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 permits two possibilities for the
21       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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ATTRIBUTES

34       For  an  explanation  of  the  terms  used   in   this   section,   see
35       attributes(7).
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37       ┌───────────────┬───────────────┬─────────┐
38       │Interface      │ Attribute     │ Value   │
39       ├───────────────┼───────────────┼─────────┤
40       │sem_getvalue() │ Thread safety │ MT-Safe │
41       └───────────────┴───────────────┴─────────┘

CONFORMING TO

43       POSIX.1-2001, POSIX.1-2008.
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NOTES

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

53       This page is part of release 4.16 of the Linux  man-pages  project.   A
54       description  of  the project, information about reporting bugs, and the
55       latest    version    of    this    page,    can     be     found     at
56       https://www.kernel.org/doc/man-pages/.
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60Linux                             2017-09-15                   SEM_GETVALUE(3)