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Man Pages
SEM_INIT(3) FreeBSD Library Functions Manual SEM_INIT(3)

sem_init
initialize an unnamed semaphore

Standard C Library (libc, -lc)

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

The sem_init() function initializes the unnamed semaphore pointed to by sem to have the value value.
A non-zero value for pshared specifies a shared semaphore that can be used by multiple processes, the semaphore should be located in shared memory region (see mmap(2), shm_open(2), and shmget(2)), any process having read and write access to address sem can perform semaphore operations on sem.
Following a successful call to sem_init(), sem can be used as an argument in subsequent calls to sem_wait(3), sem_trywait(3), sem_post(3), and sem_destroy(3). The sem argument is no longer valid after a successful call to sem_destroy(3).

The sem_init() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The sem_init() function will fail if:
[]
The value argument exceeds SEM_VALUE_MAX.
[]
Memory allocation error.

sem_destroy(3), sem_getvalue(3), sem_post(3), sem_trywait(3), sem_wait(3)

The sem_init() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).
January 9, 2010 FreeBSD 12.0-RELEASE

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