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)
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sem_init(3RT) Realtime Library Functions sem_init(3RT) NAME
sem_init - initialize an unnamed semaphore SYNOPSIS
cc [ flag... ] file... -lrt [ library... ] #include <semaphore.h> int sem_init(sem_t *sem, int pshared, unsigned int value); DESCRIPTION
The sem_init() function is used to initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore is value. Following a successful call to sem_init(), the semaphore may be used in subsequent calls to sem_wait(3RT), sem_trywait(3RT), sem_post(3RT), and sem_destroy(3RT). This semaphore remains usable until the semaphore is destroyed. If the pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process that can access the semaphore sem can use sem for performing sem_wait(3RT), sem_trywait(3RT), sem_post(3RT), and sem_destroy(3RT) operations. Only sem itself may be used for performing synchronization. The result of referring to copies of sem in calls to sem_wait(3RT), sem_try- wait(3RT), sem_post(3RT), and sem_destroy(3RT), is undefined. If the pshared argument is zero, then the semaphore is shared between threads of the process; any thread in this process can use sem for performing sem_wait(3RT), sem_trywait(3RT), sem_post(3RT), and sem_destroy(3RT) operations. The use of the semaphore by threads other than those created in the same process is undefined. Attempting to initialize an already initialized semaphore results in undefined behavior. RETURN VALUES
Upon successful completion, the function initializes the semaphore in sem. Otherwise, it returns -1 and sets errno to indicate the error. ERRORS
The sem_init() function will fail if: EINVAL The value argument exceeds SEM_VALUE_MAX. ENOSPC A resource required to initialize the semaphore has been exhausted, or the resources have reached the limit on semaphores (SEM_NSEMS_MAX). ENOSYS The sem_init() function is not supported by the system. EPERM The process lacks the appropriate privileges to initialize the semaphore. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
sem_destroy(3RT), sem_post(3RT), sem_wait(3RT), attributes(5), standards(5) SunOS 5.10 28 Jun 2002 sem_init(3RT)