Linux中的sleep、usleep、nanosleep、poll和select

爱被打了一巴掌 2022-03-22 04:12 443阅读 0赞

在进行Linux C/C++编程时，可调用的sleep函数有好多个，那么究竟应当调用哪一个了？下表列出了这几个函数间的异同点，可作为参考：

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 <td style="vertical-align:top;width:54.95pt;"> &nbsp; </td> 
 <td style="vertical-align:top;width:64.2pt;"> 性质 </td> 
 <td style="vertical-align:top;width:39pt;"> 精准度 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 线程安全 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 信号安全 </td> 
 <td style="vertical-align:top;width:169.5pt;"> &nbsp; </td> 
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 <td style="vertical-align:top;width:54.95pt;"> sleep </td> 
 <td style="vertical-align:top;width:64.2pt;"> libc库函数 </td> 
 <td style="vertical-align:top;width:39pt;"> 秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 不能和alarm同时使用 </td> 
 <td style="vertical-align:top;width:169.5pt;"> 有些是基于alarm实现的，所以不能和alarm同时使用 </td> 
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 <td style="vertical-align:top;width:54.95pt;"> usleep </td> 
 <td style="vertical-align:top;width:64.2pt;"> libc库函数 </td> 
 <td style="vertical-align:top;width:39pt;"> 微秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> - </td> 
 <td style="vertical-align:top;width:49.2pt;"> - </td> 
 <td style="vertical-align:top;width:169.5pt;"> POSIX.1-2001已将usleep标注为废弃，POSIX.1-2008已删除usleep，应当使用nanosleep替代usleep </td> 
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 <td style="vertical-align:top;width:54.95pt;"> nanosleep </td> 
 <td style="vertical-align:top;width:64.2pt;"> 系统调用 </td> 
 <td style="vertical-align:top;width:39pt;"> 纳秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 不确定 </td> 
 <td style="vertical-align:top;width:169.5pt;"> 即使被信号中断，也可实现实际睡眠时长不小于参数指定时长 </td> 
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 <td style="vertical-align:top;width:54.95pt;"> clock_nanosleep </td> 
 <td style="vertical-align:top;width:64.2pt;"> 系统调用 </td> 
 <td style="vertical-align:top;width:39pt;"> 纳秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 不确定 </td> 
 <td style="vertical-align:top;width:169.5pt;"> 区别于nanosleep，可选择为相对或绝对时间，其次是可以选择使用哪个时钟 </td> 
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 <td style="vertical-align:top;width:54.95pt;"> poll </td> 
 <td style="vertical-align:top;width:64.2pt;"> 系统调用 </td> 
 <td style="vertical-align:top;width:39pt;"> 毫秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:169.5pt;"> 在协程库libco中可安全使用，如被信号中断，则实际睡眠时长会小于参数指定的时长 </td> 
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 <td style="vertical-align:top;width:54.95pt;"> ppoll </td> 
 <td style="vertical-align:top;width:64.2pt;"> 系统调用 </td> 
 <td style="vertical-align:top;width:39pt;"> 纳秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:169.5pt;"> 如被信号中断，则实际睡眠时长会小于参数指定的时长 </td> 
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 <td style="vertical-align:top;width:54.95pt;"> select </td> 
 <td style="vertical-align:top;width:64.2pt;"> 系统调用 </td> 
 <td style="vertical-align:top;width:39pt;"> 微秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:169.5pt;"> 即使被信号中断，也可实现实际睡眠时长不小于参数指定时长 </td> 
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 <td style="vertical-align:top;width:54.95pt;"> pselect </td> 
 <td style="vertical-align:top;width:64.2pt;"> 系统调用 </td> 
 <td style="vertical-align:top;width:39pt;"> 纳秒 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:49.2pt;"> 是 </td> 
 <td style="vertical-align:top;width:169.5pt;"> 如被信号中断，则实际睡眠时长会小于参数指定的时长 </td> 
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**C/C++常用封装：**

1) 基于nanosleep的毫秒级封装

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 <td style="vertical-align:top;width:426.1pt;"> #include&nbsp;&lt;time.h&gt; void&nbsp;millisleep(uint32_t&nbsp;milliseconds)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;struct&nbsp;timespec&nbsp;ts&nbsp;=&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;milliseconds&nbsp;/&nbsp;1000, &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(milliseconds&nbsp;%&nbsp;1000)&nbsp;*&nbsp;1000000 &nbsp;&nbsp;&nbsp;&nbsp;}; &nbsp;&nbsp;&nbsp;&nbsp;while&nbsp;((-1&nbsp;==&nbsp;nanosleep(&amp;ts,&nbsp;&amp;ts))&nbsp;&amp;&amp;&nbsp;(EINTR&nbsp;==&nbsp;errno)); } </td> 
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2) 基于nanosleep的微秒级封装

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 <td style="vertical-align:top;width:426.1pt;"> #include&nbsp;&lt;time.h&gt; void&nbsp;microsleep(uint32_t&nbsp;microseconds)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;struct&nbsp;timespec&nbsp;ts&nbsp;=&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;microseconds&nbsp;/&nbsp;1000000, &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(microseconds&nbsp;%&nbsp;1000000)&nbsp;*&nbsp;1000 &nbsp;&nbsp;&nbsp;&nbsp;}; &nbsp;&nbsp;&nbsp;&nbsp;while&nbsp;((-1&nbsp;==&nbsp;nanosleep(&amp;ts,&nbsp;&amp;ts))&nbsp;&amp;&amp;&nbsp;(EINTR&nbsp;==&nbsp;errno)); } </td> 
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3) 基于poll的秒级封装

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 <td style="vertical-align:top;width:426.1pt;"> //&nbsp;可libco协程库中安全使用 void&nbsp;pollsleep(int&nbsp;milliseconds)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;(void)poll(NULL,&nbsp;0,&nbsp;milliseconds); } </td> 
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4) 基于select的毫秒级封装

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 <td style="vertical-align:top;width:426.1pt;"> void&nbsp;selectsleep(int&nbsp;milliseconds)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;struct&nbsp;timeval&nbsp;timeout&nbsp;=&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;milliseconds&nbsp;/&nbsp;1000, &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(milliseconds&nbsp;%&nbsp;1000) &nbsp;&nbsp;&nbsp;&nbsp;}; &nbsp;&nbsp;&nbsp;&nbsp;struct&nbsp;timeval&nbsp;old_timeout&nbsp;=&nbsp;{&nbsp;timeout.tv_sec,&nbsp;timeout.tv_usec&nbsp;}; &nbsp;&nbsp;&nbsp;&nbsp;while&nbsp;(true)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(void)select(0,&nbsp;NULL,&nbsp;NULL,&nbsp;NULL,&nbsp;&amp;timeout); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(timeout.tv_sec&lt;=0&nbsp;&amp;&amp;&nbsp;timeout.tv_usec&lt;=0) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;break; &nbsp;&nbsp;&nbsp;&nbsp;} } </td> 
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如果开发环境是C++11或更高版本，则可直接使用C++标准库提供的：

5) 毫秒睡眠

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 <td style="vertical-align:top;width:426.1pt;"> #if&nbsp;__cplusplus&nbsp;&gt;=&nbsp;201103L #include&nbsp;&lt;chrono&gt; #include&nbsp;&lt;system_error&gt; #include&nbsp;&lt;thread&gt; &nbsp; std::this_thread::sleep_for(std::chrono::milliseconds(1000)); #endif&nbsp;//&nbsp;__cplusplus&nbsp;&gt;=&nbsp;201103L </td> 
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6) 微秒睡眠

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 <td style="vertical-align:top;width:426.1pt;"> #if&nbsp;__cplusplus&nbsp;&gt;=&nbsp;201103L #include&nbsp;&lt;chrono&gt; #include&nbsp;&lt;system_error&gt; #include&nbsp;&lt;thread&gt; &nbsp; std::this_thread::sleep_for(std::chrono::microseconds(1000)); #endif&nbsp;//&nbsp;__cplusplus&nbsp;&gt;=&nbsp;201103L </td> 
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上述介绍的sleep函数均不方便控制它们提前结束，如果需要这种sleep，可基于**pthread\_cond\_timedwait**实现，实现可参考CEvent源码：

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 <td style="vertical-align:top;width:426.1pt;"> <a href="https://github.com/eyjian/libmooon/blob/master/src/sys/event.cpp" rel="nofollow">https://github.com/eyjian/libmooon/blob/master/src/sys/event.cpp</a> </td> 
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