一 进程之间为什么要进行通信？
1. 数据传输 一个进程需要将数据发送到另外一个进程；
2. 资源共享 多个进程之间需要贡献资源；
3. 通知事件 一个进程需要向另外一个线程或一组线程发送消息，通知他们发送了某种事件；
4. 进程控制 有些进程希望完全控制另外一个线程的执行，此时控制进程希望能获取被控制线程的所有操作和运行状态。
二 进程间常用的通信方式
1. 无名管道和有名管道；
2. 信号；
3. 消息队列；
4. 共享内存；
5. 信号量；
6. 套接字。
三 进程间使用无名管道和有名管道进行通信
无名管道（pipe）：只能适用于父进程和子进程之间进行通信；
有名管道（fifo）: 适用于所有进程之间进行通信。
四 pipe通信方式例子
#include <stdlib.h>#include <stdio.h>#include <unistd.h>#include <string.h>#include <sys/wait.h>int main(int args, char *argv[]){ int pipe_fd[2]; pid_t pid; char buf[100]; int r_num; int w_num; memset(buf,0,sizeof(buf)); if(pipe(pipe_fd)<0) { printf("Pipe creat error!\n"); return 0; } if((pid=fork())==0) { close(pipe_fd[1]); printf("I am the child!\n"); sleep(2); if((r_num=read(pipe_fd[0],buf,100))>0) { printf("%d bytes read from the pipe is %s\n", r_num, buf); close(pipe_fd[0]); exit(0); } } else if(pid>0){ printf("I am the paraent!\n"); close(pipe_fd[0]); if(write(pipe_fd[1],"Hello",5)!=-1) printf("paraent writes hello\n"); if(write(pipe_fd[1]," pipe!",7)!=-1) printf("paraent writes pipe\n"); close(pipe_fd[1]); sleep(3); waitpid(-1,NULL,0); exit(0); }}
输出结果：
I am the paraent!paraent writes helloparaent writes pipeI am the child!12 bytes read from the pipe is Hello pipe!
五 有名管道通信例子（FIFO）
fifo_read.cpp
#include <stdlib.h>#include <stdio.h>#include <unistd.h>#include <string.h>#include <sys/wait.h>#include <errno.h>#include <sys/types.h>#include <fcntl.h>#include <sys/stat.h>#define FIFO "/home/dxx/myfifo"int main(int args, char* argv[]){char buf_r[100];int fd = 0;int num_read = 0;if(mkfifo(FIFO,O_CREAT|O_EXCL)<0 && (errno != EEXIST))printf("Can not creat fifoserver!\n");printf("Preparing for reading bytes...\n");memset(buf_r,0,sizeof(buf_r));fd = open(FIFO,O_RDONLY|O_NONBLOCK,0);if(fd == -1){perror("open error!");}while(1){memset(buf_r,0,sizeof(buf_r));if((num_read = read(fd, buf_r, 100)) == -1){if(errno == EAGAIN)printf("No data yet!\n");}printf("Read %d bytes data is %s\n", num_read,buf_r);sleep(1);}}
fifo_write.cpp
#include <stdlib.h>#include <stdio.h>#include <unistd.h>#include <string.h>#include <sys/wait.h>#include <errno.h>#include <sys/types.h>#include <fcntl.h>#include <sys/stat.h>#define FIFO_SERVE "/home/dxx/myfifo"int main(int args, char* argv[]){int fd = 0;int num_write = 0;char buf_w[100];if(args == 1)printf("Please enter data you want to write!\n");fd = open(FIFO_SERVE,O_WRONLY|O_NONBLOCK,0);if(fd == -1){perror("Open Error!");}printf("Preparing to write bytes\n");strcpy(buf_w,argv[1]);num_write = write(fd, buf_w, 3);if(num_write == -1){printf("errno is %d\n",errno);if(errno == EAGAIN)perror("No data to read");}printf("%d bytes data has been written, data is %s\n", num_write, buf_w);}
输出结果：
Read 0 bytes data is Read 0 bytes data is Read 0 bytes data is Read 0 bytes data is Read 0 bytes data is Read 3 bytes data is 123Read 0 bytes data is Read 0 bytes data is Read 0 bytes data is Read 0 bytes data is Read 0 bytes data is Read 0 bytes data is
怠惰是贫穷的制造厂。
