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Dd February 29, 2012
Dt SEM_GETVALUE 3
Os
Sh NAME
Nm sem_getvalue
Nd get the value of a semaphore
Sh LIBRARY
Lb librt
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
Fn sem_getvalue
will fail if:
Bl -tag -width Er
It Bq Er EINVAL
Fa sem
points to an invalid semaphore.
El
Sh SEE ALSO
Xr sem_post 3 ,
Xr sem_timedwait 3 ,
Xr sem_trywait 3 ,
Xr sem_wait 3
Sh STANDARDS
Fn sem_getvalue
conforms to
St -p1003.1-96 .
Pp
The value of the semaphore is never negative, even if there are threads blocked
on the semaphore.
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.
