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sem_post(3c) [opensolaris man page]

sem_post(3C)						   Standard C Library Functions 					      sem_post(3C)

NAME
sem_post - increment the count of a semaphore SYNOPSIS
#include <semaphore.h> int sem_post(sem_t *sem); DESCRIPTION
The sem_post() function unlocks the semaphore referenced by sem by performing a semaphore unlock operation on that semaphore. If the semaphore value resulting from this operation is positive, then no threads were blocked waiting for the semaphore to become unlocked; the semaphore value is simply incremented. If the value of the semaphore resulting from this operation is 0, then one of the threads blocked waiting for the semaphore will be allowed to return successfully from its call to sem_wait(3C). If the symbol _POSIX_PRIORITY_SCHEDULING is defined, the thread to be unblocked will be chosen in a manner appropriate to the scheduling policies and parameters in effect for the blocked threads. In the case of the schedulers SCHED_FIFO and SCHED_RR, the highest priority waiting thread will be unblocked, and if there is more than one highest priority thread blocked waiting for the semaphore, then the highest priority thread that has been waiting the longest will be unblocked. If the symbol _POSIX_PRIORITY_SCHEDULING is not defined, the choice of a thread to unblock is unspecified. RETURN VALUES
If successful, sem_post() returns 0; otherwise it returns -1 and sets errno to indicate the error. ERRORS
The sem_post() function will fail if: EINVAL The sem argument does not refer to a valid semaphore. ENOSYS The sem_post() function is not supported by the system. EOVERFLOW The semaphore value exceeds SEM_VALUE_MAX. USAGE
The sem_post() function is reentrant with respect to signals and may be invoked from a signal-catching function. The semaphore functional- ity described on this manual page is for the POSIX (see standards(5)) threads implementation. For the documentation of the Solaris threads interface, see semaphore(3C)). EXAMPLES
See sem_wait(3C). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ |Standard |See standards(5). | +-----------------------------+-----------------------------+ SEE ALSO
sched_setscheduler(3C), sem_wait(3C), semaphore(3C), attributes(5), standards(5) SunOS 5.11 5 Feb 2008 sem_post(3C)

Check Out this Related Man Page

sem_wait(3)						     Library Functions Manual						       sem_wait(3)

NAME
sem_wait, sem_trywait - Performs (or conditionally performs) a semaphore lock (P1003.1b) LIBRARY
Realtime Library (librt.so, librt.a) SYNOPSIS
#include <semaphore.h> int sem_wait ( sem_t *sem); int sem_trywait ( sem_t *sem); PARAMETERS
sem Specifies a pointer to the semaphore to be locked. DESCRIPTION
The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero, the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal. The sem_trywait function locks a semaphore only if the semaphore is currently not locked. If the semaphore value is zero, the sem_trywait function returns without locking the semaphore. These functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains locked until the process unlocks it with a call to the sem_post function. Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore. RETURN VALUES
If the sem_wait or sem_trywait function returns successfully, a value of 0 (zero) is returned and the function executes the semaphore lock operation. On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains unchanged. ERRORS
The sem_wait and sem_trywait functions fail under the following conditions: [EAGAIN] The semaphore was already locked and cannot be locked by the sem_trywait operation (sem_trywait only). [EINTR] A signal interrupted this function. [EINVAL] The sem argument does not refer to a valid semaphore. RELATED INFORMATION
Functions: sem_post(3) Guide to Realtime Programming delim off sem_wait(3)
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