2006-03-25 20:42:27 +00:00
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'\" t
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
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.TH SEM_GETVALUE 3 2006-03-25 "Linux 2.6.16" "Linux Programmer's Manual"
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.SH NAME
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sem_getvalue \- get the value of 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_getvalue(sem_t *" sem ", int *" sval );
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.fi
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.SH DESCRIPTION
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.BR sem_getvalue ()
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places the current value of the semaphore pointed to
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.I sem
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into the integer pointed to by
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.IR sval .
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If one or more processes or threads are blocked
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waiting to lock the semaphore with
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.BR sem_wait (3),
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POSIX.1-2001 permits two possibilities for the value returned in
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2006-08-03 02:25:12 +00:00
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.IR sval :
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2006-03-25 20:42:27 +00:00
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either 0 is returned;
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or a negative number whose absolute value is the count
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of the number of processes and threads currently blocked in
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.BR sem_wait (3).
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Linux adopts the former behaviour.
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.SH RETURN VALUE
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.BR sem_getvalue ()
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returns 0 on success;
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on error, \-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 NOTES
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The value of the semaphore may already have changed by the time
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.BR sem_getvalue ()
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returns.
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR sem_post (3),
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.BR sem_wait (3),
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.BR sem_overview (7)
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