Posix多线程编程学习笔记（六）—共享内存（3）

r囧r小猫 2022-06-12 12:28 177阅读 0赞

**五、共享内存区的写入和读出**

上面我们介绍了mmap函数，下面我们就可以通过这些函数，把进程映射到共享内存区。

然后我们就可以通过共享内存区进行进程间通信了。

下面是共享内存区写入的例子：

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 <td> /*shm_write.h写入/读出共享内存区*/ #include &lt;sys/stat.h&gt; #include &lt;fcntl.h&gt; #include &lt;sys/mman.h&gt; #include &lt;unistd.h&gt; &nbsp; int main(int argc,char **argv) { int shm_id; struct stat buf; char *ptr; &nbsp; if(argc!=2) { &nbsp;&nbsp;&nbsp; printf(“usage:shm_open &lt;pathname&gt;/n”); &nbsp;&nbsp;&nbsp; exit(1); } shm_id=shm_open(argv[1],O_RDWR|O_CREAT,0644);/*创建共享内存区*/ ftruncate(shm_id,100);/*修改共享区大小*/ fstat(shm_id,&amp;buf); ptr=mmap(NULL,buf.st_size,PROT_READ|PROT_WRITE,MAP_SHARED,shm_id,0);/*连接共享内存区*/ strcpy(ptr,”hello linux”);/*写入共享内存区*/ printf(“%s/n”,ptr);/*读出共享内存区*/ shm_unlink(argv[1]);/*删除共享内存区*/ } </td> 
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下面是运行结果：

\#cc –lrt –o shm\_write shm\_write.c

\#./shm\_write test

hello linux

**六、程序例子**

下面是利用pisix共享内存区实现进程间通信的例子：服务器进程读出共享内存区内容，然后清空。客户进程向共享内存区写入数据。直到用户输入“q”程序结束。程序用posix信号量实现互斥。

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 <td> /*server.c服务器程序*/ #include &lt;sys/stat.h&gt; #include &lt;fcntl.h&gt; #include &lt;sys/mman.h&gt; #include &lt;unistd.h&gt; #include &lt;semaphore.h&gt; &nbsp; int main(int argc,char **argv) { int shm_id; char *ptr; sem_t *sem; &nbsp; if(argc!=2) { &nbsp;&nbsp;&nbsp; printf(“usage:shm_open &lt;pathname&gt;/n”); &nbsp;&nbsp;&nbsp; exit(1); } shm_id=shm_open(argv[1],O_RDWR|O_CREAT,0644);/*创建共享内存区*/ ftruncate(shm_id,100);/*调整共享内存区大小*/ sem=sem_open(argv[1],O_CREAD,0644,1);/*创建信号量*/ ptr=mmap(NULL,100,PROT_READ|PROT_WRITE,MAP_SHARED,shm_id,0);/*连接共享内存区*/ strcpy(ptr,”/0”); while(1) { &nbsp;&nbsp;&nbsp; if((strcmp(ptr,”/0”))==0)/*如果为空，则等待*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; continue; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; else &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if((strcmp(ptr,”q/n”))==0)/*如果内存为q/n退出循环*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; break; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sem_wait(sem);/*申请信号量*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; printf(“server:%s”,ptr);/*输入共享内存区内容*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; strcpy(ptr,”/0”);/*清空共享内存区*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sem_pose(sem);/*释放信号量*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; } &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sem_unlink(argv[1]);/*删除信号量*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; shm_unlink(argv[1]);/*删除共享内存区*/ &nbsp;&nbsp;&nbsp;&nbsp; } } &nbsp; </td> 
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 <td> /*server.c服务器程序*/ #include &lt;sys/stat.h&gt; #include &lt;fcntl.h&gt; #include &lt;sys/mman.h&gt; #include &lt;unistd.h&gt; #include &lt;semaphore.h&gt; #include &lt;stdio.h&gt; &nbsp; int main(int argc,char **argv) { int shm_id; char *ptr; sem_t *sem; &nbsp; if(argc!=2) { &nbsp;&nbsp;&nbsp; printf(“usage:shm_open &lt;pathname&gt;/n”); &nbsp;&nbsp;&nbsp; exit(1); } shm_id=shm_open(argv[1],0);/*打开共享内存区 sem=sem_open(argv[1],0);/*打开信号量*/ ptr=mmap(NULL,100,PROT_READ|PROT_WRITE,MAP_SHARED,shm_id,0);/*连接共享内存区*/ while(1) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sem_wait(sem);/*申请信号量*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; fgets(ptr,10,stdin);/*从键盘读入数据到共享内存区*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; printf(“user:%s”,ptr); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if((strcmp(ptr,”q/n”))==0) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; exit(0); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sem_pose(sem);/*释放信号量*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sleep(1); &nbsp;&nbsp;&nbsp;&nbsp; } &nbsp;&nbsp;&nbsp;&nbsp; exit(0); } &nbsp; </td> 
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\#cc –lrt –o server server.c

\#cc –lrt –o user user.c

\#./server test&

\#./user test

输入:abc

user:abc

server:abc

输入:123

user:123

server:123

输入:q

user:q