这里的信号量主要是在不同的进程之间使用。需要四个操作
- P操作V操作以及通过semctl调用command参数设置SETVAL来初始化信号量,在使用信号量之前必须要这么做.并且可以通过semctl调用command设置为IPC_RMID来删除信号量ID:
因为库里没有定义union semun,因此需要自己定义.
用到信号量的三个函数
- semget 用来创建一个新信号量或者取得一个已有信号量的键semop 用来改变信号量的值semctl 用来直接控制信号量信息，比如semop之前必须先用semctl给个初值
<code class=" hljs cpp" style="box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; padding: 0.5em; color: rgb(0, 0, 0); border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; display: block; background-color: transparent !important;"><span class="hljs-preprocessor" style="box-sizing: border-box; color: rgb(136, 0, 0);">#include<unistd.h></span><span class="hljs-preprocessor" style="box-sizing: border-box; color: rgb(136, 0, 0);">#include<stdlib.h></span><span class="hljs-preprocessor" style="box-sizing: border-box; color: rgb(136, 0, 0);">#include<stdio.h></span><span class="hljs-preprocessor" style="box-sizing: border-box; color: rgb(136, 0, 0);">#include<sys/sem.h></span><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">union</span> semun{ <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> val; <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">struct</span> semid_ds *buf; <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">unsigned</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">short</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> *<span class="hljs-built_in" style="box-sizing: border-box; font-weight: bold;">array</span>; <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">struct</span> seminfo *__buf;};<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> set_semvalue(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>);<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span> del_semvalue(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>);<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> semaphore_p(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>);<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> semaphore_v(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>);<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> sem_id;<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> set_semvalue(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>){ <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">union</span> semun sem_union; sem_union.val=<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>; semctl(sem_id,<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">0</span>,SETVAL,sem_union);}<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span> del_semvalue(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>){ <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">union</span> semun sem_union; semctl(sem_id,<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">0</span>,IPC_RMID,sem_union);}<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> semaphore_p(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>){ <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">struct</span> sembuf sem_b; sem_b.sem_num=<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">0</span>; sem_b.sem_op=-<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>; sem_b.sem_flg=SEM_UNDO;<span class="hljs-comment" style="box-sizing: border-box; color: rgb(136, 136, 136);">//auto release</span> semop(sem_id,&sem_b,<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>);}<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> semaphore_v(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">void</span>){ <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">struct</span> sembuf sem_b; sem_b.sem_num=<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">0</span>; sem_b.sem_op=<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>; sem_b.sem_flg=SEM_UNDO;<span class="hljs-comment" style="box-sizing: border-box; color: rgb(136, 136, 136);">//auto release</span> semop(sem_id,&sem_b,<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>);}<span class="hljs-comment" style="box-sizing: border-box; color: rgb(136, 136, 136);">//main function</span><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> main(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> argc,<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">char</span> *agrv[]){ <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> i; <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span> pause_time; <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">char</span> op_char=<span class="hljs-string" style="box-sizing: border-box; color: rgb(136, 0, 0);">'O'</span>; srand((<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">unsigned</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">int</span>)getpid()); sem_id=semget((key_t)<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1234</span>,<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>,<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">0666</span>|IPC_CREAT); <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">if</span>(argc><span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>) { set_semvalue(); op_char=<span class="hljs-string" style="box-sizing: border-box; color: rgb(136, 0, 0);">'X'</span>; sleep(<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">2</span>); } <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">for</span>(i=<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">0</span>;i<<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">10</span>;i++) { semaphore_p(); <span class="hljs-built_in" style="box-sizing: border-box; font-weight: bold;">printf</span>(<span class="hljs-string" style="box-sizing: border-box; color: rgb(136, 0, 0);">"%c"</span>,op_char); fflush(stdout); pause_time=rand()%<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">3</span>; sleep(pause_time); <span class="hljs-built_in" style="box-sizing: border-box; font-weight: bold;">printf</span>(<span class="hljs-string" style="box-sizing: border-box; color: rgb(136, 0, 0);">"%c"</span>,op_char); fflush(stdout); semaphore_v(); pause_time=rand()%<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">2</span>; sleep(pause_time); } <span class="hljs-built_in" style="box-sizing: border-box; font-weight: bold;">printf</span>(<span class="hljs-string" style="box-sizing: border-box; color: rgb(136, 0, 0);">"\n%d - finished\n"</span>,getpid()); <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">if</span>(argc><span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">1</span>) { sleep(<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">10</span>); del_semvalue(); } <span class="hljs-built_in" style="box-sizing: border-box; font-weight: bold;">exit</span>(<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 136, 0);">0</span>);}</code>
jiang@ubuntu:~/myTest./sem11&[1]12839jiang@ubuntu:~/myTest./sem1OOXXOOXXOOXXOOXXOOXXXXOOXXOOXXOOXXOOXXOO
12839 – finished12840 – finishedjiang@ubuntu:~/myTest$
原来和文字沾上边的孩子从来都是不快乐的，
