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msem_lock.2 (2010 09)

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msem_lock(2) msem_lock(2)
NAME
msem_lock() - lock a semaphore
SYNOPSIS
#include <sys/mman.h>
int msem_lock(
msemaphore *sem,
int condition
);
DESCRIPTION
msem_lock() attempts to lock a binary semaphore.
sem points to an
msemaphore structure which specifies the semaphore to be locked.
If the semaphore is not currently locked, it becomes locked and the function returns successfully.
If the semaphore is currently locked, and condition is
MSEM_IF_NOWAIT, then the function returns with
an error. If the semaphore is currently locked and condition is zero, the function does not return until
either the calling process is able to successfully lock the semaphore, or an error condition occurs.
All calls to
msem_lock() and msem_unlock()
by multiple processes sharing a common msema-
phore structure behave as if the calls were serialized.
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 uniquely identifies the semaphore. If the
msemaphore
structure contains any value copied from an msemaphore structure at a different address, the result is
undefined.
IMPLEMENTATION NOTES
If blocked on a locked semaphore,
msem_lock() suspends the calling process at a priority such that
the process can be interrupted by a signal.
The system attempts to ignore or recover from invalid values written to the
msemaphore structure, but
this is not guaranteed for all cases.
msem_lock() successfully acquires a semaphore that is locked by a process that has exited.
RETURN VALUE
msem_lock() returns one of the following values:
0 Success.
-1 Failure. errno is set to indicate the error.
ERRORS
msem_lock() sets errno to one of the following values if the corresponding condition is encountered.
[EAGAIN]
MSEM_IF_NOWAIT was specified and the semaphore was already locked.
[EINVAL] sem points to an
msemaphore structure that has been removed, or condition is
invalid.
[EINTR]
msem_lock() was interrupted by a signal that was caught.
[EDEADLK] The semaphore is currently locked, condition is zero, and waiting to lock the sema-
phore would create a deadlock.
[EFAULT] sem is not a properly aligned address or is otherwise an invalid pointer.
AUTHOR
msem_lock() was developed by HP and OSF.
SEE ALSO
msem_init(2), msem_remove(2), msem_unlock(2), mman(5).
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

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