mirror of https://github.com/mkerrisk/man-pages
70 lines
2.1 KiB
Groff
70 lines
2.1 KiB
Groff
'\" t
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.TH SEM_POST 3 2008-05-29 "Linux" "Linux Programmer's Manual"
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.SH NAME
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sem_post \- unlock a semaphore
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.SH SYNOPSIS
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.nf
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.B #include <semaphore.h>
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.sp
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.BI "int sem_post(sem_t *" sem );
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.fi
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.sp
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Link with \fI\-lrt\fP or \fI\-pthread\fP.
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.SH DESCRIPTION
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.BR sem_post ()
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increments (unlocks) the semaphore pointed to by
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.IR sem .
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If the semaphore's value consequently becomes greater than zero,
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then another process or thread blocked in a
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.BR sem_wait (3)
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call will be woken up and proceed to lock the semaphore.
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.SH RETURN VALUE
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.BR sem_post ()
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returns 0 on success;
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on error, the value of the semaphore is left unchanged,
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\-1 is returned, and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EINVAL
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.I sem
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is not a valid semaphore.
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH NOTES
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.BR sem_post ()
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is async-signal-safe:
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it may be safely called within a signal handler.
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.SH EXAMPLE
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See
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.BR sem_wait (3).
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.SH "SEE ALSO"
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.BR sem_getvalue (3),
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.BR sem_wait (3),
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.BR sem_overview (7)
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