管道的相关知识

1.信号类型 
信号事件的发生有两个来源：硬件来源和软件来源。

下面是几种常见的信号： 
§ SIGHUP： 从终端上发出的结束信号 
§ SIGINT： 来自键盘的中断信号（Ctrl-C） 
§ SIGSTOP：来自键盘（Ctrl-Z）或调试程序的停止执行信号，暂停进程 
§ SIGKILL：该信号结束接收信号的进程，杀死进程 
§ SIGTERM：kill 命令发出的信号 
§ SIGCHLD：子进程停止或结束时通知父进程

2.信号处理方式

当某信号出现时，将按照下列三种方式中 
的一种进行处理： 
1）、忽略此信号 
大多数信号都按照这种方式进行处理，但有两种信号决不能被忽略,它们是： 
SIGKILL\SIGSTOP。 
这两种信号不能被忽略的原因是：它们向超级用户提供了一种终止或停止进程的方法 
2）、执行用户希望的动作 
通知内核在某种信号发生时，调用一个用户函数。在用户函数中，执行用户希望的处理 
3）、执行系统默认动作 
对大多数信号的系统默认动作是终止该进程

3.信号函数 
1）kill 
函数作用：传送信号给指定的进程 
函数原型：int kill(pid_t pid, int signo） 
参数：

pid参数有四种不同的情况： 
1、pid>0 
将信号发送给进程ID为pid的进程。 
2、pid == 0 
将信号发送给同组的进程。 
3、pid < 0 
将信号发送给其进程组ID等于pid绝对值的进程。 
4、pid ==－1 
将信号发送给所有进程

返回值：成功为0，失败为-1； 
头文件： 
#include <sys/types.h> 
#include <signal.h>

函数例子：

<code class="hljs perl has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#include <stdio.h></span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#include <stdlib.h></span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#include <signal.h></span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#include <sys/types.h></span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#include <sys/wait.h></span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> main() { pid_t pid; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ret; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>((pid=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">fork</span>()) < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { perror(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fork"</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">exit</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(pid == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { raise(SIGSTOP); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">exit</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"pid=<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%d</span>\n"</span>, pid); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>((<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">waitpid</span>(pid, NULL, WNOHANG)) == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">kill</span>(pid,SIGKILL); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kill <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%d</span>\n"</span>, pid); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> { perror(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kill"</span>); } } }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0553388; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li></ul>

执行结果： 
pid=25831 
kill 25831 

找到进程号，并且杀死该进程。

2.raise 
函数作用：发送信号给自身 
函数原型：int raise(int signo) 
返回值：成功为0，失败为-1； 
头文件： 
#include <sys/types.h> 
#include <signal.h>

程序例子

<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/types.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/stat.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <errno.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <fcntl.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <stdio.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <stdlib.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <string.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <signal.h></span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/wait.h></span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> main() { pid_t pid; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ret; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>((pid= fork()) < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Fork error.\n"</span>); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">exit</span>(-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(pid == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"child (pid:%d) is waiting for any signal\n."</span>, getpid()); raise(SIGSTOP); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">exit</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>((waitpid(pid, NULL, WNOHANG)) == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { kill(pid, SIGKILL); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"parent kill child process %d\n"</span>, pid); } waitpid(pid, NULL, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">exit</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); } }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0553388; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li></ul>

执行结果 
child (pid:25923) is waiting for any signal 
parent kill child process 25923 

子进程等待该进程的信号，父进程杀死子进程。

3.alarm 
函数作用：设置信号传送时钟 
函数原型：unsigned int alarm(unsigned int seconds) 
参数：seconds： 经过了指定的seconds秒后会产生信号SIGALRM。 
返回值：成功为0，失败为-1； 
头文件： 
#include <sys/types.h> 
#include <signal.h>

4.pause 
函数作用：让进程暂停直到信号出现 
函数原型：int pause(void) 
说明：令目前进程暂停进入睡眠状态，直到被信号中断 
头文件： 
#include <unistd.h>

5.signal 
函数作用：设置信号处理方式 
函数原型：void (*signal (int signo, void (* sighandler_t)(int)))(int) 
说明：如何理解？

<code class="hljs vala has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">typedef <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (*sighandler_t)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>)  sighandler_t ; sighandler_t <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">signal</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> signum, sighandler_t handler))</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0553388; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

func可能的值是： 
1、SIG_IGN：忽略此信号 
2、SIG_DFL: 按系统默认方式处理 
3、信号处理函数名：使用该函数处理

头文件： 
#include <sinal.h>