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CreateSemaphore

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This function creates a named or unnamed semaphore object.

HANDLE CreateSemaphore(
  LPSECURITY_ATTRIBUTES lpSemaphoreAttributes, 
  LONG lInitialCount, 
  LONG lMaximumCount, 
  LPCTSTR lpName 
);

Parameters

  • lpSemaphoreAttributes
    [in] Set to NULL.

  • lInitialCount
    [in] Specifies an initial count for the semaphore object. This value must be greater than or equal to zero and less than or equal to lMaximumCount. The state of a semaphore is signaled when its count is greater than zero and nonsignaled when it is zero. The count is decreased by one whenever a wait function releases a thread that was waiting for the semaphore. The count is increased by a specified amount by calling the ReleaseSemaphore function.

  • lMaximumCount
    [in] Specifies the maximum count for the semaphore object. This value must be greater than zero.

  • lpName
    [in] Long pointer to a null-terminated string specifying the name of the semaphore object. The name is limited to MAX_PATH characters and can contain any character except the backslash path-separator character (\). Name comparison is case sensitive.

    If lpName matches the name of an existing named semaphore object, the lInitialCount and lMaximumCount parameters are ignored because they have already been set during the creation process.

    If lpName is NULL, the semaphore object is created without a name.

    If lpName semaphore name does not share a name space with events, mutexes, or file-mapping objects.

Return Values

If the function succeeds, the return value is a handle to the semaphore object. If the named semaphore object existed before the function call, the GetLastError function returns ERROR_ALREADY_EXISTS. Otherwise, GetLastError returns zero. If CreateSemaphore fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks

The handle returned by CreateSemaphore can be used in any function that requires a handle to a semaphore object.

Any thread of the calling process can specify the semaphore-object handle in a call to one of the wait functions. The single-object wait functions return when the state of the specified object is signaled. The multiple-object wait functions can be instructed to return either when any one or when all of the specified objects are signaled. When a wait function returns, the waiting thread is released to continue its execution.

The state of a semaphore object is signaled when its count is greater than zero and nonsignaled when its count is equal to zero. The lInitialCount parameter specifies the initial count. Each time a waiting thread is released because of the semaphore's signaled state, the count of the semaphore is decreased by one. Use the ReleaseSemaphore function to increment a semaphore's count by a specified amount. The count can never be less than zero or greater than the value specified in the lMaximumCount parameter.

Multiple processes can have handles of the same semaphore object, enabling use of the object for interprocess synchronization. To share an object, a process can specify the name of a semaphore object in a call to the CreateSemaphore function.

Use the CloseHandle function to close the handle. The system closes the handle automatically when the process terminates. The semaphore object is destroyed when its last handle is closed.

Windows CE does not implement the OpenSemaphore. Use the CreateSemaphore function to open a semaphore.

Requirements

OS Versions: Windows CE 3.0 and later.
Header: Winbase.h.
Link Library: Nk.lib.

See Also

ReleaseSemaphore | CloseHandle

Last updated on Wednesday, April 13, 2005

© 2005 Microsoft Corporation. All rights reserved.