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sem_getvalue(3)
NAME
  sem_getvalue - Gets the value of a specified semaphore (P1003.1b)

SYNOPSIS
  #include <semaphore.h>

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

LIBRARY
  Realtime Library (librt.so, librt.a)

PARAMETERS
  sem Specifies a pointer to the semaphore for which a value is to be
      returned.

  sval
      References a location to be updated with the value of the semaphore
      indicated by the sem argument.

DESCRIPTION
  The sem_getvalue function updates a location referenced by the sval
  argument with the value of semaphore sem.  The updated value represents an
  actual semaphore value that occurred during the call, but may not be the
  actual value of the semaphore at the time that the value is returned to the
  calling process.

  If the semaphore is locked, the value returned will either be zero or a
  negative number indicating the number of processes waiting for the
  semaphore at some time during the call.

RETURN VALUES
  On a successful call, a value of 0 (zero) is returned. Otherwise, a value
  of -1 is returned and errno is set to indicate that an error occurred.

ERRORS
  The  sem_getvalue function fails under the following condition:

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

SEE ALSO
  Functions: sem_post(3), sem_trywait(3), sem_wait(3)

  Guide to Realtime Programming

Index for Section 3

Alphabetical listing for S

Top of page