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| author | rpj <rpj> | 2005-05-05 14:18:27 +0000 |
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| committer | rpj <rpj> | 2005-05-05 14:18:27 +0000 |
| commit | 41f88a82b33cdb357c83b582381232733ed2d039 (patch) | |
| tree | b3690e999b4d934fce7aab79b2693ab086a4ad46 /manual/pthread_mutex_init.html | |
| parent | b75686484d99c90317b64184ce5080093ee7d2a9 (diff) | |
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diff --git a/manual/pthread_mutex_init.html b/manual/pthread_mutex_init.html new file mode 100644 index 0000000..a56f77d --- /dev/null +++ b/manual/pthread_mutex_init.html @@ -0,0 +1,275 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<HTML> +<HEAD> + <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8"> + <TITLE>PTHREAD_MUTEX(3) manual page</TITLE> + <META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)"> + <META NAME="CREATED" CONTENT="20050505;5000"> + <META NAME="CHANGED" CONTENT="20050505;19000600"> + <!-- manual page source format generated by PolyglotMan v3.2, --> + <!-- available at http://polyglotman.sourceforge.net/ --> +</HEAD> +<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR"> +<P><A HREF="#toc">Table of Contents</A></P> +<H2><A HREF="#toc0" NAME="sect0">Name</A></H2> +<P>pthread_mutex_init, pthread_mutex_lock, pthread_mutex_trylock, +pthread_mutex_timedlock, pthread_mutex_unlock, pthread_mutex_destroy +- operations on mutexes +</P> +<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2> +<P><B>#include <pthread.h></B> +</P> +<P><B>#include <time.h></B></P> +<P><B>pthread_mutex_t </B><I>fastmutex</I> <B>= +PTHREAD_MUTEX_INITIALIZER;</B> +</P> +<P><B>pthread_mutex_t </B><I>recmutex</I> <B>= +PTHREAD_RECURSIVE_MUTEX_INITIALIZER;</B> +</P> +<P><B>pthread_mutex_t </B><I>errchkmutex</I> <B>= +PTHREAD_ERRORCHECK_MUTEX_INITIALIZER;</B> +</P> +<P><B>pthread_mutex_t </B><I>recmutex</I> <B>= +PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;</B> +</P> +<P><B>pthread_mutex_t </B><I>errchkmutex</I> <B>= +PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;</B> +</P> +<P><B>int pthread_mutex_init(pthread_mutex_t *</B><I>mutex</I><B>, +const pthread_mutexattr_t *</B><I>mutexattr</I><B>);</B> +</P> +<P><B>int pthread_mutex_lock(pthread_mutex_t *</B><I>mutex</I><B>);</B> +</P> +<P><B>int pthread_mutex_trylock(pthread_mutex_t *</B><I>mutex</I><B>);</B> +</P> +<P><B>int pthread_mutex_timedlock(pthread_mutex_t *</B><I>mutex, +</I><B>const struct timespec *</B><I>abs_timeout</I><B>);</B> +</P> +<P><B>int pthread_mutex_unlock(pthread_mutex_t *</B><I>mutex</I><B>);</B> +</P> +<P><B>int pthread_mutex_destroy(pthread_mutex_t *</B><I>mutex</I><B>);</B> +</P> +<H2><A HREF="#toc2" NAME="sect2">Description</A></H2> +<P>A mutex is a MUTual EXclusion device, and is useful for protecting +shared data structures from concurrent modifications, and +implementing critical sections and monitors. +</P> +<P>A mutex has two possible states: unlocked (not owned by any +thread), and locked (owned by one thread). A mutex can never be owned +by two different threads simultaneously. A thread attempting to lock +a mutex that is already locked by another thread is suspended until +the owning thread unlocks the mutex first. +</P> +<P><B>pthread_mutex_init</B> initializes the mutex object pointed to +by <I>mutex</I> according to the mutex attributes specified in +<I>mutexattr</I>. If <I>mutexattr</I> is <B>NULL</B>, default +attributes are used instead. +</P> +<P>The type of a mutex determines whether it can be locked again by a +thread that already owns it. The default type is “normal”. See +<A HREF="pthread_mutexattr_init.html"><B>pthread_mutexattr_init</B>(3)</A> +for more information on mutex attributes. +</P> +<P>Variables of type <B>pthread_mutex_t</B> can also be initialized +statically, using the constants <B>PTHREAD_MUTEX_INITIALIZER</B> (for +normal “fast” mutexes), <B>PTHREAD_RECURSIVE_MUTEX_INITIALIZER</B> +(for recursive mutexes), and <B>PTHREAD_ERRORCHECK_MUTEX_INITIALIZER</B> +(for error checking mutexes). <SPAN STYLE="font-weight: medium"> In +the <B>Pthreads-w32</B> implementation, an application should still +call <B>pthread_mutex_destroy</B> at some point to ensure that any +resources consumed by the mutex are released.</SPAN></P> +<P><B>pthread_mutex_lock</B> locks the given mutex. If the mutex is +currently unlocked, it becomes locked and owned by the calling +thread, and <B>pthread_mutex_lock</B> returns immediately. If the +mutex is already locked by another thread, <B>pthread_mutex_lock</B> +suspends the calling thread until the mutex is unlocked. +</P> +<P>If the mutex is already locked by the calling thread, the behavior +of <B>pthread_mutex_lock</B> depends on the type of the mutex. If the +mutex is of the “normal” type, the calling thread is suspended +until the mutex is unlocked, thus effectively causing the calling +thread to deadlock. If the mutex is of the ‘‘error checking’’ +type, <B>pthread_mutex_lock</B> returns immediately with the error +code <B>EDEADLK</B>. If the mutex is of the ‘‘recursive’’ +type, <B>pthread_mutex_lock</B> succeeds and returns immediately, +recording the number of times the calling thread has locked the +mutex. An equal number of <B>pthread_mutex_unlock</B> operations must +be performed before the mutex returns to the unlocked state. +</P> +<P><B>pthread_mutex_trylock</B> behaves identically to +<B>pthread_mutex_lock</B>, except that it does not block the calling +thread if the mutex is already locked by another thread (or by the +calling thread in the case of a “normal” mutex). Instead, +<B>pthread_mutex_trylock</B> returns immediately with the error code +<B>EBUSY</B>. +</P> +<P><B>pthread_mutex_timedlock</B> behaves identically to +<B>pthread_mutex_lock</B>, except that if it cannot acquire the lock +before the <I>abs_timeout</I> time, the call returns with the error +code <B>ETIMEDOUT</B>. If the mutex can be locked immediately it is, +and the <B>abs_timeout</B> parameter is ignored.</P> +<P><B>pthread_mutex_unlock</B> unlocks the given mutex. The mutex is +assumed to be locked and owned by the calling thread on entrance to +<B>pthread_mutex_unlock</B>. If the mutex is of the “normal” +type, <B>pthread_mutex_unlock</B> always returns it to the unlocked +state. If it is of the ‘‘recursive’’ type, it decrements the +locking count of the mutex (number of <B>pthread_mutex_lock</B> +operations performed on it by the calling thread), and only when this +count reaches zero is the mutex actually unlocked. +</P> +<P>On ‘‘error checking’’ mutexes, <B>pthread_mutex_unlock</B> +actually checks at run-time that the mutex is locked on entrance, and +that it was locked by the same thread that is now calling +<B>pthread_mutex_unlock</B>. If these conditions are not met, an +error code is returned and the mutex remains unchanged. ‘‘Normal’’ +mutexes perform no such checks, thus allowing a locked mutex to be +unlocked by a thread other than its owner. This is non-portable +behavior and is not meant to be used as a feature.</P> +<P><B>pthread_mutex_destroy</B> destroys a mutex object, freeing the +resources it might hold. The mutex must be unlocked on entrance.</P> +<H2><A HREF="#toc3" NAME="sect3">Cancellation</A></H2> +<P>None of the mutex functions is a cancellation point, not even +<B>pthread_mutex_lock</B>, in spite of the fact that it can suspend a +thread for arbitrary durations. This way, the status of mutexes at +cancellation points is predictable, allowing cancellation handlers to +unlock precisely those mutexes that need to be unlocked before the +thread stops executing. Consequently, threads using deferred +cancellation should never hold a mutex for extended periods of time. +</P> +<H2><A HREF="#toc4" NAME="sect4">Async-signal Safety</A></H2> +<P>The mutex functions are not async-signal safe. What this means is +that they should not be called from a signal handler. In particular, +calling <B>pthread_mutex_lock</B> or <B>pthread_mutex_unlock</B> from +a signal handler may deadlock the calling thread. +</P> +<H2><A HREF="#toc5" NAME="sect5">Return Value</A></H2> +<P><B>pthread_mutex_init</B> always returns 0. The other mutex +functions return 0 on success and a non-zero error code on error. +</P> +<H2><A HREF="#toc6" NAME="sect6">Errors</A></H2> +<P>The <B>pthread_mutex_lock</B> function returns the following error +code on error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex has not been properly initialized. + </DD><DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + <B>EDEADLK</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex is already locked by the calling thread (‘‘error + checking’’ mutexes only). + </DD></DL> +</DL> +<P> +The <B>pthread_mutex_trylock</B> function returns the following error +codes on error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EBUSY</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex could not be acquired because it was currently locked. + </DD><DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + <B>EINVAL</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex has not been properly initialized. + </DD></DL> +</DL> +<P> +The <B>pthread_mutex_timedlock</B> function returns the following +error codes on error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>ETIMEDOUT</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex could not be acquired before the <I>abs_timeout</I> time + arrived. + </DD><DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + <B>EINVAL</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex has not been properly initialized. + </DD></DL> +</DL> +<P> +The <B>pthread_mutex_unlock</B> function returns the following error +code on error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex has not been properly initialized. + </DD><DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + <B>EPERM</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the calling thread does not own the mutex (‘‘error checking’’ + mutexes only). + </DD></DL> +</DL> +<P> +The <B>pthread_mutex_destroy</B> function returns the following error +code on error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EBUSY</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the mutex is currently locked. + </DD></DL> +</DL> +<H2> +<A HREF="#toc7" NAME="sect7">Author</A></H2> +<P>Xavier Leroy <Xavier.Leroy@inria.fr> +</P> +<P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P> +<H2><A HREF="#toc8" NAME="sect8">See Also</A></H2> +<P><A HREF="pthread_mutexattr_init.html"><B>pthread_mutexattr_init</B>(3)</A> +, <A HREF="pthread_mutexattr_init.html"><B>pthread_mutexattr_settype</B>(3)</A> +, <A HREF="pthread_cancel.html"><B>pthread_cancel</B>(3)</A> . +</P> +<H2><A HREF="#toc9" NAME="sect9">Example</A></H2> +<P>A shared global variable <I>x</I> can be protected by a mutex as +follows: +</P> +<PRE STYLE="margin-left: 1cm; margin-right: 1cm">int x; +pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;</PRE><BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"> +All accesses and modifications to <I>x</I> should be bracketed by +calls to <B>pthread_mutex_lock</B> and <B>pthread_mutex_unlock</B> as +follows: +</BLOCKQUOTE> +<PRE STYLE="margin-left: 1.03cm; margin-right: 2cm">pthread_mutex_lock(&mut); +/* operate on x */ +pthread_mutex_unlock(&mut);</PRE> +<HR> +<BLOCKQUOTE STYLE="margin-right: 4cm"><A NAME="toc"></A><B>Table of +Contents</B></BLOCKQUOTE> +<UL> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Cancellation</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Async-signal + Safety</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Return + Value</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">Errors</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect7" NAME="toc7">Author</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm; margin-bottom: 0cm"><A HREF="#sect8" NAME="toc8">See + Also</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 4cm"><A HREF="#sect9" NAME="toc9">Example</A> + </BLOCKQUOTE> +</UL> +</BODY> +</HTML> |