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Overview |
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Group |
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Quick Info
Windows NT
| Yes
| Win95
| Yes
| Win32s
| No
| Import Library
| kernel32.lib
| Header File
| winbase.h
| Unicode
| No
| Platform Notes
| None
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ReleaseSemaphore
The ReleaseSemaphore function increases the count of the specified semaphore object by a specified
amount.
BOOL ReleaseSemaphore(
HANDLE hSemaphore,
| // handle of the semaphore object
| LONG lReleaseCount,
| // amount to add to current count
| LPLONG lpPreviousCount
| // address of previous count
| );
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Parameters
hSemaphore
Identifies the semaphore object. The CreateSemaphore or OpenSemaphore function returns this handle.
Windows NT: This handle must have SEMAPHORE_MODIFY_STATE access. For more information,
see Interprocess Synchronization Objects.
lReleaseCount
Specifies the amount by which the semaphore object's current count is to be
increased. The value must be greater than zero. If the specified amount would
cause the semaphore's count to exceed the maximum count that was specified when
the semaphore was created, the count is not changed and the function returns
FALSE.
lpPreviousCount
Points 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 Values
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. 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.
See Also
CreateSemaphore, OpenSemaphore
Related Links
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Unix Manual Pages
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