99999999) As Long
End Class

' This example produces output similar to the following:
'
'Constructor: Instance initializing on thread 4
'ApplicationException: Lazy initialization function failed on thread 3.
'Constructor: Instance initializing on thread 5
'LargeObject was initialized by thread 4; last used by thread 4.
'LargeObject was initialized by thread 4; last used by thread 5.
'
'Threads are complete. Running GC.Collect() to reclaim extra instances.
'Finalizer: Instance was initialized on 5
'
'Note that only one instance of LargeObject was used.
'Press Enter to end the program
'
'Finalizer: Instance was initialized on 4
'

Uwagi

Tryb bezpieczeństwa wątku wystąpienia Lazy<T> opisuje zachowanie, gdy wiele wątków próbuje zainicjować wystąpienie Lazy<T>.

Wyjątki zgłaszane przez valueFactory są buforowane, chyba że mode jest LazyThreadSafetyMode.PublicationOnly. Aby uzyskać więcej informacji, zobacz klasę Lazy<T> lub wyliczenie System.Threading.LazyThreadSafetyMode.

Zobacz też

• inicjowania z opóźnieniem