Semaphore 构造函数

定义

命名空间:

System.Threading

程序集:

System.Threading.dll

初始化 Semaphore 类的新实例。

重载

Semaphore(Int32, Int32)	初始化 Semaphore 类的新实例，并指定初始入口数和最大并发入口数。
Semaphore(Int32, Int32, String)	初始化 Semaphore 类的新实例，并指定初始入口数和最大并发入口数，可以选择指定系统信号量对象的名称。
Semaphore(Int32, Int32, String, Boolean)	初始化 Semaphore 类的新实例，并指定初始入口数和最大并发入口数，还可以选择指定系统信号量对象的名称，以及指定一个变量来接收指示是否创建了新系统信号量的值。

Semaphore(Int32, Int32)

Source:

Semaphore.cs

初始化 Semaphore 类的新实例，并指定初始入口数和最大并发入口数。

public:
 Semaphore(int initialCount, int maximumCount);

public Semaphore (int initialCount, int maximumCount);

new System.Threading.Semaphore : int * int -> System.Threading.Semaphore

Public Sub New (initialCount As Integer, maximumCount As Integer)

参数

initialCount

Int32

可以同时授予的信号量的初始请求数。

maximumCount

Int32

可以同时授予的信号量的最大请求数。

例外

ArgumentException

initialCount 大于 maximumCount。

ArgumentOutOfRangeException

maximumCount 小于 1。

或

initialCount 小于 0。

示例

以下示例创建一个信号灯，其最大计数为 3，初始计数为零。 该示例启动五个线程，这些线程阻止等待信号灯。 main线程使用 Release(Int32) 方法重载将信号量增加到最大值，允许三个线程进入信号量。 每个线程使用 Thread.Sleep 方法等待一秒钟，以模拟工作，然后调用 Release() 方法重载以释放信号量。 每次释放信号灯时，都会显示以前的信号量计数。 控制台消息跟踪信号灯使用情况。 每个线程的模拟工作间隔会略有增加，使输出更易于读取。

#using <System.dll>
using namespace System;
using namespace System::Threading;

public ref class Example
{
private:
   // A semaphore that simulates a limited resource pool.
   //
   static Semaphore^ _pool;

   // A padding interval to make the output more orderly.
   static int _padding;

public:
   static void Main()
   {
      // Create a semaphore that can satisfy up to three
      // concurrent requests. Use an initial count of zero,
      // so that the entire semaphore count is initially
      // owned by the main program thread.
      //
      _pool = gcnew Semaphore( 0,3 );
      
      // Create and start five numbered threads.
      //
      for ( int i = 1; i <= 5; i++ )
      {
         Thread^ t = gcnew Thread(
            gcnew ParameterizedThreadStart( Worker ) );
         
         // Start the thread, passing the number.
         //
         t->Start( i );
      }
      
      // Wait for half a second, to allow all the
      // threads to start and to block on the semaphore.
      //
      Thread::Sleep( 500 );
      
      // The main thread starts out holding the entire
      // semaphore count. Calling Release(3) brings the
      // semaphore count back to its maximum value, and
      // allows the waiting threads to enter the semaphore,
      // up to three at a time.
      //
      Console::WriteLine( L"Main thread calls Release(3)." );
      _pool->Release( 3 );

      Console::WriteLine( L"Main thread exits." );
   }

private:
   static void Worker( Object^ num )
   {
      // Each worker thread begins by requesting the
      // semaphore.
      Console::WriteLine( L"Thread {0} begins and waits for the semaphore.", num );
      _pool->WaitOne();
      
      // A padding interval to make the output more orderly.
      int padding = Interlocked::Add( _padding, 100 );

      Console::WriteLine( L"Thread {0} enters the semaphore.", num );
      
      // The thread's "work" consists of sleeping for
      // about a second. Each thread "works" a little
      // longer, just to make the output more orderly.
      //
      Thread::Sleep( 1000 + padding );

      Console::WriteLine( L"Thread {0} releases the semaphore.", num );
      Console::WriteLine( L"Thread {0} previous semaphore count: {1}",
         num, _pool->Release() );
   }
};

using System;
using System.Threading;

public class Example
{
    // A semaphore that simulates a limited resource pool.
    //
    private static Semaphore _pool;

    // A padding interval to make the output more orderly.
    private static int _padding;

    public static void Main()
    {
        // Create a semaphore that can satisfy up to three
        // concurrent requests. Use an initial count of zero,
        // so that the entire semaphore count is initially
        // owned by the main program thread.
        //
        _pool = new Semaphore(initialCount: 0, maximumCount: 3);

        // Create and start five numbered threads. 
        //
        for(int i = 1; i <= 5; i++)
        {
            Thread t = new Thread(new ParameterizedThreadStart(Worker));

            // Start the thread, passing the number.
            //
            t.Start(i);
        }

        // Wait for half a second, to allow all the
        // threads to start and to block on the semaphore.
        //
        Thread.Sleep(500);

        // The main thread starts out holding the entire
        // semaphore count. Calling Release(3) brings the 
        // semaphore count back to its maximum value, and
        // allows the waiting threads to enter the semaphore,
        // up to three at a time.
        //
        Console.WriteLine("Main thread calls Release(3).");
        _pool.Release(releaseCount: 3);

        Console.WriteLine("Main thread exits.");
    }

    private static void Worker(object num)
    {
        // Each worker thread begins by requesting the
        // semaphore.
        Console.WriteLine("Thread {0} begins " +
            "and waits for the semaphore.", num);
        _pool.WaitOne();

        // A padding interval to make the output more orderly.
        int padding = Interlocked.Add(ref _padding, 100);

        Console.WriteLine("Thread {0} enters the semaphore.", num);
        
        // The thread's "work" consists of sleeping for 
        // about a second. Each thread "works" a little 
        // longer, just to make the output more orderly.
        //
        Thread.Sleep(1000 + padding);

        Console.WriteLine("Thread {0} releases the semaphore.", num);
        Console.WriteLine("Thread {0} previous semaphore count: {1}",
            num, _pool.Release());
    }
}

Imports System.Threading

Public Class Example

    ' A semaphore that simulates a limited resource pool.
    '
    Private Shared _pool As Semaphore

    ' A padding interval to make the output more orderly.
    Private Shared _padding As Integer

    <MTAThread> _
    Public Shared Sub Main()
        ' Create a semaphore that can satisfy up to three
        ' concurrent requests. Use an initial count of zero,
        ' so that the entire semaphore count is initially
        ' owned by the main program thread.
        '
        _pool = New Semaphore(0, 3)

        ' Create and start five numbered threads. 
        '
        For i As Integer = 1 To 5
            Dim t As New Thread(New ParameterizedThreadStart(AddressOf Worker))
            'Dim t As New Thread(AddressOf Worker)

            ' Start the thread, passing the number.
            '
            t.Start(i)
        Next i

        ' Wait for half a second, to allow all the
        ' threads to start and to block on the semaphore.
        '
        Thread.Sleep(500)

        ' The main thread starts out holding the entire
        ' semaphore count. Calling Release(3) brings the 
        ' semaphore count back to its maximum value, and
        ' allows the waiting threads to enter the semaphore,
        ' up to three at a time.
        '
        Console.WriteLine("Main thread calls Release(3).")
        _pool.Release(3)

        Console.WriteLine("Main thread exits.")
    End Sub

    Private Shared Sub Worker(ByVal num As Object)
        ' Each worker thread begins by requesting the
        ' semaphore.
        Console.WriteLine("Thread {0} begins " _
            & "and waits for the semaphore.", num)
        _pool.WaitOne()

        ' A padding interval to make the output more orderly.
        Dim padding As Integer = Interlocked.Add(_padding, 100)

        Console.WriteLine("Thread {0} enters the semaphore.", num)
        
        ' The thread's "work" consists of sleeping for 
        ' about a second. Each thread "works" a little 
        ' longer, just to make the output more orderly.
        '
        Thread.Sleep(1000 + padding)

        Console.WriteLine("Thread {0} releases the semaphore.", num)
        Console.WriteLine("Thread {0} previous semaphore count: {1}", _
            num, _
            _pool.Release())
    End Sub
End Class

注解

此构造函数初始化未命名的信号灯。 使用此类信号灯实例的所有线程都必须具有对该实例的引用。

如果 initialCount 小于 maximumCount，则效果与当前线程调用 WaitOne (maximumCount 减) initialCount 次相同。 如果不想为创建信号灯的线程保留任何条目，请为 maximumCount 和 initialCount使用相同的数字。

另请参阅

• 托管线程
• Semaphore

Semaphore(Int32, Int32, String)

Source:

Semaphore.cs

初始化 Semaphore 类的新实例，并指定初始入口数和最大并发入口数，可以选择指定系统信号量对象的名称。

public:
 Semaphore(int initialCount, int maximumCount, System::String ^ name);

public Semaphore (int initialCount, int maximumCount, string? name);

new System.Threading.Semaphore : int * int * string -> System.Threading.Semaphore

Public Sub New (initialCount As Integer, maximumCount As Integer, name As String)

参数

initialCount

Int32

可以同时授予的信号量的初始请求数。

maximumCount

Int32

可以同时授予的信号量的最大请求数。

name

String

如果要与其他进程共享同步对象，则为名称；否则为 null 或空字符串。 该名称区分大小写。 反斜杠字符 (\) 是保留的，只能用于指定命名空间。 有关命名空间的详细信息，请参阅备注部分。 根据操作系统，名称可能会有进一步的限制。 例如，在基于 Unix 的操作系统上，排除命名空间后的名称必须是有效的文件名。

例外

ArgumentException

initialCount 大于 maximumCount。

或

仅限 .NET Framework：name 的长度超过 MAX_PATH（260 个字符）。

ArgumentOutOfRangeException

maximumCount 小于 1。

或

initialCount 小于 0。

IOException

name 无效。 导致这种情况的原因有很多，包括操作系统可能会施加的一些限制，例如未知前缀或无效字符。 请注意，名称和通用前缀“Global\”和“Local\”区分大小写。

或

还有一些其他错误。 HResult 属性可能提供更多信息。

DirectoryNotFoundException

仅限 Windows：name 指定了未知命名空间。 有关详细信息，请参阅对象名称。

PathTooLongException

name 太长。 长度限制可能取决于操作系统或配置。

UnauthorizedAccessException

命名信号量存在且具有访问控制安全性，用户不具有 FullControl。

WaitHandleCannotBeOpenedException

无法创建具有提供的 name 的同步对象。 不同类型的同步对象可能具有相同的名称。

示例

下面的代码示例演示命名信号灯的跨进程行为。 该示例创建一个命名信号灯，其最大计数为 5，初始计数为 5。 程序对 方法进行三次调用 WaitOne 。 因此，如果从两个命令窗口运行编译的示例，第二个副本将在第三次调用 WaitOne时阻止。 释放程序第一个副本中的一个或多个条目以取消阻止第二个。

#using <System.dll>
using namespace System;
using namespace System::Threading;

public ref class Example
{
public:
   static void main()
   {
      // Create a Semaphore object that represents the named
      // system semaphore "SemaphoreExample3". The semaphore has a
      // maximum count of five. The initial count is also five.
      // There is no point in using a smaller initial count,
      // because the initial count is not used if this program
      // doesn't create the named system semaphore, and with
      // this method overload there is no way to tell. Thus, this
      // program assumes that it is competing with other
      // programs for the semaphore.
      //
      Semaphore^ sem = gcnew Semaphore( 5,5,L"SemaphoreExample3" );
      
      // Attempt to enter the semaphore three times. If another
      // copy of this program is already running, only the first
      // two requests can be satisfied. The third blocks. Note
      // that in a real application, timeouts should be used
      // on the WaitOne calls, to avoid deadlocks.
      //
      sem->WaitOne();
      Console::WriteLine( L"Entered the semaphore once." );
      sem->WaitOne();
      Console::WriteLine( L"Entered the semaphore twice." );
      sem->WaitOne();
      Console::WriteLine( L"Entered the semaphore three times." );
      
      // The thread executing this program has entered the
      // semaphore three times. If a second copy of the program
      // is run, it will block until this program releases the
      // semaphore at least once.
      //
      Console::WriteLine( L"Enter the number of times to call Release." );
      int n;
      if ( Int32::TryParse( Console::ReadLine(),n ) )
      {
         sem->Release( n );
      }

      int remaining = 3 - n;
      if ( remaining > 0 )
      {
         Console::WriteLine( L"Press Enter to release the remaining "
         L"count ({0}) and exit the program.", remaining );
         Console::ReadLine();
         sem->Release( remaining );
      }
   }
};

using System;
using System.Threading;

public class Example
{
    public static void Main()
    {
        // Create a Semaphore object that represents the named 
        // system semaphore "SemaphoreExample3". The semaphore has a
        // maximum count of five. The initial count is also five. 
        // There is no point in using a smaller initial count,
        // because the initial count is not used if this program
        // doesn't create the named system semaphore, and with 
        // this method overload there is no way to tell. Thus, this
        // program assumes that it is competing with other
        // programs for the semaphore.
        //
        Semaphore sem = new Semaphore(5, 5, "SemaphoreExample3");

        // Attempt to enter the semaphore three times. If another 
        // copy of this program is already running, only the first
        // two requests can be satisfied. The third blocks. Note 
        // that in a real application, timeouts should be used
        // on the WaitOne calls, to avoid deadlocks.
        //
        sem.WaitOne();
        Console.WriteLine("Entered the semaphore once.");
        sem.WaitOne();
        Console.WriteLine("Entered the semaphore twice.");
        sem.WaitOne();
        Console.WriteLine("Entered the semaphore three times.");

        // The thread executing this program has entered the 
        // semaphore three times. If a second copy of the program
        // is run, it will block until this program releases the 
        // semaphore at least once.
        //
        Console.WriteLine("Enter the number of times to call Release.");
        int n;
        if (int.TryParse(Console.ReadLine(), out n))
        {
            sem.Release(n);
        }

        int remaining = 3 - n;
        if (remaining > 0)
        {
            Console.WriteLine("Press Enter to release the remaining " +
                "count ({0}) and exit the program.", remaining);
            Console.ReadLine();
            sem.Release(remaining);
        }
    }
}

Imports System.Threading

Public Class Example

    <MTAThread> _
    Public Shared Sub Main()
        ' Create a Semaphore object that represents the named 
        ' system semaphore "SemaphoreExample3". The semaphore has a
        ' maximum count of five. The initial count is also five. 
        ' There is no point in using a smaller initial count,
        ' because the initial count is not used if this program
        ' doesn't create the named system semaphore, and with 
        ' this method overload there is no way to tell. Thus, this
        ' program assumes that it is competing with other
        ' programs for the semaphore.
        '
        Dim sem As New Semaphore(5, 5, "SemaphoreExample3")

        ' Attempt to enter the semaphore three times. If another 
        ' copy of this program is already running, only the first
        ' two requests can be satisfied. The third blocks. Note 
        ' that in a real application, timeouts should be used
        ' on the WaitOne calls, to avoid deadlocks.
        '
        sem.WaitOne()
        Console.WriteLine("Entered the semaphore once.")
        sem.WaitOne()
        Console.WriteLine("Entered the semaphore twice.")
        sem.WaitOne()
        Console.WriteLine("Entered the semaphore three times.")

        ' The thread executing this program has entered the 
        ' semaphore three times. If a second copy of the program
        ' is run, it will block until this program releases the 
        ' semaphore at least once.
        '
        Console.WriteLine("Enter the number of times to call Release.")
        Dim n As Integer
        If Integer.TryParse(Console.ReadLine(), n) Then
            sem.Release(n)
        End If

        Dim remaining As Integer = 3 - n
        If (remaining) > 0 Then
            Console.WriteLine("Press Enter to release the remaining " _
                & "count ({0}) and exit the program.", remaining)
            Console.ReadLine()
            sem.Release(remaining)
        End If

    End Sub 
End Class

注解

此构造函数初始化一个 Semaphore 对象，该对象表示命名的系统信号量。 可以创建表示同一命名系统信号量的多个 Semaphore 对象。

name可以使用 或 Local\ 作为Global\前缀，以指定命名空间。 Global指定命名空间后，可以与系统上的任何进程共享同步对象。 Local指定命名空间时（未指定命名空间时也是默认值），可以与同一会话中的进程共享同步对象。 在 Windows 上，会话是登录会话，服务通常在不同的非交互式会话中运行。 在类似于 Unix 的操作系统上，每个 shell 都有其自己的会话。 会话本地同步对象可能适合用于使用父/子关系（在这些进程都在同一会话中运行）之间进行同步。 有关 Windows 上的同步对象名称的详细信息，请参阅 对象名称。

如果提供了 ， name 并且命名空间中已存在所请求类型的同步对象，则使用现有同步对象。 如果命名空间中已存在不同类型的同步对象， WaitHandleCannotBeOpenedException 则会引发 。 否则，将创建新的同步对象。

如果命名的系统信号量不存在，则会使用 和 maximumCount指定的initialCount初始计数和最大计数来创建它。 如果命名的系统信号量已存在且 initialCountmaximumCount 未使用，但无效值仍会导致异常。 如果需要确定是否创建了命名系统信号量，请改用 Semaphore(Int32, Int32, String, Boolean) 构造函数重载。

重要

使用此构造函数重载时，建议的做法是为 和 maximumCount指定相同的数字initialCount。 如果 initialCount 小于 maximumCount，并且创建了命名的系统信号量，则效果与当前线程调用 WaitOne (maximumCount 减去 initialCount) 次相同。 但是，对于此构造函数重载，无法确定是否创建了命名系统信号量。

如果为 name指定null或空字符串，则会创建本地信号量，就像调用Semaphore(Int32, Int32)构造函数重载一样。

由于命名信号灯在整个操作系统中可见，因此它们可用于跨进程边界协调资源使用。

如果要了解命名系统信号量是否存在，请使用 OpenExisting 方法。 方法 OpenExisting 尝试打开现有的命名信号灯，如果系统信号量不存在，则引发异常。

注意

默认情况下，命名信号量不仅限于创建它的用户。 其他用户可能能够打开和使用信号灯，包括通过多次获取信号灯而不释放信号灯来干扰信号量。 若要限制对特定用户的访问，可以在创建命名信号量时使用构造函数重载或 SemaphoreAcl 并传入 SemaphoreSecurity 。 避免在没有访问限制的情况下使用命名信号灯，这些信号灯对可能具有不受信任的用户运行代码的系统。

另请参阅

• 托管线程
• Semaphore

Semaphore(Int32, Int32, String, Boolean)

Source:

Semaphore.cs

初始化 Semaphore 类的新实例，并指定初始入口数和最大并发入口数，还可以选择指定系统信号量对象的名称，以及指定一个变量来接收指示是否创建了新系统信号量的值。

public:
 Semaphore(int initialCount, int maximumCount, System::String ^ name, [Runtime::InteropServices::Out] bool % createdNew);

public Semaphore (int initialCount, int maximumCount, string? name, out bool createdNew);

new System.Threading.Semaphore : int * int * string * bool -> System.Threading.Semaphore

Public Sub New (initialCount As Integer, maximumCount As Integer, name As String, ByRef createdNew As Boolean)

参数

initialCount

Int32

可以同时满足的信号量的初始请求数。

maximumCount

Int32

可以同时满足的信号量的最大请求数。

name

String

如果要与其他进程共享同步对象，则为名称；否则为 null 或空字符串。 该名称区分大小写。 反斜杠字符 (\) 是保留的，只能用于指定命名空间。 有关命名空间的详细信息，请参阅备注部分。 根据操作系统，名称可能会有进一步的限制。 例如，在基于 Unix 的操作系统上，排除命名空间后的名称必须是有效的文件名。

createdNew

Boolean

在此方法返回时，如果创建了本地信号量（即，如果 name 为 null 或空字符串）或指定的命名系统信号量，则包含 true；如果指定的命名系统信号量已存在，则为 false。 此参数未经初始化即被传递。

例外

ArgumentException

initialCount 大于 maximumCount。

或

仅限 .NET Framework：name 的长度超过 MAX_PATH（260 个字符）。

ArgumentOutOfRangeException

maximumCount 小于 1。

或

initialCount 小于 0。

IOException

name 无效。 导致这种情况的原因有很多，包括操作系统可能会施加的一些限制，例如未知前缀或无效字符。 请注意，名称和通用前缀“Global\”和“Local\”区分大小写。

或

还有一些其他错误。 HResult 属性可能提供更多信息。

DirectoryNotFoundException

仅限 Windows：name 指定了未知命名空间。 有关详细信息，请参阅对象名称。

PathTooLongException

name 太长。 长度限制可能取决于操作系统或配置。

UnauthorizedAccessException

命名信号量存在且具有访问控制安全性，用户不具有 FullControl。

WaitHandleCannotBeOpenedException

无法创建具有提供的 name 的同步对象。 不同类型的同步对象可能具有相同的名称。

示例

下面的代码示例演示命名信号灯的跨进程行为。 该示例创建一个命名信号灯，其最大计数为 5，初始计数为 2。 也就是说，它为调用构造函数的线程保留三个条目。 如果 createNew 为 false，则程序对 WaitOne 方法进行三次调用。 因此，如果从两个命令窗口运行编译的示例，第二个副本将在第三次调用 WaitOne时阻止。 释放程序第一个副本中的一个或多个条目以取消阻止第二个。

#using <System.dll>
using namespace System;
using namespace System::Threading;

public ref class Example
{
public:
   static void main()
   {
      // The value of this variable is set by the semaphore
      // constructor. It is true if the named system semaphore was
      // created, and false if the named semaphore already existed.
      //
      bool semaphoreWasCreated;
      
      // Create a Semaphore object that represents the named
      // system semaphore "SemaphoreExample". The semaphore has a
      // maximum count of five, and an initial count of two. The
      // Boolean value that indicates creation of the underlying
      // system object is placed in semaphoreWasCreated.
      //
      Semaphore^ sem = gcnew Semaphore( 2,5,L"SemaphoreExample",
         semaphoreWasCreated );
      if ( semaphoreWasCreated )
      {
         // If the named system semaphore was created, its count is
         // set to the initial count requested in the constructor.
         // In effect, the current thread has entered the semaphore
         // three times.
         //
         Console::WriteLine( L"Entered the semaphore three times." );
      }
      else
      {
         // If the named system semaphore was not created,
         // attempt to enter it three times. If another copy of
         // this program is already running, only the first two
         // requests can be satisfied. The third blocks.
         //
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore once." );
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore twice." );
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore three times." );
      }
      
      // The thread executing this program has entered the
      // semaphore three times. If a second copy of the program
      // is run, it will block until this program releases the
      // semaphore at least once.
      //
      Console::WriteLine( L"Enter the number of times to call Release." );
      int n;
      if ( Int32::TryParse( Console::ReadLine(), n ) )
      {
         sem->Release( n );
      }

      int remaining = 3 - n;
      if ( remaining > 0 )
      {
         Console::WriteLine( L"Press Enter to release the remaining "
         L"count ({0}) and exit the program.", remaining );
         Console::ReadLine();
         sem->Release( remaining );
      }
   }
};

using System;
using System.Threading;

public class Example
{
    public static void Main()
    {
        // The value of this variable is set by the semaphore
        // constructor. It is true if the named system semaphore was
        // created, and false if the named semaphore already existed.
        //
        bool semaphoreWasCreated;

        // Create a Semaphore object that represents the named 
        // system semaphore "SemaphoreExample". The semaphore has a
        // maximum count of five, and an initial count of two. The
        // Boolean value that indicates creation of the underlying 
        // system object is placed in semaphoreWasCreated.
        //
        Semaphore sem = new Semaphore(2, 5, "SemaphoreExample", 
            out semaphoreWasCreated);

        if (semaphoreWasCreated)
        {
            // If the named system semaphore was created, its count is
            // set to the initial count requested in the constructor.
            // In effect, the current thread has entered the semaphore
            // three times.
            // 
            Console.WriteLine("Entered the semaphore three times.");
        }
        else
        {      
            // If the named system semaphore was not created,  
            // attempt to enter it three times. If another copy of
            // this program is already running, only the first two
            // requests can be satisfied. The third blocks.
            //
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore once.");
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore twice.");
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore three times.");
        }

        // The thread executing this program has entered the 
        // semaphore three times. If a second copy of the program
        // is run, it will block until this program releases the 
        // semaphore at least once.
        //
        Console.WriteLine("Enter the number of times to call Release.");
        int n;
        if (int.TryParse(Console.ReadLine(), out n))
        {
            sem.Release(n);
        }

        int remaining = 3 - n;
        if (remaining > 0)
        {
            Console.WriteLine("Press Enter to release the remaining " +
                "count ({0}) and exit the program.", remaining);
            Console.ReadLine();
            sem.Release(remaining);
        }
    } 
}

Imports System.Threading

Public Class Example

    <MTAThread> _
    Public Shared Sub Main()
        ' The value of this variable is set by the semaphore
        ' constructor. It is True if the named system semaphore was
        ' created, and False if the named semaphore already existed.
        '
        Dim semaphoreWasCreated As Boolean

        ' Create a Semaphore object that represents the named 
        ' system semaphore "SemaphoreExample". The semaphore has a
        ' maximum count of five, and an initial count of two. The
        ' Boolean value that indicates creation of the underlying 
        ' system object is placed in semaphoreWasCreated.
        '
        Dim sem As New Semaphore(2, 5, "SemaphoreExample", _
            semaphoreWasCreated)

        If semaphoreWasCreated Then
            ' If the named system semaphore was created, its count is
            ' set to the initial count requested in the constructor.
            ' In effect, the current thread has entered the semaphore
            ' three times.
            ' 
            Console.WriteLine("Entered the semaphore three times.")
        Else
            ' If the named system semaphore was not created,  
            ' attempt to enter it three times. If another copy of
            ' this program is already running, only the first two
            ' requests can be satisfied. The third blocks.
            '
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore once.")
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore twice.")
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore three times.")
        End If

        ' The thread executing this program has entered the 
        ' semaphore three times. If a second copy of the program
        ' is run, it will block until this program releases the 
        ' semaphore at least once.
        '
        Console.WriteLine("Enter the number of times to call Release.")
        Dim n As Integer
        If Integer.TryParse(Console.ReadLine(), n) Then
            sem.Release(n)
        End If

        Dim remaining As Integer = 3 - n
        If (remaining) > 0 Then
            Console.WriteLine("Press Enter to release the remaining " _
                & "count ({0}) and exit the program.", remaining)
            Console.ReadLine()
            sem.Release(remaining)
        End If

    End Sub 
End Class

注解

name可以使用 或 Local\ 作为Global\前缀，以指定命名空间。 Global指定命名空间后，可以与系统上的任何进程共享同步对象。 Local指定命名空间时（未指定命名空间时也是默认值），可以与同一会话中的进程共享同步对象。 在 Windows 上，会话是登录会话，服务通常在不同的非交互式会话中运行。 在类似于 Unix 的操作系统上，每个 shell 都有其自己的会话。 会话本地同步对象可能适合用于使用父/子关系（在这些进程都在同一会话中运行）之间进行同步。 有关 Windows 上的同步对象名称的详细信息，请参阅 对象名称。

如果提供了 ， name 并且命名空间中已存在所请求类型的同步对象，则使用现有同步对象。 如果命名空间中已存在不同类型的同步对象， WaitHandleCannotBeOpenedException 则会引发 。 否则，将创建新的同步对象。

此构造函数初始化一个 Semaphore 对象，该对象表示命名的系统信号量。 可以创建表示同一命名系统信号量的多个 Semaphore 对象。

如果命名的系统信号量不存在，则会使用 和 maximumCount指定的initialCount初始计数和最大计数来创建它。 如果命名的系统信号量已存在且 initialCountmaximumCount 未使用，但无效值仍会导致异常。 使用 createdNew 确定是否创建了系统信号灯。

如果 initialCount 小于 maximumCount，且 createdNew 为 true，则效果与当前线程调用 WaitOne (maximumCount 减去 initialCount) 次相同。

如果为 name指定null或空字符串，则会创建本地信号量，就像调用Semaphore(Int32, Int32)构造函数重载一样。 在这种情况下， createdNew 始终 true为 。

由于命名信号灯在整个操作系统中可见，因此它们可用于跨进程边界协调资源使用。

注意

默认情况下，命名信号量不仅限于创建它的用户。 其他用户可能能够打开和使用信号灯，包括通过多次获取信号灯而不释放信号灯来干扰信号量。 若要限制对特定用户的访问，可以在创建命名信号量时使用构造函数重载或 SemaphoreAcl 并传入 SemaphoreSecurity 。 避免在没有访问限制的情况下使用命名信号灯，这些信号灯对可能具有不受信任的用户运行代码的系统。

另请参阅

• 托管线程
• Semaphore