sem_post(3) [osf1 man page]
sem_post(3) Library Functions Manual sem_post(3) NAME
sem_post - Unlocks a semaphore (P1003.1b) LIBRARY
Realtime Library (librt.so, librt.a) SYNOPSIS
#include <semaphore.h> int sem_post ( sem_t *sem); PARAMETERS
sem Pointer to the semaphore to be unlocked. DESCRIPTION
The sem_post function unlocks the specified semaphore by performing the semaphore unlock operation on that semaphore. The appropriate func- tion (sem_open for named semaphores or sem_init for unnamed semaphores) must be called for a semaphore before you can call the locking and unlocking functions, sem_wait, sem_trywait, and sem_post. If the semaphore value after a sem_post function is positive, no processes were blocked waiting for the semaphore to be unlocked; the sema- phore value is incremented. If the semaphore value after a sem_post function is zero, one of the processes blocked waiting for the sema- phore is allowed to return successfully from its call to sem_wait. If more than one process is blocked while waiting for the semaphore, only one process is unblocked and the state of the semaphore remains unchanged when the sem_post function returns. The process to be unblocked is selected according to the scheduling policies and priorities of all blocked processes. If the scheduling policy is SCHED_FIFO or SCHED_RR, the highest-priority waiting process is unblocked. If more than one process of that priority is blocked, then the process that has waited the longest is unblocked. The sem_post function can be called from a signal-catching function. RETURN VALUES
On successful completion, the sem_post function returns the value 0 (zero) and performs a semaphore unlock operation, unblocking a process. Otherwise, the function returns the value -1 and sets errno to indicate the error. The state of the semaphore remains unchanged. ERRORS
The sem_post function fails under the following condition: [EINVAL] The sem does not refer to a valid semaphore. RELATED INFORMATION
Functions: sem_trywait(3), sem_wait(3) Guide to Realtime Programming delim off sem_post(3)
Check Out this Related Man Page
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)