msem_lock(3)msem_lock(3)NAMEmsem_lock - Lock a semaphore
SYNOPSIS
#include <sys/mman.h>
int msem_lock(
msemaphore *sem,
int condition );
LIBRARY
Standard C Library (libc)
PARAMETERS
Points to an msemaphore structure which specifies the semaphore to be
locked. Determines whether the msem_lock() function waits for a cur‐
rently locked semaphore to unlock.
DESCRIPTION
The msem_lock() function attempts to lock a binary semaphore.
If the semaphore is not currently locked, it is locked and the
msem_lock() function returns successfully.
If the semaphore is currently locked, and the condition parameter is
MSEM_IF_NOWAIT, then the msem_lock() function returns with an error. If
the semaphore is currently locked, and the condition parameter is 0
(zero), then msem_lock() will not return until either the calling
process is able to successfully lock the semaphore, or an error condi‐
tion occurs.
All calls to msem_lock() and msem_unlock() by multiple processes shar‐
ing a common msemaphore structure behave as if the calls were serial‐
ized.
If the msemaphore structure contains any value not resulting from a
call to msem_init() followed by a (possibly empty) sequence of calls to
msem_lock() and msem_unlock(), the results are undefined. The address
of an msemaphore structure may be significant. If the msemaphore struc‐
ture contains any value copied from an msemaphore structure at a dif‐
ferent address, the result is undefined.
NOTES
Trial use
RETURN VALUES
On successful completion, the msem_lock() function returns 0 (zero). On
error, the msem_lock() function returns -1 and sets errno to indicate
the error.
ERRORS
If the msem_lock() function fails, errno may be set to one of the fol‐
lowing values: MSEM_IF_NOWAIT was specified and the semaphore was
already locked. The sem parameter points to an msemaphore structure
which specifies a semaphore which has been removed, or the condition
parameter is invalid. The msem_lock() function was interrupted by a
signal which was caught.
SEE ALSO
Functions: msem_init(3), msem_remove(3), msem_unlock(3)msem_lock(3)