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.Dd January 9, 2010 .Dt SEM_INIT 3 .Os .Sh NAME .Nm sem_init .Nd initialize an unnamed semaphore .Sh LIBRARY .Lb libc .Sh SYNOPSIS n semaphore.h .Ft int .Fn sem_init "sem_t *sem" "int pshared" "unsigned int value" .Sh DESCRIPTION The .Fn sem_init function initializes the unnamed semaphore pointed to by .Fa sem to have the value .Fa value .
p A non-zero value for .Fa pshared specifies a shared semaphore that can be used by multiple processes, the semaphore should be located in shared memory region (see .Xr mmap 2 , .Xr shm_open 2 , and .Xr shmget 2 ) , any process having read and write access to address .Fa sem can perform semaphore operations on .Fa sem .
p Following a successful call to .Fn sem_init , .Fa sem can be used as an argument in subsequent calls to .Xr sem_wait 3 , .Xr sem_trywait 3 , .Xr sem_post 3 , and .Xr sem_destroy 3 . The .Fa sem argument is no longer valid after a successful call to .Xr sem_destroy 3 . .Sh RETURN VALUES .Rv -std sem_init .Sh ERRORS The .Fn sem_init function will fail if: l -tag -width Er t Bq Er EINVAL The .Fa value argument exceeds .Dv SEM_VALUE_MAX . t Bq Er ENOSPC Memory allocation error. .El .Sh SEE ALSO .Xr sem_destroy 3 , .Xr sem_getvalue 3 , .Xr sem_post 3 , .Xr sem_trywait 3 , .Xr sem_wait 3 .Sh STANDARDS The .Fn sem_init function conforms to .St -p1003.1-96 .