trusty (3) sem_getvalue.3.gz

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NAME
       sem_getvalue - get the value of a semaphore


SYNOPSIS
       #include <semaphore.h>

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

       Link with -pthread.


DESCRIPTION
       sem_getvalue()  places  the  current value of the semaphore pointed to sem into the integer pointed to by
       sval.

       If one or more processes or  threads  are  blocked  waiting  to  lock  the  semaphore  with  sem_wait(3),
       POSIX.1-2001  permits  two  possibilities  for  the  value  returned  in sval: either 0 is returned; or a
       negative number whose absolute value is the count of  the  number  of  processes  and  threads  currently
       blocked in sem_wait(3).  Linux adopts the former behavior.


RETURN VALUE
       sem_getvalue() returns 0 on success; on error, -1 is returned and errno is set to indicate the error.


ERRORS
       EINVAL sem is not a valid semaphore.


CONFORMING TO
       POSIX.1-2001.


NOTES
       The value of the semaphore may already have changed by the time sem_getvalue() returns.


SEE ALSO
       sem_post(3), sem_wait(3), sem_overview(7)


COLOPHON
       This  page  is  part  of  release 3.54 of the Linux man-pages project.  A description of the project, and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.