sem_init

sem_init - initialize an unnamed semaphore

#include <semaphore.h>
 I int sem_init(sem_t * sem , int  pshared , unsigned int  value );

R sem_init () initializes the unnamed semaphore at the address pointed to by R sem . The value argument specifies the initial value for the semaphore. The pshared argument indicates whether this semaphore is to be shared between the threads of a process, or between processes. If pshared has the value 0, then the semaphore is shared between the threads of a process, and should be located at some address that is visible to all threads (e.g., a global variable, or a variable allocated dynamically on the heap). If pshared is non-zero, then the semaphore is shared between processes, and should be located in a region of shared memory (see shm_open(3), mmap(2), and shmget(2)). (Since a child created by fork(2) inherits its parent's memory mappings, it can also access the semaphore.) Any process that can access the shared memory region can operate on the semaphore using sem_post(3), sem_wait(3), etc. Initializing a semaphore that has already been initialized results in undefined behavior.

R sem_init () returns 0 on success; on error, -1 is returned, and errno is set to indicate the error.

EINVAL

ENOSYS

POSIX.1-2001.

Bizarrely, POSIX.1-2001 does not specify the value that should be returned by a successful call to R sem_init (). However, virtually every implementation returns zero in this case.

sem_destroy(3), sem_post(3), sem_wait(3), sem_overview(7)