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sem_getvalue(S)


sem_getvalue -- get the value of a semaphore

Syntax

cc . . . -lsuds
#include <semaphore.h>

int sem_getvalue (sem_t *sem, int *sval):

Description

The sem_getvalue function updates the location referenced by the sval argument to have the value of the semaphore referenced by sem without affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred at some unspecified time during the call, but may not be the actual value of the semaphore when returned to the calling process.

If sem is locked, the value returned by sem_getvalue is either zero or a negative number. In the latter case, the absolute value represents the number of processes waiting for the semaphore at some unspecified time during the call.

Return values

Upon successful completion, the function returns a value of zero. Otherwise, the function returns a value of -l and sets errno to indicate the error.

Diagnostics

If the following condition occurs, the sem_getvalue function returns -1 and sets errno to the corresponding value:

[EINVAL]
The sem argument does not refer to a valid semaphore.

See also

semaphore(FP), sem_post(S), sem_trywait(S), sem_wait(S)

Standards conformance

Text reprinted and/or adapted from IEEE Std 1003.1b-1993, IEEE Standard for Information Technology, POSIX Part 1: System Application Program Interface (API) Amendment 1: Realtime Extensions [C Language], copyright © 1993 by the Institute of Electrical and Electronics Engineers, Inc. The IEEE takes no responsibility for and will assume no liability for damages resulting from the reader's misinterpretation of said information resulting from the placement and context in this publication. Information is reproduced with the permission of the IEEE.
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