IPC之FIFO
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简介
FIFO又被称为命名管道，它是一种特殊类型的文件，它在文件系统中以文件名的形式存在，一般的文件I/O函数都可以用于FIFO。
打开一个FIFO时，非阻塞标志(O_NONBLOCK)产生下列影响：
- 未指定O_NONBLOCK
只读open()要阻塞到某个其他进程为写而打开此FIFO。类似的，只写open()要阻塞到某个其他进程为读而打开它。
- 指定O_NONBLOCK
只读open()立即返回。但是，如果没有进程已经为读而打开一个FIFO，那么只写open()将出错返回-1，其errno是ENXIO。
基于O_NONBLOCK对FIFO操作的影响，一种比较好的操作FIFO的方式是以非阻塞的方式打开文件，然后以阻塞的方式读写文件或使用select。
一个给定的FIFO有多个写进程是很常见的。这意味着如果不希望多个进程写的数据互相穿插，则需考虑原子操作，常量PIPE_BUF说明了可被原子地写到FIFO的最大数据量。
FIFO有以下两种用途：
- FIFO由shell命令使用以便将数据从一条管道线传送到另一条，为此不需要创建中间临时文件。
- FIFO用于客户进程-服务器进程的应用程序中，以在客户进程和服务器进程中传递数据。
示例程序
阻塞版本
服务端
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <sys/stat.h>#define RECV_BUF_SIZE 1024#define SEND_BUF_SIZE 1024#define CONTENT_LEN 128#define ARGUMENT_LEN 128#define DATA_SEPARATOR ':'#define SERVER_FIFO_PATH "/tmp/fifo_server"int server_write_fd, server_read_fd, client_write_fd;char send_buf[SEND_BUF_SIZE];charcontent[CONTENT_LEN];charclient_fifo_path[ARGUMENT_LEN];char recv_buf[RECV_BUF_SIZE];char send_buf[SEND_BUF_SIZE];static int fifo_mode = S_IRUSR| S_IWUSR| S_IRGRP| S_IWGRP;/* * create server fifo * success : 0 failed : -1 */int fifo_init(void){int ret;struct stat filestat;ret = stat(SERVER_FIFO_PATH, &filestat);if(ret == 0){if (unlink(SERVER_FIFO_PATH) < 0){perror("Cannot delete old MI fifo");return -1;}}else if(ret < 0 && errno != ENOENT){perror("MI FIFO stat failed");return -1;} if((mkfifo(SERVER_FIFO_PATH, fifo_mode) < 0)){ perror("Create client fifo error"); return -1; } if((chmod(SERVER_FIFO_PATH, fifo_mode) < 0)){ perror("Chmod client fifo error");goto error; }return 0;error: remove(SERVER_FIFO_PATH);return -1;}/* * open server fifo * success : fd failed : -1 */int open_client_fifo(char *pipe_name){ int flags; if(!pipe_name || *pipe_name == 0){ printf("No server fifo to open\n"); return -1; } client_write_fd = open(pipe_name, O_WRONLY|O_NONBLOCK); if(client_write_fd < 0){ perror("Can't open server fifo error"); return -1; } if((flags = fcntl(client_write_fd, F_GETFL, 0)) < 0){ perror("Server fifo F_GETFL error"); goto error; } flags&=~O_NONBLOCK; if(fcntl(client_write_fd, F_SETFL, flags) < 0){ perror("Server fifo F_GETFL error"); goto error; } return 0;error: close(client_write_fd); return -1;}/* * open server fifo for reading * success : fd failed : -1 */int open_server_fifo(char * pipe_name){ int flags; if(!pipe_name || *pipe_name == 0){ printf("No client fifo to open"); return -1; } server_read_fd = open(pipe_name, O_RDONLY|O_NONBLOCK); if(server_read_fd < 0){ printf("Can't open client fifo for reading"); return -1; } server_write_fd = open(pipe_name, O_WRONLY|O_NONBLOCK); if(server_write_fd < 0){ printf("Can't open client fifo for writing"); return -1; } if((flags = fcntl(server_read_fd, F_GETFL, 0)) < 0){ printf("Client fifo F_GETFL error"); goto error; } flags&=~O_NONBLOCK; if(fcntl(server_read_fd, F_SETFL, flags) < 0){ printf("Client fifo F_SETFL error"); goto error; } return 0;error: close(server_read_fd); close(server_write_fd); return -1;}int data_parse(void){char*p, *postion;p = recv_buf;if(*p != DATA_SEPARATOR){printf("command must begin with %c\n", DATA_SEPARATOR);return -1;}p++;postion = strchr(p, DATA_SEPARATOR);if(postion == NULL){printf("file separator missing in fifo command\n");return -1;}strncpy(client_fifo_path, p, postion - p);p = ++postion;strncpy(content, p, strlen(p));return 0;}int main(int argc, char *argv[]){ int ret; if(fifo_init()){return -1; } if(open_server_fifo(SERVER_FIFO_PATH)){goto error; } while(1){memset(recv_buf, 0, RECV_BUF_SIZE);if((ret = read(server_read_fd, recv_buf, RECV_BUF_SIZE)) > 0){if(data_parse()){continue;}printf("Receive data from <%s> : %s\n",client_fifo_path, content); if(open_client_fifo(client_fifo_path)){continue; }sprintf(send_buf, "hello, %s\n", client_fifo_path);ret = write(client_write_fd, send_buf, strlen(send_buf));if(ret < 0){perror("Write data to client fifo error");continue;}}}exit(EXIT_SUCCESS);error:remove(SERVER_FIFO_PATH);exit(EXIT_FAILURE);}客户端
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <sys/stat.h>#define SERVER_FIFO_PATH "/tmp/fifo_server"#define CLIENT_FIFO_PATH "/tmp/fifo_client_%d"#define SEND_BUF_SIZE 1024#define RECV_BUF_SIZE 1024#define CLIENT_FIFO_SIZE 128int server_write_fd, client_read_fd, client_write_fd;charclient_fifo[CLIENT_FIFO_SIZE];char send_buf[SEND_BUF_SIZE];static int fifo_mode = S_IRUSR| S_IWUSR| S_IRGRP| S_IWGRP;/* * create client fifo * success : 0 failed : -1 */int fifo_init(void){int ret;struct stat filestat;memset(client_fifo, 0, CLIENT_FIFO_SIZE);sprintf(client_fifo, CLIENT_FIFO_PATH, getpid());ret = stat(client_fifo, &filestat);if(ret == 0){if (unlink(client_fifo) < 0){perror("Cannot delete old MI fifo");return -1;}}else if(ret < 0 && errno != ENOENT){perror("MI FIFO stat failed");return -1;} if((mkfifo(client_fifo, fifo_mode) < 0)){ perror("Create client fifo error"); return -1; } if((chmod(client_fifo, fifo_mode) < 0)){ perror("Chmod client fifo error");goto error; }return 0;error: remove(client_fifo);return -1;}/* * open server fifo for writing * success : fd failed : -1 */int open_server_fifo(char *pipe_name){ int flags; if(!pipe_name || *pipe_name == 0){ printf("No server fifo to open\n"); return -1; } server_write_fd = open(pipe_name, O_WRONLY|O_NONBLOCK); if(server_write_fd < 0){ perror("Can't open server fifo error"); return -1; } if((flags = fcntl(server_write_fd, F_GETFL, 0)) < 0){ perror("Server fifo F_GETFL error"); goto error; } flags&=~O_NONBLOCK; if(fcntl(server_write_fd, F_SETFL, flags) < 0){ perror("Server fifo F_GETFL error"); goto error; } return 0;error: close(server_write_fd); return -1;}/* * open client fifo * success : fd failed : -1 */int open_client_fifo(char * pipe_name){ int flags; if(!pipe_name || *pipe_name == 0){ printf("No client fifo to open.\n"); return -1; } client_read_fd = open(pipe_name, O_RDONLY|O_NONBLOCK); if(client_read_fd < 0){ printf("Can't open client fifo for reading"); return -1; } client_write_fd = open(pipe_name, O_WRONLY|O_NONBLOCK); if(client_write_fd < 0){ printf("Can't open client fifo for writing\n"); return -1; } if((flags = fcntl(client_read_fd, F_GETFL, 0)) < 0){ printf("Client fifo F_GETFL error.\n"); goto error; } flags&=~O_NONBLOCK; if(fcntl(client_read_fd, F_SETFL, flags) < 0){ printf("Client fifo F_SETFL error.\n"); goto error; } return 0;error: close(client_read_fd); close(client_write_fd); return -1;}int main(int argc, char *argv[]){ int ret; char recv_buf[RECV_BUF_SIZE]; if(fifo_init()){return -1; } if(open_client_fifo(client_fifo)){goto error1; } if(open_server_fifo(SERVER_FIFO_PATH)){goto error2; }sprintf(send_buf, ":%s:hello, server.", client_fifo); ret = write(server_write_fd, send_buf, strlen(send_buf)); if(ret < 0){ perror("Write data to server fifo error");goto error3; }memset(recv_buf, 0, RECV_BUF_SIZE); if((ret = read(client_read_fd, recv_buf, RECV_BUF_SIZE)) > 0){printf("Receive data form server : %s", recv_buf);} close(client_read_fd); close(server_write_fd); remove(client_fifo);exit(EXIT_SUCCESS);error3:close(server_write_fd);error2:close(client_read_fd);close(client_write_fd);error1: remove(client_fifo);exit(EXIT_FAILURE);}select版本
服务端
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <sys/stat.h>#define RECV_BUF_SIZE 1024#define SEND_BUF_SIZE 1024#define CONTENT_LEN 128#define ARGUMENT_LEN 128#define DATA_SEPARATOR ':'#define SERVER_FIFO_PATH "/tmp/fifo_server"int server_write_fd, server_read_fd, client_write_fd;char send_buf[SEND_BUF_SIZE];charcontent[CONTENT_LEN];charclient_fifo_path[ARGUMENT_LEN];char recv_buf[RECV_BUF_SIZE];char send_buf[SEND_BUF_SIZE];static int fifo_mode = S_IRUSR| S_IWUSR| S_IRGRP| S_IWGRP;/* * create server fifo * success : 0 failed : -1 */int fifo_init(void){int ret;struct stat filestat;ret = stat(SERVER_FIFO_PATH, &filestat);if(ret == 0){if (unlink(SERVER_FIFO_PATH) < 0){perror("Cannot delete old MI fifo");return -1;}}else if(ret < 0 && errno != ENOENT){perror("MI FIFO stat failed");return -1;} if((mkfifo(SERVER_FIFO_PATH, fifo_mode) < 0)){ perror("Create client fifo error"); return -1; } if((chmod(SERVER_FIFO_PATH, fifo_mode) < 0)){ perror("Chmod client fifo error");goto error; }return 0;error: remove(SERVER_FIFO_PATH);return -1;}/* * open server fifo * success : fd failed : -1 */int open_client_fifo(char *pipe_name){ int flags; if(!pipe_name || *pipe_name == 0){ printf("No server fifo to open\n"); return -1; } client_write_fd = open(pipe_name, O_WRONLY|O_NONBLOCK); if(client_write_fd < 0){ perror("Can't open server fifo error"); return -1; } if((flags = fcntl(client_write_fd, F_GETFL, 0)) < 0){ perror("Server fifo F_GETFL error"); goto error; } flags&=~O_NONBLOCK; if(fcntl(client_write_fd, F_SETFL, flags) < 0){ perror("Server fifo F_GETFL error"); goto error; } return 0;error: close(client_write_fd); return -1;}/* * open server fifo for reading * success : fd failed : -1 */int open_server_fifo(char * pipe_name){ //int flags; if(!pipe_name || *pipe_name == 0){ printf("No client fifo to open"); return -1; } server_read_fd = open(pipe_name, O_RDONLY|O_NONBLOCK); if(server_read_fd < 0){ printf("Can't open client fifo for reading"); return -1; } return 0;}int data_parse(void){char*p, *postion;p = recv_buf;if(*p != DATA_SEPARATOR){printf("command must begin with %c\n", DATA_SEPARATOR);return -1;}p++;postion = strchr(p, DATA_SEPARATOR);if(postion == NULL){printf("file separator missing in fifo command\n");return -1;}strncpy(client_fifo_path, p, postion - p);p = ++postion;strncpy(content, p, strlen(p));return 0;}int main(int argc, char *argv[]){ int ret, maxfd;fd_setset, read_set;structtimeval timeout; if(fifo_init()){return -1; } if(open_server_fifo(SERVER_FIFO_PATH)){goto error; }FD_ZERO(&set);FD_SET(server_read_fd, &set); maxfd = server_read_fd + 1; while(1){read_set = set;timeout.tv_sec = 2;timeout.tv_usec = 0;memset(recv_buf, 0, RECV_BUF_SIZE);ret = select(maxfd, &read_set, NULL, NULL, &timeout);switch(ret){case 0:continue;case -1:perror("select");continue;default:if(FD_ISSET(server_read_fd, &read_set)){if((ret = read(server_read_fd,recv_buf, RECV_BUF_SIZE)) > 0){if(data_parse()){continue;}printf("Receive data from <%s> : %s\n",client_fifo_path, content); if(open_client_fifo(client_fifo_path)){continue; }sprintf(send_buf, "hello, %s\n", client_fifo_path);ret = write(client_write_fd, send_buf, strlen(send_buf));if(ret < 0){perror("Write data to client fifo error");continue;}}}}}remove(SERVER_FIFO_PATH);exit(EXIT_SUCCESS);error:remove(SERVER_FIFO_PATH);exit(EXIT_FAILURE);}客户端
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <sys/stat.h>#define RECV_BUF_SIZE 1024#define SEND_BUF_SIZE 1024#define CONTENT_LEN 128#define ARGUMENT_LEN 128#define DATA_SEPARATOR ':'#define SERVER_FIFO_PATH "/tmp/fifo_server"int server_write_fd, server_read_fd, client_write_fd;char send_buf[SEND_BUF_SIZE];charcontent[CONTENT_LEN];charclient_fifo_path[ARGUMENT_LEN];char recv_buf[RECV_BUF_SIZE];char send_buf[SEND_BUF_SIZE];static int fifo_mode = S_IRUSR| S_IWUSR| S_IRGRP| S_IWGRP;/* * create server fifo * success : 0 failed : -1 */int fifo_init(void){int ret;struct stat filestat;ret = stat(SERVER_FIFO_PATH, &filestat);if(ret == 0){if (unlink(SERVER_FIFO_PATH) < 0){perror("Cannot delete old MI fifo");return -1;}}else if(ret < 0 && errno != ENOENT){perror("MI FIFO stat failed");return -1;} if((mkfifo(SERVER_FIFO_PATH, fifo_mode) < 0)){ perror("Create client fifo error"); return -1; } if((chmod(SERVER_FIFO_PATH, fifo_mode) < 0)){ perror("Chmod client fifo error");goto error; }return 0;error: remove(SERVER_FIFO_PATH);return -1;}/* * open server fifo * success : fd failed : -1 */int open_client_fifo(char *pipe_name){ int flags; if(!pipe_name || *pipe_name == 0){ printf("No server fifo to open\n"); return -1; } client_write_fd = open(pipe_name, O_WRONLY|O_NONBLOCK); if(client_write_fd < 0){ perror("Can't open server fifo error"); return -1; } if((flags = fcntl(client_write_fd, F_GETFL, 0)) < 0){ perror("Server fifo F_GETFL error"); goto error; } flags&=~O_NONBLOCK; if(fcntl(client_write_fd, F_SETFL, flags) < 0){ perror("Server fifo F_GETFL error"); goto error; } return 0;error: close(client_write_fd); return -1;}/* * open server fifo for reading * success : fd failed : -1 */int open_server_fifo(char * pipe_name){ //int flags; if(!pipe_name || *pipe_name == 0){ printf("No client fifo to open"); return -1; } server_read_fd = open(pipe_name, O_RDONLY|O_NONBLOCK); if(server_read_fd < 0){ printf("Can't open client fifo for reading"); return -1; } return 0;}int data_parse(void){char*p, *postion;p = recv_buf;if(*p != DATA_SEPARATOR){printf("command must begin with %c\n", DATA_SEPARATOR);return -1;}p++;postion = strchr(p, DATA_SEPARATOR);if(postion == NULL){printf("file separator missing in fifo command\n");return -1;}strncpy(client_fifo_path, p, postion - p);p = ++postion;strncpy(content, p, strlen(p));return 0;}int main(int argc, char *argv[]){ int ret, maxfd;fd_setset, read_set;structtimeval timeout; if(fifo_init()){return -1; } if(open_server_fifo(SERVER_FIFO_PATH)){goto error; }FD_ZERO(&set);FD_SET(server_read_fd, &set); maxfd = server_read_fd + 1; while(1){read_set = set;timeout.tv_sec = 2;timeout.tv_usec = 0;memset(recv_buf, 0, RECV_BUF_SIZE);ret = select(maxfd, &read_set, NULL, NULL, &timeout);switch(ret){case 0:continue;case -1:perror("select");continue;default:if(FD_ISSET(server_read_fd, &read_set)){if((ret = read(server_read_fd,recv_buf, RECV_BUF_SIZE)) > 0){if(data_parse()){continue;}printf("Receive data from <%s> : %s\n",client_fifo_path, content); if(open_client_fifo(client_fifo_path)){continue; }sprintf(send_buf, "hello, %s\n", client_fifo_path);ret = write(client_write_fd, send_buf, strlen(send_buf));if(ret < 0){perror("Write data to client fifo error");continue;}}}}}remove(SERVER_FIFO_PATH);exit(EXIT_SUCCESS);error:remove(SERVER_FIFO_PATH);exit(EXIT_FAILURE);} 0 0
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