mirror of https://github.com/mkerrisk/man-pages
100 lines
3.6 KiB
Plaintext
100 lines
3.6 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "SEM_INIT" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" sem_init
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.SH NAME
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sem_init \- initialize an unnamed semaphore (\fBREALTIME\fP)
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.SH SYNOPSIS
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.LP
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\fB#include <semaphore.h>
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.br
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.sp
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int sem_init(sem_t *\fP\fIsem\fP\fB, int\fP \fIpshared\fP\fB, unsigned\fP
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\fIvalue\fP\fB); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIsem_init\fP() function shall initialize the unnamed semaphore
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referred to by \fIsem\fP. The value of the initialized
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semaphore shall be \fIvalue\fP. Following a successful call to \fIsem_init\fP(),
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the semaphore may be used in subsequent calls to
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\fIsem_wait\fP(), \fIsem_trywait\fP(), \fIsem_post\fP(), and \fIsem_destroy\fP().
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This
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semaphore shall remain usable until the semaphore is destroyed.
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.LP
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If the \fIpshared\fP argument has a non-zero value, then the semaphore
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is shared between processes; in this case, any process
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that can access the semaphore \fIsem\fP can use \fIsem\fP for performing
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\fIsem_wait\fP(), \fIsem_trywait\fP(), \fIsem_post\fP(), and \fIsem_destroy\fP()
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operations.
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.LP
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Only \fIsem\fP itself may be used for performing synchronization.
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The result of referring to copies of \fIsem\fP in calls to
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\fIsem_wait\fP(), \fIsem_trywait\fP(), \fIsem_post\fP(), and \fIsem_destroy\fP()
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is
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undefined.
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.LP
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If the \fIpshared\fP argument is zero, then the semaphore is shared
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between threads of the process; any thread in this process
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can use \fIsem\fP for performing \fIsem_wait\fP(), \fIsem_trywait\fP(),
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\fIsem_post\fP(), and \fIsem_destroy\fP() operations. The use of the
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semaphore by threads other than those created
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in the same process is undefined.
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.LP
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Attempting to initialize an already initialized semaphore results
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in undefined behavior.
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.SH RETURN VALUE
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.LP
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Upon successful completion, the \fIsem_init\fP() function shall initialize
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the semaphore in \fIsem\fP. Otherwise, it shall
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return -1 and set \fIerrno\fP to indicate the error.
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.SH ERRORS
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.LP
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The \fIsem_init\fP() function shall fail if:
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.TP 7
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.B EINVAL
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The \fIvalue\fP argument exceeds {SEM_VALUE_MAX}.
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.TP 7
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.B ENOSPC
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A resource required to initialize the semaphore has been exhausted,
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or the limit on semaphores ( {SEM_NSEMS_MAX}) has been
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reached.
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.TP 7
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.B EPERM
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The process lacks the appropriate privileges to initialize the semaphore.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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The \fIsem_init\fP() function is part of the Semaphores option and
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need not be available on all implementations.
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.SH RATIONALE
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.LP
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Although this volume of IEEE\ Std\ 1003.1-2001 fails to specify a
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successful return value, it is likely that a later
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version may require the implementation to return a value of zero if
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the call to \fIsem_init\fP() is successful.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIsem_destroy\fP() , \fIsem_post\fP() , \fIsem_timedwait\fP() , \fIsem_trywait\fP()
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, \fIsem_wait\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
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\fI<semaphore.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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