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sem_getvalue(3) — Linux manual page

sem_getvalue(3) Library Functions Manual sem_getvalue(3)

NAME top

 sem_getvalue - get the value of a semaphore

LIBRARY top

 POSIX threads library (libpthread, -lpthread)

SYNOPSIS top

 #include <semaphore.h>
 int sem_getvalue(sem_t *restrict sem, int *restrict sval);

DESCRIPTION top

 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 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 top

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

ERRORS top

 EINVAL sem is not a valid semaphore. (The glibc implementation
 currently does not check whether sem is valid.)

ATTRIBUTES top

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

STANDARDS top

 POSIX.1-2008.

HISTORY top

 POSIX.1-2001.

NOTES top

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

SEE ALSO top

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

COLOPHON top

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 user-space interface documentation) project. Information about
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 This page was obtained from the tarball man-pages-6.10.tar.gz
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Linux man-pages 6.10 2024年07月23日 sem_getvalue(3)

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Pages that refer to this page: sem_close(3), sem_open(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7)

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