线程属性pthread_attr_t简介

本文编辑整理自： 

http://hi.baidu.com/7828058/blog/item/256e16decd1a385e94ee3784.html

http://www.ibm.com/developerworks/cn/linux/thread/posix_threadapi/part1/ 

  Posix线程中的线程属性pthread_attr_t主要包括scope属性、detach属性、堆栈地址、堆栈大小、优先级。在pthread_create中，把第二个参数设置为NULL的话，将采用默认的属性配置。

pthread_attr_t的主要属性的意义如下：

__detachstate，表示新线程是否与进程中其他线程脱离同步， 如果设置为PTHREAD_CREATE_DETACHED 则新线程不能用pthread_join()来同步，且在退出时自行释放所占用的资源。缺省为PTHREAD_CREATE_JOINABLE状态。这个属性也可以在线程创建并运行以后用pthread_detach()来设置，而一旦设置为PTHREAD_CREATE_DETACH状态（不论是创建时设置还是运行时设置）则不能再恢复到PTHREAD_CREATE_JOINABLE状态。

__schedpolicy，表示新线程的调度策略，主要包括SCHED_OTHER（正常、非实时）、SCHED_RR（实时、轮转法）和SCHED_FIFO（实时、先入先出）三种，缺省为SCHED_OTHER，后两种调度策略仅对超级用户有效。运行时可以用过pthread_setschedparam()来改变。

__schedparam，一个struct sched_param结构，目前仅有一个sched_priority整型变量表示线程的运行优先级。这个参数仅当调度策略为实时（即SCHED_RR或SCHED_FIFO）时才有效，并可以在运行时通过pthread_setschedparam()函数来改变，缺省为0。

__inheritsched，有两种值可供选择：PTHREAD_EXPLICIT_SCHED和PTHREAD_INHERIT_SCHED，前者表示新线程使用显式指定调度策略和调度参数（即attr中的值），而后者表示继承调用者线程的值。缺省为PTHREAD_EXPLICIT_SCHED。

__scope，表示线程间竞争CPU的范围，也就是说线程优先级的有效范围。POSIX的标准中定义了两个值：PTHREAD_SCOPE_SYSTEM和PTHREAD_SCOPE_PROCESS，前者表示与系统中所有线程一起竞争CPU时间，后者表示仅与同进程中的线程竞争CPU。目前LinuxThreads仅实现了PTHREAD_SCOPE_SYSTEM一值。

  为了设置这些属性，POSIX定义了一系列属性设置函数，包括pthread_attr_init()、pthread_attr_destroy()和与各个属性相关的pthread_attr_getXXX/pthread_attr_setXXX函数。

在设置线程属性 pthread_attr_t 之前，通常先调用pthread_attr_init来初始化，之后来调用相应的属性设置函数。

主要的函数如下：

1、pthread_attr_init

功能：        对线程属性变量的初始化。

头文件：     <pthread.h>

函数原型：   int pthread_attr_init (pthread_attr_t* attr);

函数传入值：attr:线程属性。

函数返回值：成功： 0

                失败： -1

2、pthread_attr_setscope

功能：        设置线程 __scope 属性。scope属性表示线程间竞争CPU的范围，也就是说线程优先级的有效范围。POSIX的标准中定义了两个值：PTHREAD_SCOPE_SYSTEM和PTHREAD_SCOPE_PROCESS，前者表示与系统中所有线程一起竞争CPU时间，后者表示仅与同进程中的线程竞争CPU。默认为PTHREAD_SCOPE_PROCESS。目前LinuxThreads仅实现了PTHREAD_SCOPE_SYSTEM一值。

头文件：     <pthread.h>

函数原型：   int pthread_attr_setscope (pthread_attr_t* attr, int scope);

函数传入值：attr: 线程属性。

                      scope:PTHREAD_SCOPE_SYSTEM，表示与系统中所有线程一起竞争CPU时间，

                                 PTHREAD_SCOPE_PROCESS，表示仅与同进程中的线程竞争CPU

函数返回值得：同1。

3、pthread_attr_setdetachstate

功能：        设置线程detachstate属性。该表示新线程是否与进程中其他线程脱离同步，如果设置为PTHREAD_CREATE_DETACHED则新线程不能用pthread_join()来同步，且在退出时自行释放所占用的资源。缺省为PTHREAD_CREATE_JOINABLE状态。这个属性也可以在线程创建并运行以后用pthread_detach()来设置，而一旦设置为PTHREAD_CREATE_DETACH状态（不论是创建时设置还是运行时设置）则不能再恢复到PTHREAD_CREATE_JOINABLE状态。

头文件：      <phread.h>

函数原型：    int pthread_attr_setdetachstate (pthread_attr_t* attr, int detachstate);

函数传入值：attr:线程属性。

detachstate:PTHREAD_CREATE_DETACHED，不能用pthread_join()来同步，且在退出时自行释放所占用的资源

                    PTHREAD_CREATE_JOINABLE，能用pthread_join()来同步

函数返回值得：同1。

4、pthread_attr_setschedparam

功能：       设置线程schedparam属性，即调用的优先级。

头文件：     <pthread.h>

函数原型：   int pthread_attr_setschedparam (pthread_attr_t* attr, struct sched_param* param);

函数传入值：attr：线程属性。

                 param：线程优先级。一个struct sched_param结构，目前仅有一个sched_priority整型变量表示线程的运行优先级。这个参数仅当调度策略为实时（即SCHED_RR或SCHED_FIFO）时才有效，并可以在运行时通过pthread_setschedparam()函数来改变，缺省为0

函数返回值：同1。

5、pthread_attr_getschedparam

功能：       得到线程优先级。

头文件：    <pthread.h>

函数原型：  int pthread_attr_getschedparam (pthread_attr_t* attr, struct sched_param* param);

函数传入值：attr：线程属性；

                    param：线程优先级；

函数返回值：同1。

示例1：

<p style="PADDING-BOTTOM: 0px; MARGIN-TOP: 0px; MARGIN-BOTTOM: 10px; PADDING-TOP: 0px"></p><div><span class="com" style="color:#8800;">#include</span><span class="pln"> </span><span class="str" style="color:#0880;"><stdlib.h></span><span class="pln">   </span></div><div><span class="com" style="color:#8800;">#include</span><span class="pln"> </span><span class="str" style="color:#0880;"><stdio.h></span><span class="pln">   </span></div><div><span class="com" style="color:#8800;">#include</span><span class="pln"> </span><span class="str" style="color:#0880;"><errno.h></span><span class="pln">   </span></div><div><span class="com" style="color:#8800;">#include</span><span class="pln"> </span><span class="str" style="color:#0880;"><pthread.h></span><span class="pln">   </span></div><div></div><div><span class="kwd" style="color:#0088;">static</span><span class="pln"> </span><span class="kwd" style="color:#0088;">void</span><span class="pln"> pthread_func_1 </span><span class="pun" style="color:#66660;">(</span><span class="kwd" style="color:#0088;">void</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="kwd" style="color:#0088;">static</span><span class="pln"> </span><span class="kwd" style="color:#0088;">void</span><span class="pln"> pthread_func_2 </span><span class="pun" style="color:#66660;">(</span><span class="kwd" style="color:#0088;">void</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="kwd" style="color:#0088;">int</span><span class="pln"> main </span><span class="pun" style="color:#66660;">(</span><span class="kwd" style="color:#0088;">int</span><span class="pln"> argc</span><span class="pun" style="color:#66660;">,</span><span class="pln"> </span><span class="kwd" style="color:#0088;">char</span><span class="pun" style="color:#66660;">**</span><span class="pln"> argv</span><span class="pun" style="color:#66660;">)</span><span class="pln">   </span></div><div><span class="pun" style="color:#66660;">{</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="typ" style="color:#66066;">pthread_t</span><span class="pln"> pt_1 </span><span class="pun" style="color:#66660;">=</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="typ" style="color:#66066;">pthread_t</span><span class="pln"> pt_2 </span><span class="pun" style="color:#66660;">=</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="typ" style="color:#66066;">pthread_attr_t</span><span class="pln"> atrr </span><span class="pun" style="color:#66660;">=</span><span class="pln"> </span><span class="pun" style="color:#66660;">{</span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">};</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">int</span><span class="pln"> ret </span><span class="pun" style="color:#66660;">=</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pln">  </span></div><span style="LINE-HEIGHT: 22px"><span style="LINE-HEIGHT: 25px" class="pln">  </span><span class="com" style="color:#8800;LINE-HEIGHT: 25px">/*初始化属性线程属性*/</span></span><div><span class="pln">  pthread_attr_init </span><span class="pun" style="color:#66660;">(&</span><span class="pln">attr</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  pthread_attr_setscope </span><span class="pun" style="color:#66660;">(&</span><span class="pln">attr</span><span class="pun" style="color:#66660;">,</span><span class="pln"> PTHREAD_SCOPE_SYSTEM</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  pthread_attr_setdetachstate </span><span class="pun" style="color:#66660;">(&</span><span class="pln">attr</span><span class="pun" style="color:#66660;">,</span><span class="pln"> PTHREAD_CREATE_DETACHED</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">     </span></div><div><span class="pln">  ret </span><span class="pun" style="color:#66660;">=</span><span class="pln"> pthread_create </span><span class="pun" style="color:#66660;">(&</span><span class="pln">pt_1</span><span class="pun" style="color:#66660;">,</span><span class="pln"> </span><span class="pun" style="color:#66660;">&</span><span class="pln">attr</span><span class="pun" style="color:#66660;">,</span><span class="pln"> pthread_func_1</span><span class="pun" style="color:#66660;">,</span><span class="pln"> NULL</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">if</span><span class="pln"> </span><span class="pun" style="color:#66660;">(</span><span class="pln">ret </span><span class="pun" style="color:#66660;">!=</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">)</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">{</span><span class="pln">   </span></div><div><span class="pln">    perror </span><span class="pun" style="color:#66660;">(</span><span class="str" style="color:#0880;">"pthread_1_create"</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">}</span><span class="pln">   </span></div><div><span class="pln">     </span></div><div><span class="pln">  ret </span><span class="pun" style="color:#66660;">=</span><span class="pln"> pthread_create </span><span class="pun" style="color:#66660;">(&</span><span class="pln">pt_2</span><span class="pun" style="color:#66660;">,</span><span class="pln"> NULL</span><span class="pun" style="color:#66660;">,</span><span class="pln"> pthread_func_2</span><span class="pun" style="color:#66660;">,</span><span class="pln"> NULL</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">if</span><span class="pln"> </span><span class="pun" style="color:#66660;">(</span><span class="pln">ret </span><span class="pun" style="color:#66660;">!=</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">)</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">{</span><span class="pln">   </span></div><div><span class="pln">    perror </span><span class="pun" style="color:#66660;">(</span><span class="str" style="color:#0880;">"pthread_2_create"</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">}</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="pln">  pthread_join </span><span class="pun" style="color:#66660;">(</span><span class="pln">pt_2</span><span class="pun" style="color:#66660;">,</span><span class="pln"> NULL</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">return</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pun" style="color:#66660;">}</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="kwd" style="color:#0088;">static</span><span class="pln"> </span><span class="kwd" style="color:#0088;">void</span><span class="pln"> pthread_func_1 </span><span class="pun" style="color:#66660;">(</span><span class="kwd" style="color:#0088;">void</span><span class="pun" style="color:#66660;">)</span><span class="pln">   </span></div><div><span class="pun" style="color:#66660;">{</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">int</span><span class="pln"> i </span><span class="pun" style="color:#66660;">=</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pln">     </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">for</span><span class="pln"> </span><span class="pun" style="color:#66660;">(;</span><span class="pln"> i </span><span class="pun" style="color:#66660;"><</span><span class="pln"> </span><span class="lit" style="color:#06666;">6</span><span class="pun" style="color:#66660;">;</span><span class="pln"> i</span><span class="pun" style="color:#66660;">++)</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">{</span><span class="pln">    </span></div><div><span class="pln">    printf </span><span class="pun" style="color:#66660;">(</span><span class="str" style="color:#0880;">"This is pthread_1.\n"</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">      </span></div><div><span class="pln">    </span><span class="kwd" style="color:#0088;">if</span><span class="pln"> </span><span class="pun" style="color:#66660;">(</span><span class="pln">i </span><span class="pun" style="color:#66660;">==</span><span class="pln"> </span><span class="lit" style="color:#06666;">2</span><span class="pun" style="color:#66660;">)</span><span class="pln">   </span></div><div><span class="pln">    </span><span class="pun" style="color:#66660;">{</span><span class="pln">   </span></div><div><span class="pln">      pthread_exit </span><span class="pun" style="color:#66660;">(</span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">    </span><span class="pun" style="color:#66660;">}</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">}</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">return</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pun" style="color:#66660;">}</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="kwd" style="color:#0088;">static</span><span class="pln"> </span><span class="kwd" style="color:#0088;">void</span><span class="pln"> pthread_func_2 </span><span class="pun" style="color:#66660;">(</span><span class="kwd" style="color:#0088;">void</span><span class="pun" style="color:#66660;">)</span><span class="pln">   </span></div><div><span class="pun" style="color:#66660;">{</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">int</span><span class="pln"> i </span><span class="pun" style="color:#66660;">=</span><span class="pln"> </span><span class="lit" style="color:#06666;">0</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">for</span><span class="pln"> </span><span class="pun" style="color:#66660;">(;</span><span class="pln"> i </span><span class="pun" style="color:#66660;"><</span><span class="pln"> </span><span class="lit" style="color:#06666;">3</span><span class="pun" style="color:#66660;">;</span><span class="pln"> i </span><span class="pun" style="color:#66660;">++)</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">{</span><span class="pln">   </span></div><div><span class="pln">    printf </span><span class="pun" style="color:#66660;">(</span><span class="str" style="color:#0880;">"This is pthread_2.\n"</span><span class="pun" style="color:#66660;">);</span><span class="pln">   </span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">}</span><span class="pln">   </span></div><div><span class="pln">  </span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">return</span><span class="pun" style="color:#66660;">;</span><span class="pln">   </span></div><div><span class="pun" style="color:#66660;">}</span><span class="pln">  </span></div><p style="PADDING-BOTTOM: 0px; MARGIN-TOP: 0px; MARGIN-BOTTOM: 10px; PADDING-TOP: 0px"></p>

从上面事例中，可以得到这么一个结果，就是线程一的线程函数一结束就自动释放资源，线程二就得等到pthread_join来释放系统资源。

结束！