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107 lines
3.5 KiB
Plaintext
107 lines
3.5 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "SEM_TRYWAIT" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" sem_trywait
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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.SH NAME
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sem_trywait, sem_wait \- lock a 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_trywait(sem_t *\fP\fIsem\fP\fB);
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.br
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int sem_wait(sem_t *\fP\fIsem\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_trywait\fP() function shall lock the semaphore referenced
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by \fIsem\fP only if the semaphore is currently not
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locked; that is, if the semaphore value is currently positive. Otherwise,
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it shall not lock the semaphore.
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.LP
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The \fIsem_wait\fP() function shall lock the semaphore referenced
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by \fIsem\fP by performing a semaphore lock operation on
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that semaphore. If the semaphore value is currently zero, then the
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calling thread shall not return from the call to
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\fIsem_wait\fP() until it either locks the semaphore or the call is
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interrupted by a signal.
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.LP
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Upon successful return, the state of the semaphore shall be locked
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and shall remain locked until the \fIsem_post\fP() function is executed
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and returns successfully.
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.LP
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The \fIsem_wait\fP() function is interruptible by the delivery of
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a signal.
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.SH RETURN VALUE
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.LP
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The \fIsem_trywait\fP() and \fIsem_wait\fP() functions shall return
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zero if the calling process successfully performed the
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semaphore lock operation on the semaphore designated by \fIsem\fP.
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If the call was unsuccessful, the state of the semaphore shall
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be unchanged, and the function shall return a value of -1 and set
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\fIerrno\fP to indicate the error.
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.SH ERRORS
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.LP
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The \fIsem_trywait\fP() and \fIsem_wait\fP() functions shall fail
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if:
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.TP 7
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.B EAGAIN
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The semaphore was already locked, so it cannot be immediately locked
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by the \fIsem_trywait\fP() operation (
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\fIsem_trywait\fP() only).
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.TP 7
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.B EINVAL
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The \fIsem\fP argument does not refer to a valid semaphore.
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.sp
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.LP
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The \fIsem_trywait\fP() and \fIsem_wait\fP() functions may fail if:
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.TP 7
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.B EDEADLK
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A deadlock condition was detected.
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.TP 7
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.B EINTR
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A signal interrupted this function.
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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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Applications using these functions may be subject to priority inversion,
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as discussed in the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, Section 3.285, Priority Inversion.
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.LP
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The \fIsem_trywait\fP() and \fIsem_wait\fP() functions are part of
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the Semaphores option and need not be provided on all
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implementations.
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.SH RATIONALE
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.LP
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None.
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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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\fIsemctl\fP(), \fIsemget\fP(), \fIsemop\fP(),
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\fIsem_post\fP(), \fIsem_timedwait\fP(), the Base Definitions
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volume of IEEE\ Std\ 1003.1-2001, \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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