freebsd-dev/lib/libc_r/man/sem_init.3

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.Dd February 15, 2000
.Dt SEM_INIT 3
.Os
.Sh NAME
.Nm sem_init
.Nd initialize an unnamed semaphore
.Sh LIBRARY
.Lb libc_r
.Sh SYNOPSIS
.Fd #include <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 .
A non-zero value for
.Fa pshared
specifies a shared semaphore that can be used by multiple processes, which this
implementation is not capable of.
.Pp
Following a successful call to
.Fn sem_init ,
.Fa sem
can be used as an argument in subsequent calls to
.Fa sem_wait ,
.Fa sem_trywait ,
.Fa sem_post ,
and
.Fa sem_destroy .
.Fa sem
is no longer valid after a successful call to
.Fa sem_destroy .
.Sh RETURN VALUES
If successful,
.Fn sem_init
returns 0.  Otherwise, -1 is returned and
.Va errno
is set to indicate the type of
error.
.Sh ERRORS
.Fn sem_init
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa value
exceeds SEM_VALUE_MAX.
.It Bq Er ENOSPC
Memory allocation error.
.It Bq Er EPERM
Unable to initialize a shared semaphore.
.El
.Sh SEE ALSO
.Xr sem_destroy 3 ,
.Xr sem_post 3 ,
.Xr sem_trywait 3 ,
.Xr sem_wait 3
.Sh STANDARDS
.Fn sem_init
conforms to
.St -p1003.1-96 .
.Pp
This implementation does not support shared semaphores, and reports this fact
by setting
.Va errno
to
.Er EPERM .
This is perhaps a stretch of the intention of POSIX, but is
compliant, with the caveat that
.Fn sem_init
always reports a permissions error when an attempt to create a shared semaphore
is made.