📄 posix线程编程指南(5).htm
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<TD><A class=left-nav-child
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<H1>Posix线程编程指南(5)</H1>
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<FORM name=email
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value=这是一个关于Posix线程编程的专栏。作者在阐明概念的基础上，将向您详细讲述Posix线程库API。本文是第五篇将向您讲述pthread_self()、pthread_equal()和pthread_once()等杂项函数。
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<P>级别: 初级</P>
<P><A
href="http://www-128.ibm.com/developerworks/cn/linux/thread/posix_threadapi/part5/#author">杨沙洲</A>
<BR></P>
<P>2001 年 11 月 01 日</P>
<BLOCKQUOTE>这是一个关于Posix线程编程的专栏。作者在阐明概念的基础上，将向您详细讲述Posix线程库API。本文是第五篇将向您讲述pthread_self()、pthread_equal()和pthread_once()等杂项函数。</BLOCKQUOTE><!--START RESERVED FOR FUTURE USE INCLUDE FILES--><!-- include java script once we verify teams wants to use this and it will work on dbcs and cyrillic characters --><!--END RESERVED FOR FUTURE USE INCLUDE FILES-->
<P>在Posix线程规范中还有几个辅助函数难以归类，暂且称其为杂项函数，主要包括pthread_self()、pthread_equal()和pthread_once()三个，另外还有一个LinuxThreads非可移植性扩展函数pthread_kill_other_threads_np()。本文就介绍这几个函数的定义和使用。</P>
<P><A name=1><SPAN class=atitle>获得本线程ID</SPAN></A></P>
<P>
<P>pthread_t pthread_self(void)</P>
<P>本函数返回本线程的标识符。</P>
<P>在LinuxThreads中，每个线程都用一个pthread_descr结构来描述，其中包含了线程状态、线程ID等所有需要的数据结构，此函数的实现就是在线程栈帧中找到本线程的pthread_descr结构，然后返回其中的p_tid项。</P>
<P>pthread_t类型在LinuxThreads中定义为无符号长整型。</P><BR>
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<P><A name=2><SPAN class=atitle>判断两个线程是否为同一线程</SPAN></A></P>
<P>
<P>int pthread_equal(pthread_t thread1, pthread_t thread2)</P>
<P>判断两个线程描述符是否指向同一线程。在LinuxThreads中，线程ID相同的线程必然是同一个线程，因此，这个函数的实现仅仅判断thread1和thread2是否相等。</P><BR>
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<P><A name=3><SPAN class=atitle>仅执行一次的操作</SPAN></A></P>
<P>
<P>int pthread_once(pthread_once_t *once_control, void
(*init_routine) (void))</P>
<P>本函数使用初值为PTHREAD_ONCE_INIT的once_control变量保证init_routine()函数在本进程执行序列中仅执行一次。</P>
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<TD><PRE><CODE class=section>#include <stdio.h>
#include <pthread.h>
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