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SemaphoreFullException Class

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


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

public class SemaphoreFullException : SystemException

The SemaphoreFullException type exposes the following members.

Public methodSemaphoreFullException()Initializes a new instance of the SemaphoreFullException class with default values.
Public methodSemaphoreFullException(String)Initializes a new instance of the SemaphoreFullException class with a specified error message.
Protected methodSemaphoreFullException(SerializationInfo, StreamingContext)Initializes a new instance of the SemaphoreFullException class with serialized data.
Public methodSemaphoreFullException(String, Exception)Initializes a new instance of the SemaphoreFullException class with a specified error message and a reference to the inner exception that is the cause of this exception.

Public propertyDataGets a collection of key/value pairs that provide additional user-defined information about the exception. (Inherited from Exception.)
Public propertyHelpLinkGets or sets a link to the help file associated with this exception. (Inherited from Exception.)
Protected propertyHResultGets or sets HRESULT, a coded numerical value that is assigned to a specific exception. (Inherited from Exception.)
Public propertyInnerExceptionGets the Exception instance that caused the current exception. (Inherited from Exception.)
Public propertyMessageGets a message that describes the current exception. (Inherited from Exception.)
Public propertySourceGets or sets the name of the application or the object that causes the error. (Inherited from Exception.)
Public propertyStackTraceGets a string representation of the immediate frames on the call stack. (Inherited from Exception.)
Public propertyTargetSiteGets the method that throws the current exception. (Inherited from Exception.)

Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetBaseExceptionWhen overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. (Inherited from Exception.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetObjectDataWhen overridden in a derived class, sets the SerializationInfo with information about the exception. (Inherited from Exception.)
Public methodGetTypeGets the runtime type of the current instance. (Inherited from Exception.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringCreates and returns a string representation of the current exception. (Inherited from Exception.)

Protected eventSerializeObjectStateOccurs when an exception is serialized to create an exception state object that contains serialized data about the exception. (Inherited from Exception.)

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.


The Semaphore class does not enforce thread identity on calls to the WaitHandle.WaitOne and 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));

        Thread tB = new Thread(new ThreadStart(ThreadB));

    private static void ThreadA()
        // Thread A enters the semaphore and simulates a task
        // that lasts a second.
        Console.WriteLine("Thread A entered the semaphore.");


            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.

        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.
        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.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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