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.\" $FreeBSD: release/9.1.0/lib/libc/gen/sem_init.3 202133 2010-01-12 01:30:05Z davidxu $
.\"
.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
.In 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 .
.Pp
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 .
.Pp
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argument is no longer valid after a successful call to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:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa value
argument exceeds
.Dv SEM_VALUE_MAX .
.It 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 ,
.Xr sem 4
.Sh STANDARDS
The
.Fn sem_init
function conforms to
.St -p1003.1-96 .