Information
The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

SemaphoreFullException Class

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)

[SerializableAttribute] 
[ComVisibleAttribute(false)] 
public class SemaphoreFullException : SystemException
/** @attribute SerializableAttribute() */ 
/** @attribute ComVisibleAttribute(false) */ 
public class SemaphoreFullException extends SystemException
SerializableAttribute 
ComVisibleAttribute(false) 
public class SemaphoreFullException extends SystemException
Not applicable.

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.

using System;
using 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()
    {
        // Create and start two threads, A and B. 
        //
        Thread tA = new Thread(new ThreadStart(ThreadA));
        tA.Start();

        Thread tB = new Thread(new ThreadStart(ThreadB));
        tB.Start();
    }

    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.");

        Thread.Sleep(1000);

        try
        {
            _pool.Release();
            Console.WriteLine("Thread A released the semaphore.");
        }
        catch(Exception ex)
        {
            Console.WriteLine("Thread A: {0}", ex.Message);
        }
    }

    private static void 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.");
    }
}
/* 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 Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

Community Additions

Show:
© 2014 Microsoft