POSIX 多线程程序设计

电玩女神 2022-08-14 04:46 164阅读 0赞

*Blaise Barney, Lawrence Livermore National Laboratory*

[http://download.csdn.net/detail/xiaoyao333000/6994423][http_download.csdn.net_detail_xiaoyao333000_6994423]程序员的自我修养

**目录表 **

1.  [摘要][Link 1]  
2.  [译者序][Link 2]
3.  [Pthreads 概述 ][Pthreads] 
    
    1.  [什么是线程?  ][Link 3]
    2.  [什么是Pthreads?  ][Pthreads_]
    3.  [为什么使用Pthreads? ][Pthreads 1] 
    4.  [使用线程设计程序  ][Link 4]
4.  [Pthreads API编译多线程程序 ][Pthreads API] 
5.  [线程管理  ][Link 5]
    
    1.  [创建和终止线程 ][Link 6] 
    2.  [向线程传递参数 ][Link 7] 
    3.  [连接（Joining）和分离（ Detaching）线程  ][Joining_ Detaching_]
    4.  [栈管理  ][Link 8]
    5.  [其它函数 ][Link 9] 
6.  [互斥量（Mutex Variables）][Mutex Variables]  
    
    1.  [互斥量概述 ][Link 10] 
    2.  [创建和销毁互斥量  ][Link 11]
    3.  [锁定（Locking）和解锁（Unlocking）互斥量 ][Locking_Unlocking] 
7.  [条件变量（Condition Variable）][Condition Variable]  
    
    1.  [条件变量概述 ][Link 12]
    2.  [创建和销毁条件变量  ][Link 13]
    3.  [等待（Waiting）和发送信号（Signaling）][Waiting_Signaling]  
8.  [没有覆盖的主题  ][Link 14]
9.  [Pthread 库API参考 ][Pthread _API] 
10. [参考资料][Link 15][ ][Link 15]

在多处理器共享内存的架构中（如：对称多处理系统SMP），线程可以用于实现程序的并行性。历史上硬件销售商实现了各种私有版本的多线程库，使得软件开发者不得不关心它的移植性。对于UNIX系统，IEEE POSIX 1003.1标准定义了一个C语言多线程编程接口。依附于该标准的实现被称为POSIX theads 或 Pthreads。

该教程介绍了Pthreads的概念、动机和设计思想。内容包含了Pthreads API主要的三大类函数：线程管理（Thread Managment）、互斥量（Mutex Variables）和条件变量（Condition Variables）。向刚开始学习Pthreads的程序员提供了演示例程。

适于：刚开始学习使用线程实现并行程序设计；对于C并行程序设计有基本了解。不熟悉并行程序设计的可以参考[EC3500: Introduction To Parallel Computing][EC3500_ Introduction To Parallel Computing]。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a rel="nofollow"></a>Pthreads 概述&nbsp;</td> 
 </tr> 
 </tbody> 
</table>

**什么是线程? **

*  技术上，线程可以定义为：可以被操作系统调度的独立的指令流。但是这是什么意思呢？ 
 *  对于软件开发者，在主程序中运行的“函数过程”可以很好的描述线程的概念。 
 *  进一步，想象下主程序（a.out）包含了许多函数，操作系统可以调度这些函数，使之同时或者（和）独立的执行。这就描述了“多线程”程序。 
 *  怎样完成的呢？

*  在理解线程之前，应先对UNIX进程（process）有所了解。进程被操作系统创建，需要相当多的“额外开销”。进程包含了程序的资源和执行状态信息。如下： 
    
     *  进程ID，进程group ID，用户ID和group ID 
     *  环境 
     *  工作目录  
     *  程序指令 
     *  寄存器 
     *  栈 
     *  堆 
     *  文件描述符 
     *  信号动作（Signal actions） 
     *  共享库 
     *  进程间通信工具（如：消息队列，管道，信号量或共享内存）

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> &nbsp;&nbsp;&nbsp;<img height="406" width="330" alt="Unix Process" src="https://computing.llnl.gov/tutorials/pthreads/images/process.gif"> </td> 
 <td> &nbsp;<img height="398" width="340" alt="Process-thread relationship" src="https://computing.llnl.gov/tutorials/pthreads/images/thread.gif"> </td> 
 </tr> 
 <tr> 
 <td> UNIX PROCESS&nbsp; </td> 
 <td> THREADS WITHIN A UNIX PROCESS&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

*  线程使用并存在于进程资源中，还可以被操作系统调用并独立地运行，这主要是因为线程仅仅复制必要的资源以使自己得以存在并执行。 
 *  独立的控制流得以实现是因为线程维持着自己的： 
    
     *  堆栈指针 
     *  寄存器 
     *  调度属性（如：策略或优先级） 
     *  待定的和阻塞的信号集合（Set of pending and blocked signals） 
     *  线程专用数据（TSD：Thread Specific Data.） 
 *  因此，在UNIX环境下线程： 
    
     *  存在于进程，使用进程资源 
     *  拥有自己独立的控制流，只要父进程存在并且操作系统支持 
     *  只复制必可以使得独立调度的必要资源 
     *  可以和其他线程独立（或非独立的）地共享进程资源 
     *  当父进程结束时结束，或者相关类似的 
     *  是“轻型的”，因为大部分额外开销已经在进程创建时完成了 
 *  因为在同一个进程中的线程共享资源： 
    
     *  一个线程对系统资源（如关闭一个文件）的改变对所有其它线程是可以见的 
     *  两个同样值的指针指向相同的数据 
     *  读写同一个内存位置是可能的，因此需要成员显式地使用同步

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Pthreads&nbsp;概述&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**什么是 Pthreads? **

*  历史上，硬件销售商实现了私有版本的多线程库。这些实现在本质上各自不同，使得程序员难于开发可移植的应用程序。 
 *  为了使用线程所提供的强大优点，需要一个标准的程序接口。对于UNIX系统，IEEE POSIX 1003.1c（1995）标准制订了这一标准接口。依赖于该标准的实现就称为POSIX threads 或者Pthreads。现在多数硬件销售商也提供Pthreads，附加于私有的API。 
 *  Pthreads 被定义为一些C语言类型和函数调用，用pthread.h头（包含）文件和线程库实现。这个库可以是其它库的一部分，如libc。

**为什么使用 Pthreads? **

*  使用Pthreads的主要动机是提高潜在程序的性能。 
 *  当与创建和管理进程的花费相比，线程可以使用操作系统较少的开销，管理线程需要较少的系统资源。

例如，下表比较了fork()函数和pthread\_create()函数所用的时间。计时反应了50,000个进程/线程的创建，使用时间工具实现，单位是秒，没有优化标志。

备注：不要期待系统和用户时间加起来就是真实时间，因为这些SMP系统有多个CPU同时工作。这些都是近似值。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> 平台&nbsp; </td> 
 <td colspan="3"> fork()&nbsp; </td> 
 <td colspan="3"> pthread_create()&nbsp; </td> 
 </tr> 
 <tr> 
 <td> real&nbsp; </td> 
 <td> user&nbsp; </td> 
 <td> sys&nbsp; </td> 
 <td> real&nbsp; </td> 
 <td> user&nbsp; </td> 
 <td> sys&nbsp; </td> 
 </tr> 
 <tr> 
 <td> AMD 2.4 GHz Opteron (8cpus/node)&nbsp;&nbsp; </td> 
 <td> 41.07&nbsp; </td> 
 <td> 60.08&nbsp; </td> 
 <td> 9.01&nbsp; </td> 
 <td> 0.66&nbsp; </td> 
 <td> 0.19&nbsp; </td> 
 <td> 0.43&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM 1.9 GHz POWER5 p5-575 (8cpus/node)&nbsp;&nbsp; </td> 
 <td> 64.24&nbsp; </td> 
 <td> 30.78&nbsp; </td> 
 <td> 27.68&nbsp; </td> 
 <td> 1.75&nbsp; </td> 
 <td> 0.69&nbsp; </td> 
 <td> 1.10&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM 1.5 GHz POWER4 (8cpus/node)&nbsp;&nbsp; </td> 
 <td> 104.05&nbsp; </td> 
 <td> 48.64&nbsp; </td> 
 <td> 47.21&nbsp; </td> 
 <td> 2.01&nbsp; </td> 
 <td> 1.00&nbsp; </td> 
 <td> 1.52&nbsp; </td> 
 </tr> 
 <tr> 
 <td> INTEL 2.4 GHz Xeon (2 cpus/node)&nbsp;&nbsp; </td> 
 <td> 54.95&nbsp; </td> 
 <td> 1.54&nbsp; </td> 
 <td> 20.78&nbsp; </td> 
 <td> 1.64&nbsp; </td> 
 <td> 0.67&nbsp; </td> 
 <td> 0.90&nbsp; </td> 
 </tr> 
 <tr> 
 <td> INTEL 1.4 GHz Itanium2 (4 cpus/node)&nbsp;&nbsp; </td> 
 <td> 54.54&nbsp; </td> 
 <td> 1.07&nbsp; </td> 
 <td> 22.22&nbsp; </td> 
 <td> 2.03&nbsp; </td> 
 <td> 1.26&nbsp; </td> 
 <td> 0.67&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

[fork\_vs\_thread.txt][fork_vs_thread.txt]

*  在同一个进程中的所有线程共享同样的地址空间。较于进程间的通信，在许多情况下线程间的通信效率比较高，且易于使用。 
 *  较于没有使用线程的程序，使用线程的应用程序有潜在的性能增益和实际的优点： 
    
     *  CPU使用I/O交叠工作：例如，一个程序可能有一个需要较长时间的I/O操作，当一个线程等待I/O系统调用完成时，CPU可以被其它线程使用。 
     *  优先/实时调度：比较重要的任务可以被调度，替换或者中断较低优先级的任务。 
     *  异步事件处理：频率和持续时间不确定的任务可以交错。例如，web服务器可以同时为前一个请求传输数据和管理新请求。 
 *  考虑在SMP架构上使用Pthreads的主要动机是获的最优的性能。特别的，如果一个程序使用MPI在节点通信，使用Pthreads可以使得节点数据传输得到显著提高。 
 *  例如： 
    
     *  MPI库经常用共享内存实现节点任务通信，这至少需要一次内存复制操作（进程到进程）。 
     *  Pthreads没有中间的内存复制，因为线程和一个进程共享同样的地址空间。没有数据传输。变成cache-to-CPU或memory-to-CPU的带宽（最坏情况），速度是相当的快。 
     *  比较如下：

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Platform&nbsp; </td> 
 <td> MPI Shared Memory Bandwidth (GB/sec)&nbsp; </td> 
 <td> Pthreads Worst Case Memory-to-CPU Bandwidth&nbsp; (GB/sec)&nbsp; </td> 
 </tr> 
 <tr> 
 <td> AMD 2.4 GHz Opteron &nbsp; </td> 
 <td> 1.2&nbsp; </td> 
 <td> 5.3&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM 1.9 GHz POWER5 p5-575 &nbsp; </td> 
 <td> 4.1&nbsp; </td> 
 <td> 16&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM 1.5 GHz POWER4 &nbsp; </td> 
 <td> 2.1&nbsp; </td> 
 <td> 4&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Intel 1.4 GHz Xeon &nbsp; </td> 
 <td> 0.3&nbsp; </td> 
 <td> 4.3&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Intel 1.4 GHz Itanium 2 &nbsp; </td> 
 <td> 1.8&nbsp; </td> 
 <td> 6.4&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**使用线程设计程序 **

**并行编程:**

*  在现代多CPU机器上，pthread非常适于并行编程。可以用于并行程序设计的，也可以用于pthread程序设计。 
 *  并行程序要考虑许多，如下： 
    
     *  用什么并行程序设计模型？ 
     *  问题划分 
     *  加载平衡（Load balancing） 
     *  通信 
     *  数据依赖 
     *  同步和竞争条件 
     *  内存问题 
     *  I/O问题 
     *  程序复杂度 
     *  程序员的努力/花费/时间 
     *  ...  
 *  包含这些主题超出本教程的范围，有兴趣的读者可以快速浏览下“[Introduction to Parallel Computing][EC3500_ Introduction To Parallel Computing]”教程。 
 *  大体上，为了使用Pthreads的优点，必须将任务组织程离散的，独立的，可以并发执行的。例如，如果routine1和routine2可以互换，相互交叉和（或者）重叠，他们就可以线程化。

*  拥有下述特性的程序可以使用pthreads： 
    
     *  工作可以被多个任务同时执行，或者数据可以同时被多个任务操作。 
     *  阻塞与潜在的长时间I/O等待。 
     *  在某些地方使用很多CPU循环而其他地方没有。 
     *  对异步事件必须响应。 
     *  一些工作比其他的重要（优先级中断）。 
 *  Pthreads 也可以用于串行程序，模拟并行执行。很好例子就是经典的web浏览器，对于多数人，运行于单CPU的桌面/膝上机器，许多东西可以同时“显示”出来。 
 *  使用线程编程的几种常见模型： 
    
     *  ***管理者/工作者（Manager/worker）：***一个单线程，作为管理器将工作分配给其它线程（工作者），典型的，管理器处理所有输入和分配工作给其它任务。至少两种形式的manager/worker模型比较常用：静态worker池和动态worker池。 
     *  ***管道（Pipeline）：***任务可以被划分为一系列子操作，每一个被串行处理，但是不同的线程并发处理。汽车装配线可以很好的描述这个模型。 
     *  ***Peer:*** 和manager/worker模型相似，但是主线程在创建了其它线程后，自己也参与工作。

**共享内存模型（Shared Memory Model）:**

*  所有线程可以访问全局，共享内存 
 *  线程也有自己私有的数据 
 *  程序员负责对全局共享数据的同步存取（保护）

**线程安全（Thread-safeness）:**

*  线程安全：简短的说，指程序可以同时执行多个线程却不会“破坏“共享数据或者产生“竞争”条件的能力。 
 *  例如：假设你的程序创建了几个线程，每一个调用相同的库函数： 
    
     *  这个库函数存取/修改了一个全局结构或内存中的位置。 
     *  当每个线程调用这个函数时，可能同时去修改这个全局结构活内存位置。 
     *  如果函数没有使用同步机制去阻止数据破坏，这时，就不是线程安全的了。

*  如果你不是100%确定外部库函数是线程安全的，自己负责所可能引发的问题。 
 *  建议：小心使用库或者对象，当不能明确确定是否是线程安全的。若有疑虑，假设其不是线程安全的直到得以证明。可以通过不断地使用不确定的函数找出问题所在。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a rel="nofollow"></a>Pthreads API&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

*  Pthreads API在ANSI/IEEE POSIX 1003.1 – 1995标准中定义。不像MPI，该标准不是免费的，必须向IEEE购买。 
 *  Pthreads API中的函数可以非正式的划分为三大类： 
    
    1.  ***线程管理（Thread management）:*** 第一类函数直接用于线程：创建（creating），分离（detaching），连接（joining）等等。包含了用于设置和查询线程属性（可连接，调度属性等）的函数。 
    2.  ***互斥量（Mutexes）:*** 第二类函数是用于线程同步的，称为互斥量（mutexes），是"mutual exclusion"的缩写。Mutex函数提供了创建，销毁，锁定和解锁互斥量的功能。同时还包括了一些用于设定或修改互斥量属性的函数。 
    3.  ***条件变量（Condition variables）：***第三类函数处理共享一个互斥量的线程间的通信，基于程序员指定的条件。这类函数包括指定的条件变量的创建，销毁，等待和受信（signal）。设置查询条件变量属性的函数也包含其中。 
 *  命名约定：线程库中的所有标识符都以**pthread**开头

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Routine Prefix&nbsp; </td> 
 <td> Functional Group&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_&nbsp; </td> 
 <td> 线程本身和各种相关函数&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_attr_&nbsp; </td> 
 <td> 线程属性对象&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_mutex_&nbsp; </td> 
 <td> 互斥量&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_mutexattr_&nbsp; </td> 
 <td> 互斥量属性对象&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_cond_&nbsp; </td> 
 <td> 条件变量&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_condattr_&nbsp; </td> 
 <td> 条件变量属性对象&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_key_&nbsp; </td> 
 <td> 线程数据键（Thread-specific data keys）&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

*  在API的设计中充满了不透明对象的概念，基本调用可以创建或修改不透明对象。不透明的对象可以被一些属性函数调用修改。 
 *  Pthread API包含了60多个函数。该教程仅限于一部分（对于刚开始学习Pthread的程序是非常有用的）。 
 *  为了可移植性，使用Pthread库时，pthread.h头文件必须在每个源文件中包含。 
 *  现行POSIX标准仅定义了C语言的使用。Fortran程序员可以嵌入C函数调用使用，有些Fortran编译器（像IBM AIX Fortran）可能提供了Fortran pthreads API。 
 *  关于Pthreads有些比较优秀的书籍。其中一些在该教程的参考一节列出。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a style="color:rgb(0,0,0)" rel="nofollow"></a>编译多线程程序&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

*  下表列出了一些编译使用了pthreads库程序的命令：

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Compiler / Platform&nbsp; </td> 
 <td> Compiler Command&nbsp; </td> 
 <td> Description&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM&nbsp; AIX&nbsp; </td> 
 <td> xlc_r &nbsp;/&nbsp; cc_r&nbsp; </td> 
 <td> C (ANSI &nbsp;/&nbsp; non-ANSI)&nbsp; </td> 
 </tr> 
 <tr> 
 <td> xlC_r&nbsp; </td> 
 <td> C++&nbsp; </td> 
 </tr> 
 <tr> 
 <td> xlf_r -qnosave xlf90_r -qnosave&nbsp; </td> 
 <td> Fortran - using IBM's Pthreads API (non-portable)&nbsp; </td> 
 </tr> 
 <tr> 
 <td> INTEL Linux&nbsp; </td> 
 <td> icc -pthread&nbsp; </td> 
 <td> C&nbsp; </td> 
 </tr> 
 <tr> 
 <td> icpc -pthread&nbsp; </td> 
 <td> C++&nbsp; </td> 
 </tr> 
 <tr> 
 <td> PathScale Linux&nbsp; </td> 
 <td> pathcc -pthread&nbsp; </td> 
 <td> C&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pathCC -pthread&nbsp; </td> 
 <td> C++&nbsp; </td> 
 </tr> 
 <tr> 
 <td> PGI Linux&nbsp; </td> 
 <td> pgcc -lpthread&nbsp; </td> 
 <td> C&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pgCC -lpthread&nbsp; </td> 
 <td> C++&nbsp; </td> 
 </tr> 
 <tr> 
 <td> GNU Linux, AIX&nbsp; </td> 
 <td> gcc -pthread&nbsp; </td> 
 <td> GNU C&nbsp; </td> 
 </tr> 
 <tr> 
 <td> g++ -pthread&nbsp; </td> 
 <td> GNU C++&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a rel="nofollow"></a>线程管理（Thread Management）&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**创建和结束线程 **

**函数：**

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_create.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_create</a>&nbsp;(thread,attr,start_routine,arg) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_exit.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_exit</a>&nbsp;(status)&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_init</a>&nbsp;(attr) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_destroy</a>&nbsp;(attr)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**创建线程:**

*  最初，main函数包含了一个缺省的线程。其它线程则需要程序员显式地创建。 
 *  pthread\_create 创建一个新线程并使之运行起来。该函数可以在程序的任何地方调用。 
 *  pthread\_create参数： 
    
     *  thread：返回一个不透明的，唯一的新线程标识符。 
     *  attr：不透明的线程属性对象。可以指定一个线程属性对象，或者NULL为缺省值。 
     *  start\_routine：线程将会执行一次的C函数。 
     *  arg: 传递给*start\_routine*单个参数，传递时必须转换成指向void的指针类型。没有参数传递时，可设置为NULL。 
 *  一个进程可以创建的线程最大数量取决于系统实现。 
 *  一旦创建，线程就称为peers，可以创建其它线程。线程之间没有指定的结构和依赖关系。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> &nbsp; </td> 
 <td> &nbsp; </td> 
 <td> Q：一个线程被创建后，怎么知道操作系统何时调度该线程使之运行？&nbsp; A：除非使用了Pthreads的调度机制，否则线程何时何地被执行取决于操作系统的实现。强壮的程序应该不依赖于线程执行的顺序。 &nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**线程属性:**

*  线程被创建时会带有默认的属性。其中的一些属性可以被程序员用线程属性对象来修改。 
 *  pthread\_attr\_init 和 pthread\_attr\_destroy用于初始化/销毁先成属性对象。 
 *  其它的一些函数用于查询和设置线程属性对象的指定属性。 
 *  一些属性下面将会讨论。

**结束终止:**

*  结束线程的方法有一下几种： 
    
     *  线程从主线程（main函数的初始线程）返回。 
     *  线程调用了pthread\_exit函数。 
     *  其它线程使用 pthread\_cancel函数结束线程。 
     *  调用exec或者exit函数，整个进程结束。 
 *  pthread\_exit用于显式退出线程。典型地，pthread\_exit()函数在线程完成工作时，不在需要时候被调用，退出线程。 
 *  如果main()在其他线程创建前用pthread\_exit()退出了，其他线程将会继续执行。否则，他们会随着main的结束而终止。 
 *  程序员可以可选择的指定终止状态，当任何线程连接（join）该线程时，该状态就返回给连接（join）该线程的线程。 
 *  清理：pthread\_exit()函数并不会关闭文件，任何在线程中打开的文件将会一直处于打开状态，知道线程结束。 
 *  讨论：对于正常退出，可以免于调用pthread\_exit()。当然，除非你想返回一个返回值。然而，在main中，有一个问题，就是当main结束时，其它线程还没有被创建。如果此时没有显式的调用pthread\_exit()，当main结束时，进程（和所有线程）都会终止。可以在main中调用pthread\_exit()，此时尽管在main中已经没有可执行的代码了，进程和所有线程将保持存活状态，。

--------------------

**例子: Pthread 创建和终止 **

*  该例用pthread\_create()创建了5个线程。每一个线程都会打印一条“Hello World”的消息，然后调用pthread\_exit()终止线程。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example Code - Pthread Creation and Termination&nbsp;&nbsp; #include &lt;pthread.h&gt;&nbsp; #include &lt;stdio.h&gt;&nbsp; #define NUM_THREADS&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5&nbsp; &nbsp; void *PrintHello(void *threadid)&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;int tid;&nbsp; &nbsp;&nbsp;&nbsp;tid = (int)threadid;&nbsp; &nbsp;&nbsp;&nbsp;printf("Hello World! It's me, thread #%d!\n", tid);&nbsp; &nbsp;&nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp; &nbsp; int main (int argc, char *argv[])&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;pthread_t threads[NUM_THREADS];&nbsp; &nbsp;&nbsp;&nbsp;int rc, t;&nbsp; &nbsp;&nbsp;&nbsp;for(t=0; t&lt;NUM_THREADS; t++){&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("In main: creating thread %d\n", t);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rc = pthread_create(&amp;threads[t], NULL, PrintHello, (void *)t);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (rc){&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("ERROR; return code from pthread_create() is %d\n", rc);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exit(-1);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello.c" style="color:rgb(0,0,0)" rel="nofollow"></a><a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello.out" style="color:rgb(0,0,0)" rel="nofollow"></a>&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**向线程传递参数 **

*  pthread\_create()函数允许程序员想线程的start routine传递一个参数。当多个参数需要被传递时，可以通过定义一个结构体包含所有要传的参数，然后用pthread\_create()传递一个指向改结构体的指针，来打破传递参数的个数的限制。 
 *  所有参数都应该传引用传递并转化成（void\*）。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> &nbsp; </td> 
 <td> &nbsp; </td> 
 <td> Q：怎样安全地向一个新创建的线程传递数据？&nbsp; A：确保所传递的数据是线程安全的（不能被其他线程修改）。下面三个例子演示了那个应该和那个不应该。&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example 1 - Thread Argument Passing&nbsp;&nbsp; 下面的代码片段演示了如何向一个线程传递一个简单的整数。主线程为每一个线程使用一个唯一的数据结构，确保每个线程传递的参数是完整的。&nbsp; 
 <div> 
 <hr> 
 </div> int *taskids[NUM_THREADS];&nbsp; &nbsp; for(t=0; t&lt;NUM_THREADS; t++)&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;taskids[t] = (int *) malloc(sizeof(int));&nbsp; &nbsp;&nbsp;&nbsp;*taskids[t] = t;&nbsp; &nbsp;&nbsp;&nbsp;printf("Creating thread %d\n", t);&nbsp; &nbsp;&nbsp;&nbsp;rc = pthread_create(&amp;threads[t], NULL, PrintHello, &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(void *) taskids[t]);&nbsp; &nbsp;&nbsp;&nbsp;...&nbsp; }&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello_arg1.c" style="color:rgb(0,0,0)" rel="nofollow"></a><a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello_arg1.out" style="color:rgb(0,0,0)" rel="nofollow"></a>&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example 2 - Thread Argument Passing&nbsp;&nbsp; 例子展示了用结构体向线程设置/传递参数。每个线程获得一个唯一的结构体实例。&nbsp; 
 <div> 
 <hr> 
 </div> struct thread_data{&nbsp; &nbsp;&nbsp;&nbsp;int&nbsp;&nbsp;thread_id;&nbsp; &nbsp;&nbsp;&nbsp;int&nbsp;&nbsp;sum;&nbsp; &nbsp;&nbsp;&nbsp;char *message;&nbsp; };&nbsp; &nbsp; struct thread_data thread_data_array[NUM_THREADS];&nbsp; &nbsp; void *PrintHello(void *threadarg)&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;struct thread_data *my_data;&nbsp; &nbsp;&nbsp;&nbsp;...&nbsp; &nbsp;&nbsp;&nbsp;my_data = (struct thread_data *) threadarg;&nbsp; &nbsp;&nbsp;&nbsp;taskid = my_data-&gt;thread_id;&nbsp; &nbsp;&nbsp;&nbsp;sum = my_data-&gt;sum;&nbsp; &nbsp;&nbsp;&nbsp;hello_msg = my_data-&gt;message;&nbsp; &nbsp;&nbsp;&nbsp;...&nbsp; }&nbsp; &nbsp; int main (int argc, char *argv[])&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;...&nbsp; &nbsp;&nbsp;&nbsp;thread_data_array[t].thread_id = t;&nbsp; &nbsp;&nbsp;&nbsp;thread_data_array[t].sum = sum;&nbsp; &nbsp;&nbsp;&nbsp;thread_data_array[t].message = messages[t];&nbsp; &nbsp;&nbsp;&nbsp;rc = pthread_create(&amp;threads[t], NULL, PrintHello, &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(void *) &amp;thread_data_array[t]);&nbsp; &nbsp;&nbsp;&nbsp;...&nbsp; }&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello_arg2.c" style="color:rgb(0,0,0)" rel="nofollow"></a><a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello_arg2.out" style="color:rgb(0,0,0)" rel="nofollow"></a>&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example 3 - Thread Argument Passing&nbsp;(Incorrect)&nbsp;&nbsp; 例子演示了错误地传递参数。循环会在线程访问传递的参数前改变传递给线程的地址的内容。&nbsp; 
 <div> 
 <hr> 
 </div> int rc, t;&nbsp; &nbsp; for(t=0; t&lt;NUM_THREADS; t++) &nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;printf("Creating thread %d\n", t);&nbsp; &nbsp;&nbsp;&nbsp;rc = pthread_create(&amp;threads[t], NULL, PrintHello, &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(void *) &amp;t);&nbsp; &nbsp;&nbsp;&nbsp;...&nbsp; }&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello_arg3.c" style="color:rgb(0,0,0)" rel="nofollow"></a><a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello_arg3.out" style="color:rgb(0,0,0)" rel="nofollow"></a>&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**连接（Joining）和分离（Detaching）线程 **

**函数:**

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_join.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_join</a>&nbsp;(threadid,status) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_detach.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_detach</a>&nbsp;(threadid,status)&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setdetachstate.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setdetachstate</a>&nbsp;(attr,detachstate) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getdetachstate.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getdetachstate</a>&nbsp;(attr,detachstate)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**连接:**

*   “连接”是一种在线程间完成同步的方法。例如：

*  pthread\_join()函数阻赛调用线程知道threadid所指定的线程终止。 
 *  如果在目标线程中调用pthread\_exit()，程序员可以在主线程中获得目标线程的终止状态。 
 *  连接线程只能用pthread\_join()连接一次。若多次调用就会发生逻辑错误。 
 *  两种同步方法，互斥量（mutexes）和条件变量（condition variables），稍后讨论。

**可连接（Joinable or Not）?**

*  当一个线程被创建，它有一个属性定义了它是可连接的（joinable）还是分离的（detached）。只有是可连接的线程才能被连接（joined），若果创建的线程是分离的，则不能连接。 
 *  POSIX标准的最终草案指定了线程必须创建成可连接的。然而，并非所有实现都遵循此约定。 
 *  使用pthread\_create()的attr参数可以显式的创建可连接或分离的线程，典型四步如下： 
    
    1.  声明一个pthread\_attr\_t数据类型的线程属性变量 
    2.  用 pthread\_attr\_init()初始化改属性变量 
    3.  用pthread\_attr\_setdetachstate()设置可分离状态属性 
    4.  完了后，用pthread\_attr\_destroy()释放属性所占用的库资源

**分离（Detaching）：**

*  pthread\_detach()可以显式用于分离线程，尽管创建时是可连接的。 
 *  没有与pthread\_detach()功能相反的函数

**建议：**

*  若线程需要连接，考虑创建时显式设置为可连接的。因为并非所有创建线程的实现都是将线程创建为可连接的。 
 *  若事先知道线程从不需要连接，考虑创建线程时将其设置为可分离状态。一些系统资源可能需要释放。

--------------------

**例子: Pthread Joining **

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example Code - Pthread Joining&nbsp;&nbsp; 这个例子演示了用Pthread join函数去等待线程终止。因为有些实现并不是默认创建线程是可连接状态，例子中显式地将其创建为可连接的。&nbsp;&nbsp; 
 <div> 
 <hr> 
 </div> #include &lt;pthread.h&gt;&nbsp; #include &lt;stdio.h&gt;&nbsp; #define NUM_THREADS&nbsp;&nbsp;&nbsp;&nbsp;3&nbsp; &nbsp; void *BusyWork(void *null)&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;int i;&nbsp; &nbsp;&nbsp;&nbsp;double result=0.0;&nbsp; &nbsp;&nbsp;&nbsp;for (i=0; i&lt;1000000; i++)&nbsp; &nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;result = result + (double)random();&nbsp; &nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;printf("result = %e\n",result);&nbsp; &nbsp;&nbsp;&nbsp;pthread_exit((void *) 0);&nbsp; }&nbsp; &nbsp; int main (int argc, char *argv[])&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;pthread_t thread[NUM_THREADS];&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_t attr;&nbsp; &nbsp;&nbsp;&nbsp;int rc, t;&nbsp; &nbsp; &nbsp;void *status;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;/* Initialize and set thread detached attribute */&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_init(&amp;attr);&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_setdetachstate(&amp;attr, PTHREAD_CREATE_JOINABLE);&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;for(t=0; t&lt;NUM_THREADS; t++)&nbsp; &nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("Creating thread %d\n", t);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rc = pthread_create(&amp;thread[t], &amp;attr, BusyWork, NULL);&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (rc)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("ERROR; return code from pthread_create() &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;is %d\n", rc);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exit(-1);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;}&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;/* Free attribute and wait for the other threads */&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_destroy(&amp;attr);&nbsp; &nbsp;&nbsp;&nbsp;for(t=0; t&lt;NUM_THREADS; t++)&nbsp; &nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rc = pthread_join(thread[t], &amp;status);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (rc)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("ERROR; return code from pthread_join() &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;is %d\n", rc);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exit(-1);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("Completed join with thread %d status= %ld\n",t, (long)status);&nbsp; &nbsp;&nbsp;&nbsp;}&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/join1.c" style="color:rgb(0,0,0)" rel="nofollow"></a><a href="https://computing.llnl.gov/tutorials/pthreads/samples/join1.out" style="color:rgb(0,0,0)" rel="nofollow"></a>&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**栈管理 **

**函数:**

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getstacksize.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getstacksize</a>&nbsp;(attr, stacksize) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setstacksize.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setstacksize</a>&nbsp;(attr, stacksize)&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getstackaddr.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getstackaddr</a>&nbsp;(attr, stackaddr) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setstackaddr.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setstackaddr</a>&nbsp;(attr, stackaddr)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**防止栈问题:**

*  POSIX标准并没有指定线程栈的大小，依赖于实现并随实现变化。 
 *  很容易超出默认的栈大小，常见结果：程序终止或者数据损坏。 
 *  安全和可移植的程序应该不依赖于默认的栈限制，但是取而代之的是用pthread\_attr\_setstacksize分配足够的栈大小。 
 *  pthread\_attr\_getstackaddr和pthread\_attr\_setstackaddr函数可以被程序用于将栈设置在指定的内存区域。

**在LC上的一些实际例子:**

*  默认栈大小经常变化很大，最大值也变化很大，可能会依赖于每个节点的线程数目。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Node Architecture&nbsp; </td> 
 <td> #CPUs&nbsp; </td> 
 <td> Memory (GB)&nbsp; </td> 
 <td> Default Size (bytes)&nbsp; </td> 
 </tr> 
 <tr> 
 <td> AMD Opteron&nbsp; </td> 
 <td> 8&nbsp; </td> 
 <td> 16&nbsp; </td> 
 <td> 2,097,152&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Intel IA64&nbsp; </td> 
 <td> 4&nbsp; </td> 
 <td> 8&nbsp; </td> 
 <td> 33,554,432&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Intel IA32&nbsp; </td> 
 <td> 2&nbsp; </td> 
 <td> 4&nbsp; </td> 
 <td> 2,097,152&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM Power5&nbsp; </td> 
 <td> 8&nbsp; </td> 
 <td> 32&nbsp; </td> 
 <td> 196,608&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM Power4&nbsp; </td> 
 <td> 8&nbsp; </td> 
 <td> 16&nbsp; </td> 
 <td> 196,608&nbsp; </td> 
 </tr> 
 <tr> 
 <td> IBM Power3&nbsp; </td> 
 <td> 16&nbsp; </td> 
 <td> 16&nbsp; </td> 
 <td> 98,304&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

--------------------

**例子: 栈管理 **

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example Code - Stack Management&nbsp;&nbsp; 这个例子演示了如何去查询和设定线程栈大小。&nbsp;&nbsp; 
 <div> 
 <hr> 
 </div> #include &lt;pthread.h&gt;&nbsp; #include &lt;stdio.h&gt;&nbsp; #define NTHREADS 4&nbsp; #define N 1000&nbsp; #define MEGEXTRA 1000000&nbsp; &nbsp;&nbsp; pthread_attr_t attr;&nbsp; &nbsp;&nbsp; void *dowork(void *threadid)&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;double A[N][N];&nbsp; &nbsp;&nbsp;&nbsp;int i,j,tid;&nbsp; &nbsp;&nbsp;&nbsp;size_t mystacksize;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;tid = (int)threadid;&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_getstacksize (&amp;attr, &amp;mystacksize);&nbsp; &nbsp;&nbsp;&nbsp;printf("Thread %d: stack size = %li bytes \n", tid, mystacksize);&nbsp; &nbsp;&nbsp;&nbsp;for (i=0; i&lt;N; i++)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for (j=0; j&lt;N; j++)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;A[i][j] = ((i*j)/3.452) + (N-i);&nbsp; &nbsp;&nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp; &nbsp;&nbsp; int main(int argc, char *argv[])&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;pthread_t threads[NTHREADS];&nbsp; &nbsp;&nbsp;&nbsp;size_t stacksize;&nbsp; &nbsp;&nbsp;&nbsp;int rc, t;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_init(&amp;attr);&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_getstacksize (&amp;attr, &amp;stacksize);&nbsp; &nbsp;&nbsp;&nbsp;printf("Default stack size = %li\n", stacksize);&nbsp; &nbsp;&nbsp;&nbsp;stacksize = sizeof(double)*N*N+MEGEXTRA;&nbsp; &nbsp;&nbsp;&nbsp;printf("Amount of stack needed per thread = %li\n",stacksize);&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_setstacksize (&amp;attr, stacksize);&nbsp; &nbsp;&nbsp;&nbsp;printf("Creating threads with stack size = %li bytes\n",stacksize);&nbsp; &nbsp;&nbsp;&nbsp;for(t=0; t&lt;NTHREADS; t++){&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rc =&nbsp;pthread_create(&amp;threads[t], &amp;attr, dowork, (void *)t);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (rc){&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("ERROR; return code from pthread_create() is %d\n", rc);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exit(-1);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;printf("Created %d threads.\n", t);&nbsp; &nbsp;&nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**其他各种函数： **

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_self.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_self</a>&nbsp;() &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_equal.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_equal</a>&nbsp;(thread1,thread2)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

*  pthread\_self返回调用该函数的线程的唯一，系统分配的线程ID。 
 *  pthread\_equal比较两个线程ID,若不同返回0，否则返回非0值。 
 *  注意这两个函数中的线程ID对象是不透明的，不是轻易能检查的。因为线程ID是不透明的对象，所以C语言的==操作符不能用于比较两个线程ID。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_once.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_once</a>&nbsp;(once_control, init_routine)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

*  pthread\_once 在一个进程中仅执行一次init\_routine。任何线程第一次调用该函数会执行给定的init\_routine，不带参数，任何后续调用都没有效果。 
 *  init\_routine函数一般是初始化的程序 
 *  once\_control参数是一个同步结构体，需要在调用pthread\_once前初始化。例如：

pthread\_once\_t once\_control = PTHREAD\_ONCE\_INIT;

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a rel="nofollow"></a>互斥量（Mutex Variables）&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**概述 **

*  互斥量（Mutex）是“mutual exclusion”的缩写。互斥量是实现线程同步，和保护同时写共享数据的主要方法 
 *  互斥量对共享数据的保护就像一把锁。在Pthreads中，任何时候仅有一个线程可以锁定互斥量，因此，当多个线程尝试去锁定该互斥量时仅有一个会成功。直到锁定互斥量的线程解锁互斥量后，其他线程才可以去锁定互斥量。线程必须轮着访问受保护数据。 
 *  互斥量可以防止“竞争”条件。下面的例子是一个银行事务处理时发生了竞争条件：

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Thread 1&nbsp; </td> 
 <td> Thread 2&nbsp; </td> 
 <td> Balance&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Read balance: $1000&nbsp; </td> 
 <td> &nbsp;&nbsp; </td> 
 <td> $1000&nbsp; </td> 
 </tr> 
 <tr> 
 <td> &nbsp;&nbsp; </td> 
 <td> Read balance: $1000&nbsp; </td> 
 <td> $1000&nbsp; </td> 
 </tr> 
 <tr> 
 <td> &nbsp;&nbsp; </td> 
 <td> Deposit $200&nbsp; </td> 
 <td> $1000&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Deposit $200&nbsp; </td> 
 <td> &nbsp;&nbsp; </td> 
 <td> $1000&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Update balance $1000+$200&nbsp; </td> 
 <td> &nbsp;&nbsp; </td> 
 <td> $1200&nbsp; </td> 
 </tr> 
 <tr> 
 <td> &nbsp;&nbsp; </td> 
 <td> Update balance $1000+$200&nbsp; </td> 
 <td> $1200&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

*  上面的例子，当一个线程使用共享数据资源时，应该用一个互斥量去锁定“Balance”。 
 *  一个拥有互斥量的线程经常用于更新全局变量。确保了多个线程更新同样的变量以安全的方式运行，最终的结果和一个线程处理的结果是相同的。这个更新的变量属于一个“临界区（critical section）”。 
 *  使用互斥量的典型顺序如下： 
    
     *  创建和初始一个互斥量 
     *  多个线程尝试去锁定该互斥量 
     *  仅有一个线程可以成功锁定改互斥量 
     *  锁定成功的线程做一些处理 
     *  线程解锁该互斥量 
     *  另外一个线程获得互斥量，重复上述过程 
     *  最后销毁互斥量 
 *  当多个线程竞争同一个互斥量时，失败的线程会阻塞在lock调用处。可以用“trylock”替换“lock”，则失败时不会阻塞。 
 *  当保护共享数据时，程序员有责任去确认是否需要使用互斥量。如，若四个线程会更新同样的数据，但仅有一个线程用了互斥量，则数据可能会损坏。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> 互斥量（Mutex Variables）&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**创建和销毁互斥量 **

**函数：**

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_init</a>&nbsp;(mutex,attr) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_destroy</a>&nbsp;(mutex)&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_init</a>&nbsp;(attr) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_destroy</a>&nbsp;(attr)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**用法：**

*  互斥量必须用类型pthread\_mutex\_t类型声明，在使用前必须初始化，这里有两种方法可以初始化互斥量： 
    
    1.  声明时静态地，如：  
        pthread\_mutex\_t mymutex = PTHREAD\_MUTEX\_INITIALIZER;  
    2.  动态地用pthread\_mutex\_init()函数，这种方法允许设定互斥量的属性对象attr。

互斥量初始化后是解锁的。

*  attr对象用于设置互斥量对象的属性，使用时必须声明为pthread\_mutextattr\_t类型，默认值可以是NULL。Pthreads标准定义了三种可选的互斥量属性：

*   
    
     *  协议（Protocol）： 指定了协议用于阻止互斥量的优先级改变 
     *  优先级上限（Prioceiling）：指定互斥量的优先级上限 
     *  进程共享（Process-shared）：指定进程共享互斥量

注意所有实现都提供了这三个可先的互斥量属性。

*  pthread\_mutexattr\_init()和pthread\_mutexattr\_destroy()函数分别用于创建和销毁互斥量属性对象。 
 *  pthread\_mutex\_destroy()应该用于释放不需要再使用的互斥量对象。

**锁定和解锁互斥量 **

**函数：**

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_lock.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_lock</a>&nbsp;(mutex) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_trylock.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_trylock</a>&nbsp;(mutex)&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_unlock.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_unlock</a>&nbsp;(mutex)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**用法：**

*  线程用pthread\_mutex\_lock()函数去锁定指定的mutex变量，若该mutex已经被另外一个线程锁定了，该调用将会阻塞线程直到mutex被解锁。 
 *  pthread\_mutex\_trylock() will attempt to lock a mutex. However, if the mutex is already locked, the routine will return immediately with a "busy" error code. This routine may be useful in  
 *  pthread\_mutex\_trylock()尝试着去锁定一个互斥量，然而，若互斥量已被锁定，程序会立刻返回并返回一个忙错误值。该函数在优先级改变情况下阻止死锁是非常有用的。 
 *  线程可以用pthread\_mutex\_unlock()解锁自己占用的互斥量。在一个线程完成对保护数据的使用，而其它线程要获得互斥量在保护数据上工作时，可以调用该函数。若有一下情形则会发生错误： 
    
     *  互斥量已经被解锁 
     *  互斥量被另一个线程占用 
 *  互斥量并没有多么“神奇”的，实际上，它们就是参与的线程的“君子约定”。写代码时要确信正确地锁定，解锁互斥量。下面演示了一种逻辑错误：

·                    **Thread 1     Thread 2     Thread 3**

·                    Lock         Lock

·                    A = 2        A = A+1      A = A\*B

·                    Unlock       Unlock

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> &nbsp; </td> 
 <td> &nbsp; </td> 
 <td> Q：有多个线程等待同一个锁定的互斥量，当互斥量被解锁后，那个线程会第一个锁定互斥量？&nbsp; A：除非线程使用了优先级调度机制，否则，线程会被系统调度器去分配，那个线程会第一个锁定互斥量是随机的。&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

--------------------

**例子：使用互斥量 **

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example Code - Using Mutexes&nbsp;&nbsp; 例程演示了线程使用互斥量处理一个点积（dot product）计算。主数据通过一个可全局访问的数据结构被所有线程使用，每个线程处理数据的不同部分，主线程等待其他线程完成计算并输出结果。&nbsp; 
 <div> 
 <hr> 
 </div> #include &lt;pthread.h&gt;&nbsp; #include &lt;stdio.h&gt;&nbsp; #include &lt;malloc.h&gt;&nbsp; &nbsp; /*&nbsp;&nbsp;&nbsp;&nbsp; The following structure contains the necessary information&nbsp;&nbsp;&nbsp; to allow the function "dotprod" to access its input data and &nbsp; place its output into the structure.&nbsp;&nbsp;&nbsp; */&nbsp; &nbsp; typedef struct &nbsp; &nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;double&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*a;&nbsp; &nbsp;&nbsp;&nbsp;double&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*b;&nbsp; &nbsp;&nbsp;&nbsp;double&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sum; &nbsp; &nbsp;&nbsp;&nbsp;int&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;veclen; &nbsp; &nbsp;} DOTDATA;&nbsp; &nbsp; /* Define globally accessible variables and a mutex */&nbsp; &nbsp; #define NUMTHRDS 4&nbsp; #define VECLEN 100&nbsp; &nbsp;&nbsp;&nbsp;DOTDATA dotstr; &nbsp; &nbsp;&nbsp;&nbsp;pthread_t callThd[NUMTHRDS];&nbsp; &nbsp;&nbsp;&nbsp;pthread_mutex_t mutexsum;&nbsp; &nbsp; /*&nbsp; The function dotprod is activated when the thread is created.&nbsp; All input to this routine is obtained from a structure &nbsp; of type DOTDATA and all output from this function is written into&nbsp; this structure. The benefit of this approach is apparent for the &nbsp; multi-threaded program: when a thread is created we pass a single&nbsp; argument to the activated function - typically this argument&nbsp; is a thread number. All&nbsp;&nbsp;the other information required by the &nbsp; function is accessed from the globally accessible structure. &nbsp; */&nbsp; &nbsp; void *dotprod(void *arg)&nbsp; {&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;/* Define and use local variables for convenience */&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;int i, start, end, offset, len ;&nbsp; &nbsp;&nbsp;&nbsp;double mysum, *x, *y;&nbsp; &nbsp;&nbsp;&nbsp;offset = (int)arg;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;len = dotstr.veclen;&nbsp; &nbsp;&nbsp;&nbsp;start = offset*len;&nbsp; &nbsp;&nbsp;&nbsp;end&nbsp;&nbsp;&nbsp;= start + len;&nbsp; &nbsp;&nbsp;&nbsp;x = dotstr.a;&nbsp; &nbsp;&nbsp;&nbsp;y = dotstr.b;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;/*&nbsp; &nbsp;&nbsp;&nbsp;Perform the dot product and assign result&nbsp; &nbsp;&nbsp;&nbsp;to the appropriate variable in the structure. &nbsp; &nbsp;&nbsp;&nbsp;*/&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;mysum = 0;&nbsp; &nbsp;&nbsp;&nbsp;for (i=start; i&lt;end ; i++) &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;mysum += (x[i] * y[i]);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;/*&nbsp; &nbsp;&nbsp;&nbsp;Lock a mutex prior to updating the value in the shared&nbsp; &nbsp;&nbsp;&nbsp;structure, and unlock it upon updating.&nbsp; &nbsp;&nbsp;&nbsp;*/&nbsp; &nbsp;&nbsp;&nbsp;pthread_mutex_lock (&amp;mutexsum);&nbsp; &nbsp;&nbsp;&nbsp;dotstr.sum += mysum;&nbsp; &nbsp;&nbsp;&nbsp;pthread_mutex_unlock (&amp;mutexsum);&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;pthread_exit((void*) 0);&nbsp; }&nbsp; &nbsp; /* &nbsp; The main program creates threads which do all the work and then &nbsp; print out result upon completion. Before creating the threads,&nbsp; the input data is created. Since all threads update a shared structure, &nbsp; we need a mutex for mutual exclusion. The main thread needs to wait for&nbsp; all threads to complete, it waits for each one of the threads. We specify&nbsp; a thread attribute value that allow the main thread to join with the&nbsp; threads it creates. Note also that we free up handles when they are&nbsp; no longer needed.&nbsp; */&nbsp; &nbsp; int main (int argc, char *argv[])&nbsp; {&nbsp; &nbsp;&nbsp;&nbsp;int i;&nbsp; &nbsp;&nbsp;&nbsp;double *a, *b;&nbsp; &nbsp;&nbsp;&nbsp;void *status;&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_t attr;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;/* Assign storage and initialize values */&nbsp; &nbsp;&nbsp;&nbsp;a = (double*) malloc (NUMTHRDS*VECLEN*sizeof(double));&nbsp; &nbsp;&nbsp;&nbsp;b = (double*) malloc (NUMTHRDS*VECLEN*sizeof(double));&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;for (i=0; i&lt;VECLEN*NUMTHRDS; i++)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a[i]=1.0;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b[i]=a[i];&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;dotstr.veclen = VECLEN; &nbsp; &nbsp;&nbsp;&nbsp;dotstr.a = a; &nbsp; &nbsp;&nbsp;&nbsp;dotstr.b = b; &nbsp; &nbsp;&nbsp;&nbsp;dotstr.sum=0;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;pthread_mutex_init(&amp;mutexsum, NULL);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;/* Create threads to perform the dotproduct&nbsp;&nbsp;*/&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_init(&amp;attr);&nbsp; &nbsp;&nbsp;&nbsp;pthread_attr_setdetachstate(&amp;attr, PTHREAD_CREATE_JOINABLE);&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for(i=0; i&lt;NUMTHRDS; i++)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/* &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Each thread works on a different set of data.&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The offset is specified by 'i'. The size of&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;the data for each thread is indicated by VECLEN.&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*/&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pthread_create( &amp;callThd[i], &amp;attr, dotprod, (void *)i);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pthread_attr_destroy(&amp;attr);&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/* Wait on the other threads */&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for(i=0; i&lt;NUMTHRDS; i++)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;{&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;pthread_join( callThd[i], &amp;status);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;/* After joining, print out the results and cleanup */&nbsp; &nbsp;&nbsp;&nbsp;printf ("Sum =&nbsp;&nbsp;%f \n", dotstr.sum);&nbsp; &nbsp;&nbsp;&nbsp;free (a);&nbsp; &nbsp;&nbsp;&nbsp;free (b);&nbsp; &nbsp;&nbsp;&nbsp;pthread_mutex_destroy(&amp;mutexsum);&nbsp; &nbsp;&nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp;&nbsp;&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/dotprod_serial.c" style="color:rgb(0,0,0)" rel="nofollow"></a>Serial version&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/dotprod_mutex.c" style="color:rgb(0,0,0)" rel="nofollow"></a>Pthreads version&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a rel="nofollow"></a>条件变量（Condition Variables）&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**概述 **

*  条件变量提供了另一种同步的方式。互斥量通过控制对数据的访问实现了同步，而条件变量允许根据实际的数据值来实现同步。 
 *  没有条件变量，程序员就必须使用线程去轮询（可能在临界区），查看条件是否满足。这样比较消耗资源，因为线程连续繁忙工作。条件变量是一种可以实现这种轮询的方式。 
 *  条件变量往往和互斥一起使用 
 *  使用条件变量的代表性顺序如下：

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td colspan="2"> 主线程（Main Thread）&nbsp;&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;声明和初始化需要同步的全局数据/变量（如“count”）&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;生命和初始化一个条件变量对象&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;声明和初始化一个相关的互斥量&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;创建工作线程A和B&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Thread A&nbsp;&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;工作，一直到一定的条件满足（如“count”等于一个指定的值）&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;锁定相关互斥量并检查全局变量的值&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;调用pthread_cond_wait()阻塞等待Thread-B的信号。注意pthread_cond_wait()能够自动地并且原子地解锁相关的互斥量，以至于它可以被Thread-B使用。&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;当收到信号，唤醒线程，互斥量被自动，原子地锁定。&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;显式解锁互斥量&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;继续&nbsp; </td> 
 <td> Thread B&nbsp;&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;工作&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;锁定相关互斥量&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;改变Thread-A所等待的全局变量&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;检查全局变量的值，若达到需要的条件，像Thread-A发信号。&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;解锁互斥量&nbsp; o&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;继续&nbsp; </td> 
 </tr> 
 <tr> 
 <td colspan="2"> Main Thread&nbsp;&nbsp; Join / Continue &nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> 条件变量（Condition Variables）&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**创建和销毁条件变量 **

**Routines:**

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_init</a>&nbsp;(condition,attr) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_destroy</a>&nbsp;(condition)&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_condattr_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_condattr_init</a>&nbsp;(attr) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_condattr_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_condattr_destroy</a>&nbsp;(attr)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**Usage:**

*  条件变量必须声明为pthread\_cond\_t类型，必须在使用前初始化。有两种方式可以初始条件变量： 
    
    1.  声明时静态地。如：  
        pthread\_cond\_t myconvar = PTHREAD\_COND\_INITIALIZER;  
    2.  用pthread\_cond\_init()函数动态地。创建的条件变量ID通过condition参数返回给调用线程。该方式允许设置条件变量对象的属性，attr。 
 *   
 *  可选的attr对象用于设定条件变量的属性。仅有一个属性被定义：线程共享（process-shared），可以使条件变量被其它进程中的线程看到。若要使用属性对象，必须定义为pthread\_condattr\_t类型（可以指定为NULL设为默认）。

注意所有实现都提供了线程共享属性。

*  pthread\_condattr\_init()和pthread\_condattr\_destroy()用于创建和销毁条件变量属性对象。 
 *  条件变量不需要再使用时，应用pthread\_cond\_destroy()释放条件变量。

**在条件变量上等待（Waiting）和发送信号（Signaling） **

**函数：**

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_wait.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_wait</a>&nbsp;(condition,mutex) &nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_signal.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_signal</a>&nbsp;(condition)&nbsp;&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_broadcast.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_broadcast</a>&nbsp;(condition)&nbsp;&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

**用法：**

*  pthread\_cond\_wait()阻塞调用线程直到指定的条件受信（signaled）。该函数应该在互斥量锁定时调用，当在等待时会自动解锁互斥量。在信号被发送，线程被激活后，互斥量会自动被锁定，当线程结束时，由程序员负责解锁互斥量。 
 *  pthread\_cond\_signal()函数用于向其他等待在条件变量上的线程发送信号（激活其它线程）。应该在互斥量被锁定后调用。 
 *  若不止一个线程阻塞在条件变量上，则应用pthread\_cond\_broadcast()向其它所以线程发生信号。 
 *  在调用pthread\_cond\_wait()前调用pthread\_cond\_signal()会发生逻辑错误。

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> &nbsp; </td> 
 <td> 使用这些函数时适当的锁定和解锁相关的互斥量是非常重要的。如：&nbsp; 
 <ul> 
 <li>调用pthread_cond_wait()前锁定互斥量失败可能导致线程不会阻塞。&nbsp;</li> 
 <li>调用pthread_cond_signal()后解锁互斥量失败可能会不允许相应的pthread_cond_wait()函数结束（保存阻塞）。&nbsp;</li> 
 </ul> </td> 
 </tr> 
 </tbody> 
</table>

--------------------

**例子：使用条件变量 **

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> Example Code - Using Condition Variables&nbsp;&nbsp; 例子演示了使用Pthreads条件变量的几个函数。主程序创建了三个线程，两个线程工作，根系“count”变量。第三个线程等待count变量值达到指定的值。&nbsp; 
 <div> 
 <hr> 
 </div> #include &lt;pthread.h&gt;&nbsp; #include &lt;stdio.h&gt;&nbsp; &nbsp; #define NUM_THREADS&nbsp;&nbsp;3&nbsp; #define TCOUNT 10&nbsp; #define COUNT_LIMIT 12&nbsp; &nbsp; int&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;count = 0;&nbsp; int&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;thread_ids[3] = {0,1,2};&nbsp; pthread_mutex_t count_mutex;&nbsp; pthread_cond_t count_threshold_cv;&nbsp; &nbsp; void *inc_count(void *idp) &nbsp; {&nbsp; &nbsp;&nbsp;int j,i;&nbsp; &nbsp;&nbsp;double result=0.0;&nbsp; &nbsp;&nbsp;int *my_id = idp;&nbsp; &nbsp; &nbsp;&nbsp;for (i=0; i&lt;TCOUNT; i++) {&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;pthread_mutex_lock(&amp;count_mutex);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;count++;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;/* &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;Check the value of count and signal waiting thread when condition is&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;reached.&nbsp;&nbsp;Note that this occurs while mutex is locked. &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;*/&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;if (count == COUNT_LIMIT) {&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pthread_cond_signal(&amp;count_threshold_cv);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("inc_count(): thread %d, count = %d&nbsp;&nbsp;Threshold reached.\n", &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*my_id, count);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;printf("inc_count(): thread %d, count = %d, unlocking mutex\n", &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;*my_id, count);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;pthread_mutex_unlock(&amp;count_mutex);&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;/* Do some work so threads can alternate on mutex lock */&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;for (j=0; j&lt;1000; j++)&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;result = result + (double)random();&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp; &nbsp; void *watch_count(void *idp) &nbsp; {&nbsp; &nbsp;&nbsp;int *my_id = idp;&nbsp; &nbsp; &nbsp;&nbsp;printf("Starting watch_count(): thread %d\n", *my_id);&nbsp; &nbsp; &nbsp;&nbsp;/*&nbsp; &nbsp;&nbsp;Lock mutex and wait for signal.&nbsp;&nbsp;Note that the pthread_cond_wait &nbsp; &nbsp;&nbsp;routine will automatically and atomically unlock mutex while it waits. &nbsp; &nbsp;&nbsp;Also, note that if COUNT_LIMIT is reached before this routine is run by&nbsp; &nbsp;&nbsp;the waiting thread, the loop will be skipped to prevent pthread_cond_wait&nbsp; &nbsp;&nbsp;from never returning. &nbsp; &nbsp;&nbsp;*/&nbsp; &nbsp;&nbsp;pthread_mutex_lock(&amp;count_mutex);&nbsp; &nbsp;&nbsp;if (count&lt;COUNT_LIMIT) {&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;pthread_cond_wait(&amp;count_threshold_cv, &amp;count_mutex);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;printf("watch_count(): thread %d Condition signal &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;received.\n", *my_id);&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;pthread_mutex_unlock(&amp;count_mutex);&nbsp; &nbsp;&nbsp;pthread_exit(NULL);&nbsp; }&nbsp; &nbsp; int main (int argc, char *argv[])&nbsp; {&nbsp; &nbsp;&nbsp;int i, rc;&nbsp; &nbsp;&nbsp;pthread_t threads[3];&nbsp; &nbsp;&nbsp;pthread_attr_t attr;&nbsp; &nbsp; &nbsp;&nbsp;/* Initialize mutex and condition variable objects */&nbsp; &nbsp;&nbsp;pthread_mutex_init(&amp;count_mutex, NULL);&nbsp; &nbsp;&nbsp;pthread_cond_init (&amp;count_threshold_cv, NULL);&nbsp; &nbsp; &nbsp;&nbsp;/* For portability, explicitly create threads in a joinable state */&nbsp; &nbsp;&nbsp;pthread_attr_init(&amp;attr);&nbsp; &nbsp;&nbsp;pthread_attr_setdetachstate(&amp;attr, PTHREAD_CREATE_JOINABLE);&nbsp; &nbsp;&nbsp;pthread_create(&amp;threads[0], &amp;attr, inc_count, (void *)&amp;thread_ids[0]);&nbsp; &nbsp;&nbsp;pthread_create(&amp;threads[1], &amp;attr, inc_count, (void *)&amp;thread_ids[1]);&nbsp; &nbsp;&nbsp;pthread_create(&amp;threads[2], &amp;attr, watch_count, (void *)&amp;thread_ids[2]);&nbsp; &nbsp; &nbsp;&nbsp;/* Wait for all threads to complete */&nbsp; &nbsp;&nbsp;for (i=0; i&lt;NUM_THREADS; i++) {&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;pthread_join(threads[i], NULL);&nbsp; &nbsp;&nbsp;}&nbsp; &nbsp;&nbsp;printf ("Main(): Waited on %d&nbsp;&nbsp;threads. Done.\n", NUM_THREADS);&nbsp; &nbsp; &nbsp;&nbsp;/* Clean up and exit */&nbsp; &nbsp;&nbsp;pthread_attr_destroy(&amp;attr);&nbsp; &nbsp;&nbsp;pthread_mutex_destroy(&amp;count_mutex);&nbsp; &nbsp;&nbsp;pthread_cond_destroy(&amp;count_threshold_cv);&nbsp; &nbsp;&nbsp;pthread_exit(NULL);&nbsp; &nbsp; }&nbsp; <a href="https://computing.llnl.gov/tutorials/pthreads/samples/condvar1.c" style="color:rgb(0,0,0)" rel="nofollow"></a><a href="https://computing.llnl.gov/tutorials/pthreads/samples/condvar1.out" style="color:rgb(0,0,0)" rel="nofollow"></a>&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a rel="nofollow"></a>没有覆盖的主题&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

Pthread API的几个特性在该教程中并没有包含。把它们列在下面：

*  线程调度 
    
     *  线程如何调度的实现往往是不同的，在大多数情况下，默认的机制是可以胜任的。 
     *  Pthreads　API提供了显式设定线程调度策略和优先级的函数，它们可以重载默认机制。 
     *  API不需要实现去支持这些特性 
 *  Keys：线程数据（TSD） 
 *  互斥量的Protocol属性和优先级管理 
 *  跨进程的条件变量共享 
 *  Thread Cancellation  
 *  取消线程（Thread Cancellation ） 
 *  多线程和信号（Threads and Signals）

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td> <a rel="nofollow"></a>Pthread&nbsp;库API参考&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

<table style="color:rgb(51,51,51)"> 
 <tbody> 
 <tr> 
 <td colspan="2"> Pthread Functions&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Thread Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_create.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_create</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_exit.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_exit</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_join.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_join</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_once.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_once</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_kill.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_kill</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_self.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_self</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_equal.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_equal</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_yield.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_yield</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_detach.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_detach</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Thread-Specific Data&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_key_create.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_key_create&nbsp;</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_key_delete.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_key_delete</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_getspecific.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_getspecific&nbsp;</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_setspecific.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_setspecific</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Thread Cancellation&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cancel.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cancel</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cleanup_pop.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cleanup_pop</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cleanup_push.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cleanup_push</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_setcancelstate.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_setcancelstate</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> pthread_getcancelstate &nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_testcancel.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_testcancel</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Thread Scheduling&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_getschedparam.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_getschedparam</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_setschedparam.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_setschedparam</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Signals&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_sigmask.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_sigmask</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td colspan="2"> Pthread Attribute Functions&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Basic Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_init</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_destroy</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Detachable or Joinable&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setdetachstate.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setdetachstate</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getdetachstate.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getdetachstate</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Specifying Stack Information&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getstackaddr.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getstackaddr</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getstacksize.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getstacksize</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setstackaddr.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setstackaddr</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setstacksize.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setstacksize</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Thread Scheduling Attributes&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getschedparam.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getschedparam</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setschedparam.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setschedparam</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getschedpolicy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getschedpolicy</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setschedpolicy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setschedpolicy</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setinheritsched.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setinheritsched</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getinheritsched.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getinheritsched</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_setscope.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_setscope</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_attr_getscope.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_attr_getscope</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td colspan="2"> Mutex Functions&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Mutex Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_init</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_destroy</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_lock.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_lock</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_unlock.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_unlock</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_trylock.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_trylock</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Priority Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_setprioceiling.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_setprioceiling</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutex_getprioceiling.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutex_getprioceiling</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td colspan="2"> Mutex Attribute Functions&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Basic Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_init</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_destroy</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Sharing&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_getpshared.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_getpshared</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_setpshared.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_setpshared</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Protocol Attributes&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_getprotocol.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_getprotocol</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_setprotocol.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_setprotocol</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Priority Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_setprioceiling.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_setprioceiling</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_mutexattr_getprioceiling.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_mutexattr_getprioceiling</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td colspan="2"> Condition Variable Functions&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Basic Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_init</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_destroy</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_signal.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_signal</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_broadcast.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_broadcast</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_wait.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_wait</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_cond_timedwait.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_cond_timedwait</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td colspan="2"> Condition Variable Attribute Functions&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Basic Management&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_condattr_init.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_condattr_init</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_condattr_destroy.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_condattr_destroy</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> Sharing&nbsp; </td> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_condattr_getpshared.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_condattr_getpshared</a>&nbsp; </td> 
 </tr> 
 <tr> 
 <td> <a href="https://computing.llnl.gov/tutorials/pthreads/man/pthread_condattr_setpshared.txt" style="color:rgb(0,0,0)" rel="nofollow">pthread_condattr_setpshared</a>&nbsp; </td> 
 </tr> 
 </tbody> 
</table>

--------------------

*  Author: [Blaise Barney][], Livermore Computing.  
 *  "Pthreads Programming". B. Nichols et al. O'Reilly and Associates.  
 *  "Threads Primer". B. Lewis and D. Berg. Prentice Hall  
 *  "Programming With POSIX Threads". D. Butenhof. Addison Wesley   
    [www.awl.com/cseng/titles/0-201-63392-2][www.awl.com_cseng_titles_0-201-63392-2]  
 *  "Programming With Threads". S. Kleiman et al. Prentice Hall

--------------------

三天时间，终于在工作期间，抽空把上一篇POSIX threads programing翻译完了。由于水平有限，翻译质量差强人意，若有不合理或错误之处，请您之处，在此深表感谢！有疑问点此查看原文。在参考部分提及的几本关于Pthreads库的大作及该文章原文和译文可在下面的连接下载：

1.  本篇及其英文原文:   [http://download.csdn.net/source/992256][http_download.csdn.net_source_992256]
2.  多线程编程指南:   [http://download.csdn.net/source/992248][http_download.csdn.net_source_992248]
3.  Programing with POSIX thread(强烈推荐):  [http://download.csdn.net/source/992239][http_download.csdn.net_source_992239]
4.  Pthread Primer(强烈推荐):  [http://download.csdn.net/source/992213][http_download.csdn.net_source_992213]

author: david([Heaven.Hell.Or@gmail.com][Heaven.Hell.Or_gmail.com])  
code page:[http://code.google.com/p/heavenhell/][http_code.google.com_p_heavenhell]

[http_download.csdn.net_detail_xiaoyao333000_6994423]: http://download.csdn.net/detail/xiaoyao333000/6994423
[Link 1]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#abstract
[Link 2]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#translator
[Pthreads]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#pthreads_overview
[Link 3]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#what_is_thread
[Pthreads_]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#what_is_pthreads
[Pthreads 1]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#why_pthreads
[Link 4]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#progrming_threads
[Pthreads API]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#Compiling
[Link 5]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#thread_management
[Link 6]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#create_terminate_thread
[Link 7]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#pass_param
[Joining_ Detaching_]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#join_detach
[Link 8]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#stack_management
[Link 9]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#micelleous_api
[Mutex Variables]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#mutex
[Link 10]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#mutex_overview
[Link 11]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#mutex_create_terminate
[Locking_Unlocking]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#mutex_lock_unlock
[Condition Variable]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#ConVarOverview
[Link 12]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#condition_overview
[Link 13]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#condition_create_terminate
[Waiting_Signaling]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#waiting_signaling
[Link 14]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#topic_not_covered
[Pthread _API]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#phtread_ref
[Link 15]: http://www.cnblogs.com/mywolrd/archive/2009/02/05/1930707.html#ref
[EC3500_ Introduction To Parallel Computing]: https://computing.llnl.gov/tutorials/parallel_comp
[fork_vs_thread.txt]: https://computing.llnl.gov/tutorials/pthreads/fork_vs_thread.txt
[Blaise Barney]: mailto:blaiseb@llnl.gov
[www.awl.com_cseng_titles_0-201-63392-2]: http://www.awl.com/cseng/titles/0-201-63392-2
[http_download.csdn.net_source_992256]: http://download.csdn.net/source/992256
[http_download.csdn.net_source_992248]: http://download.csdn.net/source/992248
[http_download.csdn.net_source_992239]: http://download.csdn.net/source/992239
[http_download.csdn.net_source_992213]: http://download.csdn.net/source/992213
[Heaven.Hell.Or_gmail.com]: mailto:Heaven.Hell.Or@gmail.com
[http_code.google.com_p_heavenhell]: http://code.google.com/p/heavenhell/