SemaphoreFullException Class (System.Threading) (original) (raw)

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SemaphoreFullException Class

• Reference

Definition

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

public ref class SemaphoreFullException : Exception

public ref class SemaphoreFullException : SystemException

public class SemaphoreFullException : Exception

public class SemaphoreFullException : SystemException

[System.Runtime.InteropServices.ComVisible(false)]
[System.Serializable]
public class SemaphoreFullException : SystemException

type SemaphoreFullException = class
    inherit Exception

type SemaphoreFullException = class
    inherit SystemException

[<System.Runtime.InteropServices.ComVisible(false)>]
[<System.Serializable>]
type SemaphoreFullException = class
    inherit SystemException

Public Class SemaphoreFullException
Inherits Exception

Public Class SemaphoreFullException
Inherits SystemException

Inheritance

Inheritance

Attributes

Examples

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

public ref class Example
{
private:
   // A semaphore that can satisfy at most two concurrent
   // requests.
   //
   static Semaphore^ _pool = gcnew Semaphore( 2,2 );

public:
   static void main()
   {
      // Create and start two threads, A and B.
      //
      Thread^ tA = gcnew Thread( gcnew ThreadStart( ThreadA ) );
      tA->Start();

      Thread^ tB = gcnew Thread( gcnew 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( L"Thread A entered the semaphore." );

      Thread::Sleep( 1000 );

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

   static void ThreadB()
   {
      // Thread B simulates a task that lasts half a second,
      // then enters the semaphore.
      //
      Thread::Sleep( 500 );

      _pool->WaitOne();
      Console::WriteLine( L"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( L"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.
 */

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.
 */

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.
'

Remarks

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 Semaphore.Release method at this point, a SemaphoreFullException is thrown.

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.

Constructors

Properties

Methods

Events

Applies to

See also

• Semaphore
• Semaphore

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