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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DESCRIPTION

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

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

29       EINVAL sem is not a valid semaphore.
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NOTES

32       The value of the  semaphore  may  already  have  changed  by  the  time
33       sem_getvalue() returns.
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CONFORMING TO

36       POSIX.1-2001.
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