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SemaphoreFullException Class

Note: This class is new in the .NET Framework version 2.0.

The exception that is thrown when the System.Threading.Semaphore.Release method is called on a semaphore whose count is already at the maximum.

Namespace: System.Threading
Assembly: System (in system.dll)

'Declaration
<SerializableAttribute> _
<ComVisibleAttribute(False)> _
Public Class SemaphoreFullException
	Inherits SystemException
'Usage
Dim instance As SemaphoreFullException

/** @attribute SerializableAttribute() */ 
/** @attribute ComVisibleAttribute(false) */ 
public class SemaphoreFullException extends SystemException
SerializableAttribute 
ComVisibleAttribute(false) 
public class SemaphoreFullException extends SystemException

The count on a semaphore is decremented each time a thread enters the semaphore, and incremented when a thread releases the semaphore. When the count is zero, subsequent requests block until other threads release the semaphore. When all threads have released the semaphore, the count is at the maximum value specified when the semaphore was created. If a programming error causes a thread to call the System.Threading.Semaphore.Release method at this point, a SemaphoreFullException is thrown.

NoteNote

The Semaphore class does not enforce thread identity on calls to the System.Threading.WaitHandle.WaitOne and System.Threading.Semaphore.Release methods. It is not necessary for the same thread that called WaitOne to call Release.

SemaphoreFullException does not necessarily indicate a problem with the code where the exception occurred. Consider the following scenario: Thread A and thread B enter a semaphore that has a maximum count of two. A programming error in thread B causes it to call Release twice, so that the count on the semaphore is full. As a result, when thread A eventually calls Release, a SemaphoreFullException is thrown.

For a list of initial property values for an instance of the SemaphoreFullException class, see the SemaphoreFullException constructor.

The following code example shows how a programming error in one thread can lead to a SemaphoreFullException in another thread: Two threads enter a semaphore. The second thread releases the semaphore twice, while the first thread is still executing its task. When the first thread finishes and releases the semaphore, the semaphore count is already full and an exception is thrown.

Imports System
Imports System.Threading

Public Class Example

    ' A semaphore that can satisfy at most two concurrent
    ' requests.
    '
    Private Shared _pool As New Semaphore(2, 2)

    <MTAThread> _
    Public Shared Sub Main()
        ' Create and start two threads, A and B. 
        '
        Dim tA As New Thread(AddressOf ThreadA)
        tA.Start()

        Dim tB As New Thread(AddressOf ThreadB)
        tB.Start()

    End Sub

    Private Shared Sub ThreadA()
        ' Thread A enters the semaphore and simulates a task
        ' that lasts a second.
        '
        _pool.WaitOne()
        Console.WriteLine("Thread A entered the semaphore.")

        Thread.Sleep(1000)

        Try
            _pool.Release()
            Console.WriteLine("Thread A released the semaphore.")
        Catch ex As Exception
            Console.WriteLine("Thread A: {0}", ex.Message)
        End Try
    End Sub

    Private Shared Sub ThreadB()
        ' Thread B simulates a task that lasts half a second,
        ' then enters the semaphore.
        '
        Thread.Sleep(500)

        _pool.WaitOne()
        Console.WriteLine("Thread B entered the semaphore.")
        
        ' Due to a programming error, Thread B releases the
        ' semaphore twice. To fix the program, delete one line.
        _pool.Release()
        _pool.Release()
        Console.WriteLine("Thread B exits successfully.")
    End Sub
End Class
' This code example produces the following output:
'
' Thread A entered the semaphore.
' Thread B entered the semaphore.
' Thread B exits successfully.
' Thread A: Adding the given count to the semaphore would cause it to exceed its maximum count.
'

import System.*;
import System.Threading.*;

public class Example
{
    // A semaphore that can satisfy at most two concurrent
    // requests.
    //
    private static Semaphore pool = new Semaphore(2, 2);

    public static void main(String[] args)
    {
        // Create and start two threads, A and B. 
        //
        System.Threading.Thread tA = new System.Threading.Thread(new 
            ThreadStart(ThreadA));
        tA.Start();

        System.Threading.Thread tB = new System.Threading.Thread(new 
            ThreadStart(ThreadB));
        tB.Start();
    } //main

    private static void ThreadA()
    {
        // Thread A enters the semaphore and simulates a task
        // that lasts a second.
        //
        pool.WaitOne();
        Console.WriteLine("Thread A entered the semaphore.");
        System.Threading.Thread.Sleep(1000);

        try {
            pool.Release();
            Console.WriteLine("Thread A released the semaphore.");
        }
        catch (System.Exception ex) {
            Console.WriteLine("Thread A: {0}", ex.get_Message());
        }
    } //ThreadA

    private static void ThreadB()
    {
        // Thread B simulates a task that lasts half a second,
        // then enters the semaphore.
        //
        System.Threading.Thread.Sleep(500);
        pool.WaitOne();
        Console.WriteLine("Thread B entered the semaphore.");
        // Due to a programming error, Thread B releases the
        // semaphore twice. To fix the program, delete one line.
        pool.Release();
        pool.Release();
        Console.WriteLine("Thread B exits successfully.");
    } //ThreadB
} //Example
/* This code example produces the following output:

Thread A entered the semaphore.
Thread B entered the semaphore.
Thread B exits successfully.
Thread A: Adding the given count to the semaphore would cause it to 
exceed its maximum count.
 */

System.Object
   System.Exception
     System.SystemException
      System.Threading.SemaphoreFullException

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

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