ReleaseSemaphore

A version of this page is also available for

Windows Embedded CE 6.0 R3

4/8/2010

This function increases the count of the specified semaphore object by a specified amount.

Syntax

BOOL ReleaseSemaphore(
  HANDLE hSemaphore,
  LONG lReleaseCount,
  LPLONG lpPreviousCount
);

Parameters

• hSemaphore
  [in] Handle to the semaphore object. The CreateSemaphore function returns this handle.

• lReleaseCount
  [in] Specifies the amount by which the current count of the semaphore object is to be increased. The value must be greater than zero. If the specified amount would cause the count of the semaphore to exceed the maximum count that was specified when the semaphore was created, the count is not changed and the function returns FALSE.

• lpPreviousCount
  [out] Long pointer to a 32-bit variable to receive the previous count for the semaphore. This parameter can be NULL if the previous count is not required.

Return Value

Nonzero indicates success. Zero indicates failure. To get extended error information, call GetLastError.

Remarks

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 process that calls the CreateSemaphore function specifies the semaphore's 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.

Typically, an application uses a semaphore to limit the number of threads using a resource. Before a thread uses the resource, it specifies the semaphore handle in a call to one of the wait functions. When the wait function returns, it decreases the semaphore's count by one. When the thread has finished using the resource, it calls ReleaseSemaphore to increase the semaphore's count by one.

Another use of ReleaseSemaphore is during an application's initialization. The application can create a semaphore with an initial count of zero. This sets the semaphore's state to nonsignaled and blocks all threads from accessing the protected resource. When the application finishes its initialization, it uses ReleaseSemaphore to increase the count to its maximum value to permit normal access to the protected resource.

Each object type, such as memory maps, semaphores, events, message queues, mutexes, and watchdog timers, has its own separate namespace. Empty strings, "", are handled as named objects. On Windows desktop-based platforms, synchronization objects all share the same namespace.

Requirements

See Also

Reference

Synchronization Functions
CreateSemaphore