Linux多线程编程快速入门
<div id="navCategory"><h5 class="catalogue">目录</h5><ul class="first_class_ul"><li><span>1 线程基本知识</span>
</li><li>
<span>2. 线程标识</span>
</li><li>
<span>3. 线程创建</span>
</li><li>
<span>4. 线程终止</span>
</li><li>
<span>5. 管理线程的终止</span>
<ul class="second_class_ul"><li>
5.1 线程的连接</li><li>
5.2 线程的分离</li></ul></li><li>
<span>总结</span>
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<h5 class="catalogue">
目录</h5>
<ul class="first_class_ul">
<li>
5.1 线程的连接</li>
<li>
5.2 线程的分离</li>
</ul>
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<p>
本文主要对Linux下的多线程进行一个入门的介绍，虽然是入门，但是十分详细，希望大家通过本文所述，对Linux多线程编程的概念有一定的了解。具体如下。</p>
<p class="maodian"></p><h2>
<span>1 线程基本知识</span>
</h2>
<p>
进程是资源管理的基本单元，而线程是系统调度的基本单元，线程是操作系统能够进行调度运算的最小单位，它被包含在进程之中，是进程中的实际运作单位。一条线程指的是进程中一个单一顺序的控制流，一个进程中可以并发多个线程，每条线程并行执行不同的任务。</p>
<p>
一个进程在某一个时刻只能做一件事情，有了多个控制线程以后，在程序的设计成在某一个时刻能够做不止一件事，每个线程处理独自的任务。</p>
<p>
需要注意的是：即使程序运行在单核处理器上，也能够得到多线程编程模型的好处。处理器的数量并不影响程序结构，所以不管处理器个数多少，程序都可以通过线程得以简化。</p>
<p>
linux操作系统使用符合POSIX线程作为系统标准线程，该POSIX线程标准定义了一整套操作线程的API。</p>
<p class="maodian"></p><h2>
<span>2. 线程标识</span>
</h2>
<p>
与进程有一个ID一样，每个线程有一个线程ID，所不同的是，进程ID在整个系统中是唯一的，而线程是依附于进程的，其线程ID只有在所属的进程中才有意义。线程ID用pthread_t表示。</p>
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<code class="cpp comments">//pthread_self直接返回调用线程的ID</code>
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<code class="cpp plain">include <pthread.h></code>
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<code class="cpp plain">pthread_t pthread_self(</code><code class="cpp keyword bold">void</code><code class="cpp plain">);</code>
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判断两个线程ID的大小是没有任何意义的，但有时可能需要判断两个给定的线程ID是否相等，使用以下接口：</p>
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<code class="cpp comments">//pthread_equal如果t1和t2所指定的线程ID相同，返回0；否则返回非0值。</code>
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<code class="cpp plain">include <pthread.h></code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">pthread_equal(pthread_t t1, pthread_t t2);</code>
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<span>3. 线程创建</span>
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一个线程的生命周期起始于它被创建的那一刻，创建线程的接口：</p>
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<code class="cpp preprocessor">#include <pthread.h></code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">pthread_create(pthread_t *</code><code class="cpp keyword bold">thread</code><code class="cpp plain">, </code><code class="cpp keyword bold">const</code> <code class="cpp plain">pthread_attr_t *attr, </code>
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<code class="cpp keyword bold">void</code> <code class="cpp plain">*(*start_routine) (</code><code class="cpp keyword bold">void</code> <code class="cpp plain">*), </code><code class="cpp keyword bold">void</code> <code class="cpp plain">*arg);</code>
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函数参数：</p>
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<code class="plain plain">thread(输出参数)，由pthread_create在线程创建成功后返回的线程句柄，该句柄在后续操作线程的API中用于标志该新建的线程； </code>
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<code class="plain plain">start_routine(输入参数)，新建线程的入口函数； </code>
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<code class="plain plain">arg(输入参数)，传递给新线程入口函数的参数； </code>
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<code class="plain plain">attr(输入参数)，指定新建线程的属性，如线程栈大小等；如果值为NULL，表示使用系统默认属性。</code>
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函数返回值：</p>
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<code class="plain plain">成功，返回0； </code>
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<code class="plain plain">失败，返回相关错误码。</code>
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需要注意：</p>
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1.主线程，这是一个进程的初始线程，其入口函数为main函数。<br>
2.新线程的运行时机，一个线程被创建之后有可能不会被马上执行，甚至，在创建它的线程结束后还没被执行；也有可能新线程在当前线程从pthread_create前就已经在运行，甚至，在pthread_create前从当前线程返回前新线程就已经执行完毕。</p>
<p>
程序实例：</p>
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<code class="cpp spaces"> </code><code class="cpp plain">pid_t pid;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pthread_t tid;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pid = getpid();</code>
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<code class="cpp spaces"> </code><code class="cpp plain">tid = pthread_self();</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"%s, pid %lu tid %lu (0x%lx)\n"</code><code class="cpp plain">,s,(unsigned </code><code class="cpp color1 bold">long</code><code class="cpp plain">)pid,(unsigned </code><code class="cpp color1 bold">long</code><code class="cpp plain">)tid,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">(unsigned </code><code class="cpp color1 bold">long</code><code class="cpp plain">)tid);</code>
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<code class="cpp keyword bold">void</code> <code class="cpp plain">*thread_func(</code><code class="cpp keyword bold">void</code> <code class="cpp plain">*arg){</code>
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<code class="cpp spaces"> </code><code class="cpp plain">printids(</code><code class="cpp string">"new thread: "</code><code class="cpp plain">);</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main() {</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">err;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pthread_t tid;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">err = pthread_create(&tid,NULL,thread_func,NULL);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(err != 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stderr,</code><code class="cpp string">"create thread fail.\n"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">exit</code><code class="cpp plain">(-1); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">printids(</code><code class="cpp string">"main thread:"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">sleep(1); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">0;</code>
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注意上述的程序中，主线程休眠一秒，如果不休眠，则主线程不休眠，则其可能会退出，这样新线程可能不会被运行，我自己注释掉sleep函数，发现好多次才能让新线程输出。</p>
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编译命令：</p>
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<code class="cpp plain">gcc -o </code><code class="cpp keyword bold">thread</code> <code class="cpp keyword bold">thread</code><code class="cpp plain">.c -lpthread</code>
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运行结果如下：</p>
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<code class="cpp plain">main </code><code class="cpp keyword bold">thread</code><code class="cpp plain">:, pid 889 tid 139846854309696 (0x7f30a212f740)</code>
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<code class="cpp keyword bold">new</code> <code class="cpp keyword bold">thread</code><code class="cpp plain">: , pid 889 tid 139846845961984 (0x7f30a1939700)</code>
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可以看到两个线程的进程ID是相同的。其共享进程中的资源。</p>
<p class="maodian"></p><h2>
<span>4. 线程终止</span>
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<p>
线程的终止分两种形式：被动终止和主动终止</p>
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被动终止有两种方式：</p>
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1.线程所在进程终止，任意线程执行exit、_Exit或者_exit函数，都会导致进程终止，从而导致依附于该进程的所有线程终止。<br>
2.其他线程调用pthread_cancel请求取消该线程。</p>
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主动终止也有两种方式：</p>
<p>
1.在线程的入口函数中执行return语句，main函数(主线程入口函数)执行return语句会导致进程终止，从而导致依附于该进程的所有线程终止。<br>
2.线程调用pthread_exit函数，main函数(主线程入口函数)调用pthread_exit函数， 主线程终止，但如果该进程内还有其他线程存在，进程会继续存在，进程内其他线程继续运行。</p>
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线程终止函数：</p>
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线程调用pthread_exit函数会导致该调用线程终止，并且返回由retval指定的内容。<br>
注意:retval不能指向该线程的栈空间，否则可能成为野指针！</p>
<p class="maodian"></p><h2>
<span>5. 管理线程的终止</span>
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<p class="maodian">
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<p class="maodian"></p><h3>
5.1 线程的连接</h3>
<p>
一个线程的终止对于另外一个线程而言是一种异步的事件，有时我们想等待某个ID的线程终止了再去执行某些操作，pthread_join函数为我们提供了这种功能，该功能称为线程的连接：</p>
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<p>
参数说明：</p>
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<code class="plain plain">thread(输入参数)，指定我们希望等待的线程 </code>
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<code class="plain plain">retval(输出参数)，我们等待的线程终止时的返回值，就是在线程入口函数中return的值或者调用pthread_exit函数的参数</code>
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返回值：</p>
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<code class="plain plain">成功时，返回0 </code>
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<code class="plain plain">错误时，返回正数错误码</code>
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<p>
当线程X连接线程Y时，如果线程Y仍在运行，则线程X会阻塞直到线程Y终止；如果线程Y在被连接之前已经终止了，那么线程X的连接调用会立即返回。</p>
<p>
连接线程其实还有另外一层意义，一个线程终止后，如果没有人对它进行连接，那么该终止线程占用的资源，系统将无法回收，而该终止线程也会成为僵尸线程。因此，当我们去连接某个线程时，其实也是在告诉系统该终止线程的资源可以回收了。</p>
<p>
注意:对于一个已经被连接过的线程再次执行连接操作， 将会导致无法预知的行为！</p>
<p class="maodian">
</p>
<p class="maodian"></p><h3>
5.2 线程的分离</h3>
<p>
有时我们并不在乎某个线程是不是已经终止了，我们只是希望如果某个线程终止了，系统能自动回收掉该终止线程所占用的资源。pthread_detach函数为我们提供了这个功能，该功能称为线程的分离：</p>
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<code class="cpp preprocessor">#include <pthread.h></code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">pthread_detach(pthread_t </code><code class="cpp keyword bold">thread</code><code class="cpp plain">);</code>
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默认情况下，一个线程终止了，是需要在被连接后系统才能回收其占有的资源的。如果我们调用pthread_detach函数去分离某个线程，那么该线程终止后系统将自动回收其资源。</p>
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<code class="cpp comments">/*</code>
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<code class="cpp comments">* 文件名： thread_sample1.c</code>
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<code class="cpp comments">* 描述：演示线程基本操作</code>
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<code class="cpp comments">*/</code>
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<code class="cpp preprocessor">#include <stdio.h></code>
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<code class="cpp preprocessor">#include <stdlib.h></code>
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<code class="cpp preprocessor">#include <unistd.h></code>
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<code class="cpp preprocessor">#include <pthread.h></code>
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<code class="cpp comments">/*子线程1入口函数*/</code>
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<code class="cpp keyword bold">void</code> <code class="cpp plain">*thread_routine1(</code><code class="cpp keyword bold">void</code> <code class="cpp plain">*arg)</code>
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<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"thread1: hello world!\n"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">sleep(1);</code>
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<code class="cpp spaces"> </code><code class="cpp comments">/*子线程1在此退出*/</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">NULL;</code>
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<div class="line number17 index16 alt2">
<code class="cpp plain">}</code>
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</div>
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<code class="cpp comments">/*子线程2入口函数*/</code>
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<code class="cpp keyword bold">void</code> <code class="cpp plain">*thread_routine2(</code><code class="cpp keyword bold">void</code> <code class="cpp plain">*arg)</code>
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<div class="line number21 index20 alt2">
<code class="cpp plain">{</code>
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<div class="line number23 index22 alt2">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"thread2: I'm running...\n"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pthread_t main_thread = (pthread_t)arg;</code>
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<div class="line number25 index24 alt2">
</div>
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<code class="cpp spaces"> </code><code class="cpp comments">/*分离自我，不能再被连接*/</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pthread_detach(pthread_self());</code>
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<div class="line number28 index27 alt1">
</div>
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<code class="cpp spaces"> </code><code class="cpp comments">/*判断主线程ID与子线程2ID是否相等*/</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(!pthread_equal(main_thread, pthread_self())) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"thread2: main thread id is not equal thread2\n"</code><code class="cpp plain">);</code>
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<div class="line number32 index31 alt1">
<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<div class="line number33 index32 alt2">
</div>
<div class="line number34 index33 alt1">
<code class="cpp spaces"> </code><code class="cpp comments">/*等待主线程终止*/</code>
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<div class="line number35 index34 alt2">
<code class="cpp spaces"> </code><code class="cpp plain">pthread_join(main_thread, NULL);</code>
</div>
<div class="line number36 index35 alt1">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"thread2: main thread exit!\n"</code><code class="cpp plain">);</code>
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<div class="line number37 index36 alt2">
</div>
<div class="line number38 index37 alt1">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"thread2: exit!\n"</code><code class="cpp plain">);</code>
</div>
<div class="line number39 index38 alt2">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"thread2: process exit!\n"</code><code class="cpp plain">);</code>
</div>
<div class="line number40 index39 alt1">
<code class="cpp spaces"> </code><code class="cpp comments">/*子线程2在此终止，进程退出*/</code>
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<div class="line number41 index40 alt2">
<code class="cpp spaces"> </code><code class="cpp plain">pthread_exit(NULL);</code>
</div>
<div class="line number42 index41 alt1">
<code class="cpp plain">}</code>
</div>
<div class="line number43 index42 alt2">
</div>
<div class="line number44 index43 alt1">
<code class="cpp color1 bold">int</code> <code class="cpp plain">main(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">argc, </code><code class="cpp color1 bold">char</code> <code class="cpp plain">*argv[])</code>
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<div class="line number45 index44 alt2">
<code class="cpp plain">{</code>
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<div class="line number46 index45 alt1">
</div>
<div class="line number47 index46 alt2">
<code class="cpp spaces"> </code><code class="cpp comments">/*创建子线程1*/</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pthread_t t1;</code>
</div>
<div class="line number49 index48 alt2">
<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(pthread_create(&t1, NULL, thread_routine1, NULL)!=0) {</code>
</div>
<div class="line number50 index49 alt1">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stderr, </code><code class="cpp string">"create thread fail.\n"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">exit</code><code class="cpp plain">(-1);</code>
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<div class="line number52 index51 alt1">
<code class="cpp spaces"> </code><code class="cpp plain">}</code>
</div>
<div class="line number53 index52 alt2">
<code class="cpp spaces"> </code><code class="cpp comments">/*等待子线程1终止*/</code>
</div>
<div class="line number54 index53 alt1">
<code class="cpp spaces"> </code><code class="cpp plain">pthread_join(t1, NULL);</code>
</div>
<div class="line number55 index54 alt2">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"main thread: thread1 terminated!\n\n"</code><code class="cpp plain">);</code>
</div>
<div class="line number56 index55 alt1">
</div>
<div class="line number57 index56 alt2">
<code class="cpp spaces"> </code><code class="cpp comments">/*创建子线程2，并将主线程ID传递给子线程2*/</code>
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<div class="line number58 index57 alt1">
<code class="cpp spaces"> </code><code class="cpp plain">pthread_t t2;</code>
</div>
<div class="line number59 index58 alt2">
<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(pthread_create(&t2, NULL, thread_routine2, (</code><code class="cpp keyword bold">void</code> <code class="cpp plain">*)pthread_self())!=0) {</code>
</div>
<div class="line number60 index59 alt1">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stderr, </code><code class="cpp string">"create thread fail.\n"</code><code class="cpp plain">);</code>
</div>
<div class="line number61 index60 alt2">
<code class="cpp spaces"> </code><code class="cpp functions bold">exit</code><code class="cpp plain">(-1);</code>
</div>
<div class="line number62 index61 alt1">
<code class="cpp spaces"> </code><code class="cpp plain">}</code>
</div>
<div class="line number63 index62 alt2">
</div>
<div class="line number64 index63 alt1">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"main thread: sleeping...\n"</code><code class="cpp plain">);</code>
</div>
<div class="line number65 index64 alt2">
<code class="cpp spaces"> </code><code class="cpp plain">sleep(3);</code>
</div>
<div class="line number66 index65 alt1">
<code class="cpp spaces"> </code><code class="cpp comments">/*主线程使用pthread_exit函数终止，进程继续存在*/</code>
</div>
<div class="line number67 index66 alt2">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"main thread: exit!\n"</code><code class="cpp plain">);</code>
</div>
<div class="line number68 index67 alt1">
<code class="cpp spaces"> </code><code class="cpp plain">pthread_exit(NULL); </code>
</div>
<div class="line number69 index68 alt2">
</div>
<div class="line number70 index69 alt1">
<code class="cpp spaces"> </code><code class="cpp functions bold">fprintf</code><code class="cpp plain">(stdout, </code><code class="cpp string">"main thread: never reach here!\n"</code><code class="cpp plain">);</code>
</div>
<div class="line number71 index70 alt2">
<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">0;</code>
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<div class="line number72 index71 alt1">
<code class="cpp plain">}</code>
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<div class="codetool" id="codetool">
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<textarea></textarea>
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<p>
最终的执行结果如下：</p>
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<code class="cpp plain">thread1: hello world!</code>
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<code class="cpp plain">main </code><code class="cpp keyword bold">thread</code><code class="cpp plain">: thread1 terminated!</code>
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<code class="cpp plain">main </code><code class="cpp keyword bold">thread</code><code class="cpp plain">: sleeping...</code>
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<code class="cpp plain">thread2: I'm running...</code>
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<div class="line number6 index5 alt1">
<code class="cpp plain">thread2: main </code><code class="cpp keyword bold">thread</code> <code class="cpp plain">id is not equal thread2</code>
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<code class="cpp plain">main </code><code class="cpp keyword bold">thread</code><code class="cpp plain">: </code><code class="cpp functions bold">exit</code><code class="cpp plain">!</code>
</div>
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<code class="cpp plain">thread2: main </code><code class="cpp keyword bold">thread</code> <code class="cpp functions bold">exit</code><code class="cpp plain">!</code>
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<code class="cpp plain">thread2: </code><code class="cpp functions bold">exit</code><code class="cpp plain">!</code>
</div>
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<code class="cpp plain">thread2: process </code><code class="cpp functions bold">exit</code><code class="cpp plain">!</code>
</div>
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</td>
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</div>
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<div class="codetool" id="codetool">
<div class="code_n">
<textarea></textarea>
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<p class="maodian"></p><h2>
<span>总结</span>
</h2>
<p>
以上就是本文关于Linux多线程编程快速入门的全部内容，希望对大家有所帮助。感兴趣的朋友可以继续参阅本站其他相关专题，如有不足之处，欢迎留言指出。感谢朋友们对本站的支持！</p>
<p>
原文链接：http://blog.csdn.net/taoyanqi8932/article/details/56288950</p>
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