방법: ConcurrentDictionary에서 항목 추가 및 제거
이 예제에서는 System.Collections.Concurrent.ConcurrentDictionary<TKey, TValue>의 항목을 추가, 검색, 업데이트 및 제거하는 방법을 보여 줍니다. 이 컬렉션 클래스는 스레드로부터 안전하게 구현되어 있습니다. 여러 스레드에서 동시에 컬렉션에 액세스할 가능성이 있는 경우에는 항상 이 클래스를 사용하는 것이 좋습니다.
ConcurrentDictionary<TKey, TValue>에서는 데이터를 추가 또는 제거하려고 하기 전에 키의 존재 여부를 먼저 확인하는 코드가 필요 없도록 하는 편리한 메서드를 여러 가지 제공합니다. 다음 표에서는 이와 같은 편리한 메서드를 나열하고 해당 메서드가 사용되는 경우에 대해 설명합니다.
메서드 |
용도 |
|---|---|
지정된 키의 새 값을 추가하고 키가 이미 있으면 키 값을 바꾸려는 경우 |
|
지정된 키의 기존 값을 검색하고 키가 아직 없으면 키/값 쌍을 지정하려는 경우 |
|
키/값 쌍을 추가하고, 가져오고, 업데이트하거나 제거하려는 경우. 이러한 시도가 어떤 이유로 인해 실패하거나 키가 이미 있으면 다른 작업을 대신 수행하려는 경우 |
예제
다음 예제에서는 Task 인스턴스 두 개를 사용하여 ConcurrentDictionary<TKey, TValue>에 일부 요소를 동시에 추가한 다음 모든 내용을 출력하여 요소가 성공적으로 추가되었음을 보여 줍니다. 또한 이 예제에서는 AddOrUpdate, TryGetValue, GetOrAdd 및 TryRemove 메서드를 사용하여 컬렉션의 항목을 추가, 업데이트, 검색 및 제거하는 방법을 보여 줍니다.
Imports System
Imports System.Collections.Concurrent
Imports System.Collections.Generic
Imports System.Linq
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace DictionaryHowToVB
' The type of the value to store in the dictionary
Class CityInfo
Private _name As String
Property Name As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Private _lastQueryDate As DateTime
Property LastQueryDate As DateTime
Get
Return _lastQueryDate
End Get
Set(ByVal value As DateTime)
_lastQueryDate = value
End Set
End Property
Private _longitude As Decimal
Property Longitude As Decimal
Get
Return _longitude
End Get
Set(ByVal value As Decimal)
_longitude = value
End Set
End Property
Private _latitude As Decimal
Property Latitude As Decimal
Get
Return _latitude
End Get
Set(ByVal value As Decimal)
_latitude = value
End Set
End Property
Private _highTemps() As Integer
Property RecentHighTemperatures As Integer()
Get
Return _highTemps
End Get
Set(ByVal value As Integer())
_highTemps = value
End Set
End Property
Public Sub New()
End Sub
Public Sub New(ByVal key As String)
_name = key
' MaxValue means "not initialized"
_longitude = Decimal.MaxValue
_latitude = Decimal.MaxValue
_lastQueryDate = DateTime.Now
_highTemps = {0}
End Sub
Public Sub New(ByVal name As String, ByVal longitude As Decimal,
ByVal latitude As Decimal, ByVal temps As Integer())
_name = name
_longitude = longitude
_latitude = latitude
_highTemps = temps
End Sub
End Class
Class Program
' Create a new concurrent dictionary with the specified concurrency level and capacity.
Shared cities As New ConcurrentDictionary(Of String, CityInfo)(System.Environment.ProcessorCount, 10)
Shared Sub Main()
Dim data As CityInfo() =
{New CityInfo With {.Name = "Boston", .Latitude = 42.358769, .Longitude = -71.057806, .RecentHighTemperatures = {56, 51, 52, 58, 65, 56, 53}},
New CityInfo With {.Name = "Miami", .Latitude = 25.780833, .Longitude = -80.195556, .RecentHighTemperatures = {86, 87, 88, 87, 85, 85, 86}},
New CityInfo With {.Name = "Los Angeles", .Latitude = 34.05, .Longitude = -118.25, .RecentHighTemperatures = {67, 68, 69, 73, 79, 78, 78}},
New CityInfo With {.Name = "Seattle", .Latitude = 47.609722, .Longitude = -122.333056, .RecentHighTemperatures = {49, 50, 53, 47, 52, 52, 51}},
New CityInfo With {.Name = "Toronto", .Latitude = 43.716589, .Longitude = -79.340686, .RecentHighTemperatures = {53, 57, 51, 52, 56, 55, 50}},
New CityInfo With {.Name = "Mexico City", .Latitude = 19.432736, .Longitude = -99.133253, .RecentHighTemperatures = {72, 68, 73, 77, 76, 74, 73}},
New CityInfo With {.Name = "Rio de Janiero", .Latitude = -22.908333, .Longitude = -43.196389, .RecentHighTemperatures = {72, 68, 73, 82, 84, 78, 84}},
New CityInfo With {.Name = "Quito", .Latitude = -0.25, .Longitude = -78.583333, .RecentHighTemperatures = {71, 69, 70, 66, 65, 64, 61}}}
' Add some key/value pairs from multiple threads.
Dim tasks(1) As Task
tasks(0) = Task.Factory.StartNew(Sub()
For i As Integer = 0 To 1
If cities.TryAdd(data(i).Name, data(i)) Then
Console.WriteLine("Added {0} on thread {1}", data(i).Name, Thread.CurrentThread.ManagedThreadId)
Else
Console.WriteLine("Could not add {0}", data(i))
End If
Next
End Sub)
tasks(1) = Task.Factory.StartNew(Sub()
For i As Integer = 2 To data.Length - 1
If cities.TryAdd(data(i).Name, data(i)) Then
Console.WriteLine("Added {0} on thread {1}", data(i).Name, Thread.CurrentThread.ManagedThreadId)
Else
Console.WriteLine("Could not add {0}", data(i))
End If
Next
End Sub)
' Output results so far
Task.WaitAll(tasks)
' Enumerate data on main thread. Note that
' ConcurrentDictionary is the one collection class
' that does not support thread-safe enumeration.
For Each city In cities
Console.WriteLine("{0} has been added", city.Key)
Next
AddOrUpdateWithoutRetrieving()
RetrieveValueOrAdd()
RetrieveAndUpdateOrAdd()
Console.WriteLine("Press any key")
Console.ReadKey()
End Sub
' This method shows how to add key-value pairs to the dictionary
' in scenarios where the key might already exist.
Private Shared Sub AddOrUpdateWithoutRetrieving()
' Sometime later. We receive new data from some source.
Dim ci = New CityInfo With {.Name = "Toronto", .Latitude = 43.716589, .Longitude = -79.340686, .RecentHighTemperatures = {54, 59, 67, 82, 87, 55, -14}}
' Try to add data. If it doesn't exist, the object ci is added. If it does
' already exist, update existingVal according to the custom logic in the
' delegate.
cities.AddOrUpdate(ci.Name, ci, Function(key, existingVal)
' If this delegate is invoked, then the key already exists.
' Here we make sure the city really is the same city we already have.
' (Support for multiple keys of the same name is left as an exercise for the reader.)
If (ci.Name = existingVal.Name And ci.Longitude = existingVal.Longitude) = False Then
Throw New ArgumentException("Duplicate city names are not allowed: {0}.", ci.Name)
End If
' The only updatable fields are the temerature array and lastQueryDate.
existingVal.LastQueryDate = DateTime.Now
existingVal.RecentHighTemperatures = ci.RecentHighTemperatures
Return existingVal
End Function)
' Verify that the dictionary contains the new or updated data.
Console.Write("Most recent high temperatures for {0} are: ", cities(ci.Name).Name)
Dim temps = cities(ci.Name).RecentHighTemperatures
For Each temp In temps
Console.Write("{0}, ", temp)
Next
Console.WriteLine()
End Sub
'This method shows how to use data and ensure that it has been
' added to the dictionary.
Private Shared Sub RetrieveValueOrAdd()
Dim searchKey = "Caracas"
Dim retrievedValue As CityInfo = Nothing
Try
retrievedValue = cities.GetOrAdd(searchKey, GetDataForCity(searchKey))
Catch e As ArgumentException
Console.WriteLine(e.Message)
End Try
' Use the data.
If Not retrievedValue Is Nothing Then
Console.WriteLine("Most recent high temperatures for {0} are: ", retrievedValue.Name)
Dim temps = cities(retrievedValue.Name).RecentHighTemperatures
For Each temp In temps
Console.Write("{0}, ", temp)
Next
End If
Console.WriteLine()
End Sub
' This method shows how to retrieve a value from the dictionary,
' when you expect that the key/value pair already exists,
' and then possibly update the dictionary with a new value for the key.
Private Shared Sub RetrieveAndUpdateOrAdd()
Dim retrievedValue As CityInfo = New CityInfo()
Dim searchKey = "Buenos Aires"
If (cities.TryGetValue(searchKey, retrievedValue)) Then
' Use the data
Console.Write("Most recent high temperatures for {0} are: ", retrievedValue.Name)
Dim temps = retrievedValue.RecentHighTemperatures
For Each temp In temps
Console.Write("{0}, ", temp)
Next
' Make a copy of the data. Our object will update its lastQueryDate automatically.
Dim newValue As CityInfo = New CityInfo(retrievedValue.Name,
retrievedValue.Longitude,
retrievedValue.Latitude,
retrievedValue.RecentHighTemperatures)
Else
Console.WriteLine("Unable to find data for {0}", searchKey)
End If
End Sub
' Assume this method knows how to find long/lat/temp info for any specified city.
Private Shared Function GetDataForCity(ByVal searchKey As String) As CityInfo
' Real implementation left as exercise for the reader.
If String.CompareOrdinal(searchKey, "Caracas") = 0 Then
Return New CityInfo() With {.Name = "Caracas",
.Longitude = 10.5,
.Latitude = -66.916667,
.RecentHighTemperatures = {91, 89, 91, 91, 87, 90, 91}}
ElseIf String.CompareOrdinal(searchKey, "Buenos Aires") = 0 Then
Return New CityInfo() With {.Name = "Buenos Aires",
.Longitude = -34.61,
.Latitude = -58.369997,
.RecentHighTemperatures = {80, 86, 89, 91, 84, 86, 88}}
Else
Throw New ArgumentException("Cannot find any data for {0}", searchKey)
End If
End Function
End Class
End Namespace
namespace DictionaryHowTo
{
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
// The type of the Value to store in the dictionary:
class CityInfo : IEqualityComparer<CityInfo>
{
public string Name { get; set; }
public DateTime lastQueryDate { get; set; }
public decimal Longitude { get; set; }
public decimal Latitude { get; set; }
public int[] RecentHighTemperatures { get; set; }
public CityInfo(string name, decimal longitude, decimal latitude, int[] temps)
{
Name = name;
lastQueryDate = DateTime.Now;
Longitude = longitude;
Latitude = latitude;
RecentHighTemperatures = temps;
}
public CityInfo()
{
}
public CityInfo(string key)
{
Name = key;
// MaxValue means "not initialized"
Longitude = Decimal.MaxValue;
Latitude = Decimal.MaxValue;
lastQueryDate = DateTime.Now;
RecentHighTemperatures = new int[] { 0 };
}
public bool Equals(CityInfo x, CityInfo y)
{
return x.Name == y.Name && x.Longitude == y.Longitude && x.Latitude == y.Latitude;
}
public int GetHashCode(CityInfo obj)
{
CityInfo ci = (CityInfo)obj;
return ci.Name.GetHashCode();
}
}
class Program
{
// Create a new concurrent dictionary.
static ConcurrentDictionary<string, CityInfo> cities = new ConcurrentDictionary<string, CityInfo>();
static void Main(string[] args)
{
CityInfo[] data =
{
new CityInfo(){ Name = "Boston", Latitude = 42.358769M, Longitude = -71.057806M, RecentHighTemperatures = new int[] {56, 51, 52, 58, 65, 56,53}},
new CityInfo(){ Name = "Miami", Latitude = 25.780833M, Longitude = -80.195556M, RecentHighTemperatures = new int[] {86,87,88,87,85,85,86}},
new CityInfo(){ Name = "Los Angeles", Latitude = 34.05M, Longitude = -118.25M, RecentHighTemperatures = new int[] {67,68,69,73,79,78,78}},
new CityInfo(){ Name = "Seattle", Latitude = 47.609722M, Longitude = -122.333056M, RecentHighTemperatures = new int[] {49,50,53,47,52,52,51}},
new CityInfo(){ Name = "Toronto", Latitude = 43.716589M, Longitude = -79.340686M, RecentHighTemperatures = new int[] {53,57, 51,52,56,55,50}},
new CityInfo(){ Name = "Mexico City", Latitude = 19.432736M, Longitude = -99.133253M, RecentHighTemperatures = new int[] {72,68,73,77,76,74,73}},
new CityInfo(){ Name = "Rio de Janiero", Latitude = -22.908333M, Longitude = -43.196389M, RecentHighTemperatures = new int[] {72,68,73,82,84,78,84}},
new CityInfo(){ Name = "Quito", Latitude = -0.25M, Longitude = -78.583333M, RecentHighTemperatures = new int[] {71,69,70,66,65,64,61}}
};
// Add some key/value pairs from multiple threads.
Task[] tasks = new Task[2];
tasks[0] = Task.Factory.StartNew(() =>
{
for (int i = 0; i < 2; i++)
{
if (cities.TryAdd(data[i].Name, data[i]))
Console.WriteLine("Added {0} on thread {1}", data[i],
Thread.CurrentThread.ManagedThreadId);
else
Console.WriteLine("Could not add {0}", data[i]);
}
});
tasks[1] = Task.Factory.StartNew(() =>
{
for (int i = 2; i < data.Length; i++)
{
if (cities.TryAdd(data[i].Name, data[i]))
Console.WriteLine("Added {0} on thread {1}", data[i],
Thread.CurrentThread.ManagedThreadId);
else
Console.WriteLine("Could not add {0}", data[i]);
}
});
// Output results so far.
Task.WaitAll(tasks);
// Enumerate collection from the app main thread.
// Note that ConcurrentDictionary is the one concurrent collection
// that does not support thread-safe enumeration.
foreach (var city in cities)
{
Console.WriteLine("{0} has been added.", city.Key);
}
AddOrUpdateWithoutRetrieving();
RetrieveValueOrAdd();
RetrieveAndUpdateOrAdd();
Console.WriteLine("Press any key.");
Console.ReadKey();
}
// This method shows how to add key-value pairs to the dictionary
// in scenarios where the key might already exist.
private static void AddOrUpdateWithoutRetrieving()
{
// Sometime later. We receive new data from some source.
CityInfo ci = new CityInfo() { Name = "Toronto",
Latitude = 43.716589M,
Longitude = -79.340686M,
RecentHighTemperatures = new int[] { 54, 59, 67, 82, 87, 55, -14 } };
// Try to add data. If it doesn't exist, the object ci is added. If it does
// already exist, update existingVal according to the custom logic in the
// delegate.
cities.AddOrUpdate(ci.Name, ci,
(key, existingVal) =>
{
// If this delegate is invoked, then the key already exists.
// Here we make sure the city really is the same city we already have.
// (Support for multiple cities of the same name is left as an exercise for the reader.)
if (ci != existingVal)
throw new ArgumentException("Duplicate city names are not allowed: {0}.", ci.Name);
// The only updatable fields are the temerature array and lastQueryDate.
existingVal.lastQueryDate = DateTime.Now;
existingVal.RecentHighTemperatures = ci.RecentHighTemperatures;
return existingVal;
});
// Verify that the dictionary contains the new or updated data.
Console.Write("Most recent high temperatures for {0} are: ", cities[ci.Name].Name);
int[] temps = cities[ci.Name].RecentHighTemperatures;
foreach (var temp in temps) Console.Write("{0}, ", temp);
Console.WriteLine();
}
// This method shows how to use data and ensure that it has been
// added to the dictionary.
private static void RetrieveValueOrAdd()
{
string searchKey = "Caracas";
CityInfo retrievedValue = null;
try
{
retrievedValue = cities.GetOrAdd(searchKey, GetDataForCity(searchKey));
}
catch (ArgumentException e)
{
Console.WriteLine(e.Message);
}
// Use the data.
if (retrievedValue != null)
{
Console.Write("Most recent high temperatures for {0} are: ", retrievedValue.Name);
int[] temps = cities[retrievedValue.Name].RecentHighTemperatures;
foreach (var temp in temps) Console.Write("{0}, ", temp);
}
Console.WriteLine();
}
// This method shows how to retrieve a value from the dictionary,
// when you expect that the key/value pair already exists,
// and then possibly update the dictionary with a new value for the key.
private static void RetrieveAndUpdateOrAdd()
{
CityInfo retrievedValue;
string searchKey = "Buenos Aires";
if (cities.TryGetValue(searchKey, out retrievedValue))
{
// use the data
Console.Write("Most recent high temperatures for {0} are: ", retrievedValue.Name);
int[] temps = retrievedValue.RecentHighTemperatures;
foreach (var temp in temps) Console.Write("{0}, ", temp);
// Make a copy of the data. Our object will update its lastQueryDate automatically.
CityInfo newValue = new CityInfo(retrievedValue.Name,
retrievedValue.Longitude,
retrievedValue.Latitude,
retrievedValue.RecentHighTemperatures);
// Replace the old value with the new value.
if (!cities.TryUpdate(searchKey, retrievedValue, newValue))
{
//The data was not updated. Log error, throw exception, etc.
Console.WriteLine("Could not update {0}", retrievedValue.Name);
}
}
else
{
// Add the new key and value. Here we call a method to retrieve
// the data. Another option is to add a default value here and
// update with real data later on some other thread.
CityInfo newValue = GetDataForCity(searchKey);
if( cities.TryAdd(searchKey, newValue))
{
// use the data
Console.Write("Most recent high temperatures for {0} are: ", newValue.Name);
int[] temps = newValue.RecentHighTemperatures;
foreach (var temp in temps) Console.Write("{0}, ", temp);
}
else
Console.WriteLine("Unable to add data for {0}", searchKey);
}
}
//Assume this method knows how to find long/lat/temp info for any specified city.
static CityInfo GetDataForCity(string name)
{
// Real implementation left as exercise for the reader.
if (String.CompareOrdinal(name, "Caracas") == 0)
return new CityInfo() { Name = "Caracas",
Longitude = 10.5M,
Latitude = -66.916667M,
RecentHighTemperatures = new int[] { 91, 89, 91, 91, 87, 90, 91 } };
else if (String.CompareOrdinal(name, "Buenos Aires") == 0)
return new CityInfo() { Name = "Buenos Aires",
Longitude = -34.61M,
Latitude = -58.369997M,
RecentHighTemperatures = new int[] { 80, 86, 89, 91, 84, 86, 88 } };
else
throw new ArgumentException("Cannot find any data for {0}", name);
}
}
}
ConcurrentDictionary<TKey, TValue>는 다중 스레드 시나리오에 맞게 디자인되어 있습니다. 이 컬렉션의 항목을 추가하거나 제거하기 위해 코드에서 잠금을 사용할 필요는 없습니다. 그러나 특정 스레드가 값을 검색하는 즉시 다른 스레드에서 동일한 키에 새 값을 지정하여 컬렉션을 업데이트하는 것은 항상 가능합니다.
또한 ConcurrentDictionary<TKey, TValue>의 모든 메서드가 스레드로부터 안전하지만 모든 메서드가 원자성 메서드인 것은 아닙니다. 특히 GetOrAdd 및 AddOrUpdate는 원자성 메서드가 아닙니다. 이러한 메서드에 전달되는 사용자 대리자는 사전의 내부 잠금 외부에서 호출됩니다. 이렇게 하는 이유는 알려지지 않은 코드가 모든 스레드를 차단하지 않도록 방지하기 위해서입니다. 따라서 다음과 같은 이벤트 시퀀스가 발생할 수 있습니다.
1) threadA가 GetOrAdd를 호출하고, 항목을 찾지 못한 다음, valueFactory 대리자를 호출하여 추가할 새 항목을 만듭니다.
2) threadB가 GetOrAdd를 동시에 호출하고 해당 valueFactory 대리자가 호출되어 threadA보다 먼저 내부 잠금에 도달하므로 threadB의 새 키-값 쌍이 사전에 추가됩니다.
3) threadA의 사용자 대리자가 완료되고 스레드가 잠금에 도달하지만 이제는 해당 항목이 이미 존재하는 것으로 표시됩니다.
4) threadA가 "Get"을 수행하고 이전에 threadB에 의해 추가된 데이터를 반환합니다.
따라서 GetOrAdd로 반환된 데이터가 스레드의 valueFactory로 만들어진 것과 동일한 데이터라고 보증할 수 없습니다. AddOrUpdate를 호출할 때에도 비슷한 이벤트 시퀀스가 발생할 수 있습니다.