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 *restrict sem, int *restrict 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  be‐
24       havior.
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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.  (The  glibc  implementation  cur‐
32              rently does not check whether sem is valid.)
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ATTRIBUTES

35       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
36       tributes(7).
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38       ┌────────────────────────────────────────────┬───────────────┬─────────┐
39       │Interface                                   │ Attribute     │ Value   │
40       ├────────────────────────────────────────────┼───────────────┼─────────┤
41       │sem_getvalue()                              │ Thread safety │ MT-Safe │
42       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

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

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

55       This  page  is  part of release 5.12 of the Linux man-pages project.  A
56       description of the project, information about reporting bugs,  and  the
57       latest     version     of     this    page,    can    be    found    at
58       https://www.kernel.org/doc/man-pages/.
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62Linux                             2021-03-22                   SEM_GETVALUE(3)