freebsd-nq/lib/libc/gen/sem_getvalue.3

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.Dd February 15, 2000
.Dt SEM_GETVALUE 3
.Os
.Sh NAME
.Nm sem_getvalue
.Nd get the value of a semaphore
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In semaphore.h
.Ft int
.Fn sem_getvalue "sem_t * restrict sem" "int * restrict sval"
.Sh DESCRIPTION
The
.Fn sem_getvalue
function sets the variable pointed to by
.Fa sval
to the current value of the semaphore pointed to by
.Fa sem ,
as of the time that the call to
.Fn sem_getvalue
is actually run.
.Sh RETURN VALUES
.Rv -std sem_getvalue
.Sh ERRORS
The
.Fn sem_getvalue
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa sem
argument
points to an invalid semaphore.
.El
.Sh SEE ALSO
.Xr sem_post 3 ,
.Xr sem_trywait 3 ,
.Xr sem_wait 3 ,
.Xr sem 4
.Sh STANDARDS
The
.Fn sem_getvalue
function conforms to
.St -p1003.1-96 .
.Pp
The value of the semaphore is never negative, even if there are threads blocked
on the semaphore.
.Tn POSIX
is somewhat ambiguous in its wording with regard to
what the value of the semaphore should be if there are blocked waiting threads,
but this behavior is conformant, given the wording of the specification.