sem_getvalue(3)

1SEM_GETVALUE(3)            Linux Programmer's Manual           SEM_GETVALUE(3)
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NAME

6       sem_getvalue - get the value of a semaphore
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SYNOPSIS

9       #include <semaphore.h>
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11       int sem_getvalue(sem_t *sem, int *sval);
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13       Link with -pthread.
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DESCRIPTION

16       sem_getvalue() places the current value of the semaphore pointed to sem
17       into the integer pointed to by sval.
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19       If one or more processes or threads are blocked  waiting  to  lock  the
20       semaphore  with sem_wait(3), POSIX.1-2001 permits two possibilities for
21       the value returned in sval: either 0 is returned; or a negative  number
22       whose  absolute  value  is  the  count  of  the number of processes and
23       threads currently blocked in  sem_wait(3).   Linux  adopts  the  former
24       behavior.
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RETURN VALUE

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

31       EINVAL sem is not a valid semaphore.
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CONFORMING TO

34       POSIX.1-2001.
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NOTES

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

44       This  page  is  part of release 3.53 of the Linux man-pages project.  A
45       description of the project, and information about reporting  bugs,  can
46       be found at http://www.kernel.org/doc/man-pages/.
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50Linux                             2012-05-13                   SEM_GETVALUE(3)