HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)

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STANDARD Printed by: Nora Chuang [nchuang] STANDARD

/build/1111/BRICK/man2/!!!intro.2

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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 con-

tains 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

Upon success, msem_lock() returns zero; otherwise, it returns −1 and sets errno to indicate the

error.

ERRORS

msem_lock() fails if any of the following conditions are 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.