Linux进程通信：命名管道FIFO小结.doc

Linux下进程之间通信可以用命名管道FIFO完成。命名管道是一种特殊类型的文件，因为Linux中所有事物都是文件，它在文件系统中以文件名的形式存在。在程序中，我们可以使用两个不同的函数调用来建立管道：#include #include int mkfifo(const char *filename, mode_t mode);int mknode(const char *filename, mode_t mode | S_IFIFO, (dev_t) 0 ); 下面先来创建一个管道：view plaincopy to clipboardprint?#include #include #include #include int main() int res = mkfifo(/tmp/my_fifo, 0777); if (res = 0) printf(FIFO createdn); exit(EXIT_SUCCESS); #include #include #include #include int main() int res = mkfifo(/tmp/my_fifo, 0777); if (res = 0) printf(FIFO createdn); exit(EXIT_SUCCESS); 编译这个程序：gcc o fifo1.c fifo 运行这个程序：$ ./fifo1 用ls命令查看所创建的管道$ ls -lF /tmp/my_fifo prwxr-xr-x 1 root root 0 05-08 20:10 /tmp/my_fifo|注意：ls命令的输出结果中的第一个字符为p，表示这是一个管道。最后的|符号是由ls命令的-F选项添加的，它也表示是这是一个管道。虽然，我们所设置的文件创建模式为“0777”，但它被用户掩码（umask）设置（022）给改变了，这与普通文件创建是一样的，所以文件的最终模式为755。打开FIFO一个主要的限制是，程序不能是O_RDWR模式打开FIFO文件进行读写操作，这样做的后果未明确定义。这个限制是有道理的，因为我们使用FIFO只是为了单身传递数据，所以没有必要使用O_RDWR模式。如果一个管道以读/写方式打开FIFO，进程就会从这个管道读回它自己的输出。如果确实需要在程序之间双向传递数据，最好使用一对FIFO，一个方向使用一个。当一个Linux进程被阻塞时，它并不消耗CPU资源，这种进程的同步方式对CPU而言是非常有效率的。有关Linux下命名管道FIFO的读写规则可以参见之前所写的一篇文章：Linux命名管道FIFO的读写规则。 一、实验：使用FIFO实现进程间通信两个独立的程序：1. 生产者程序，它在需要时创建管道，然后尽可能快地向管道中写入数据。2. 消费者程序，它从FIFO中读取数据并丢弃它们。 生产者程序fifo2.c：view plaincopy to clipboardprint?#include #include #include #include #include #include #include #define FIFO_NAME /tmp/Linux/my_fifo #define BUFFER_SIZE PIPE_BUF #define TEN_MEG (1024 * 1024 * 10) int main() int pipe_fd; int res; int open_mode = O_WRONLY; int bytes = 0; char bufferBUFFER_SIZE + 1; if (access(FIFO_NAME, F_OK) = -1) res = mkfifo(FIFO_NAME, 0777); if (res != 0) fprintf(stderr, Could not create fifo %sn, FIFO_NAME); exit(EXIT_FAILURE); printf(Process %d opening FIFO O_WRONLYn, getpid(); pipe_fd = open(FIFO_NAME, open_mode); printf(Process %d result %dn, getpid(), pipe_fd); if (pipe_fd != -1) while (bytes TEN_MEG) res = write(pipe_fd, buffer, BUFFER_SIZE); if (res = -1) fprintf(stderr, Write error on pipen); exit(EXIT_FAILURE); bytes += res; close(pipe_fd); else exit(EXIT_FAILURE); printf(Process %d finishn, getpid(); exit(EXIT_SUCCESS); #include #include #include #include #include #include #include #define FIFO_NAME /tmp/Linux/my_fifo#define BUFFER_SIZE PIPE_BUF#define TEN_MEG (1024 * 1024 * 10)int main() int pipe_fd; int res; int open_mode = O_WRONLY; int bytes = 0; char bufferBUFFER_SIZE + 1; if (access(FIFO_NAME, F_OK) = -1) res = mkfifo(FIFO_NAME, 0777); if (res != 0) fprintf(stderr, Could not create fifo %sn, FIFO_NAME); exit(EXIT_FAILURE); printf(Process %d opening FIFO O_WRONLYn, getpid(); pipe_fd = open(FIFO_NAME, open_mode); printf(Process %d result %dn, getpid(), pipe_fd); if (pipe_fd != -1) while (bytes TEN_MEG) res = write(pipe_fd, buffer, BUFFER_SIZE); if (res = -1) fprintf(stderr, Write error on pipen); exit(EXIT_FAILURE); bytes += res; close(pipe_fd); else exit(EXIT_FAILURE); printf(Process %d finishn, getpid(); exit(EXIT_SUCCESS); 消费者程序fifo3.c：view plaincopy to clipboardprint?#include #include #include #include #include #include #include #define FIFO_NAME /tmp/Linux/my_fifo #define BUFFER_SIZE PIPE_BUF int main() int pipe_fd; int res; int open_mode = O_RDONLY; char bufferBUFFER_SIZE + 1; int bytes = 0; memset(buffer, 0, sizeof(buffer); printf(Process %d opeining FIFO O_RDONLYn, getpid(); pipe_fd = open(FIFO_NAME, open_mode); printf(Process %d result %dn, getpid(), pipe_fd); if (pipe_fd != -1) do res = read(pipe_fd, buffer, BUFFER_SIZE); bytes += res; while(res 0); close(pipe_fd); else exit(EXIT_FAILURE); printf(Process %d finished, %d bytes readn, getpid(), bytes); exit(EXIT_SUCCESS); #include #include #include #include #include #include #include #define FIFO_NAME /tmp/Linux/my_fifo#define BUFFER_SIZE PIPE_BUFint main() int pipe_fd; int res; int open_mode = O_RDONLY; char bufferBUFFER_SIZE + 1; int bytes = 0; memset(buffer, 0, sizeof(buffer); printf(Process %d opeining FIFO O_RDONLYn, getpid(); pipe_fd = open(FIFO_NAME, open_mode); printf(Process %d result %dn, getpid(), pipe_fd); if (pipe_fd != -1) do res = read(pipe_fd, buffer, BUFFER_SIZE); bytes += res; while(res 0); close(pipe_fd); else exit(EXIT_FAILURE); printf(Process %d finished, %d bytes readn, getpid(), bytes); exit(EXIT_SUCCESS); 编译这两个程序：gcc o fifo2 fifo2.cgcc o fifo3 fifo3.c 运行这两个程序：rootlocalhost chaper12# ./fifo2 & 后台执行，写数据2 23121Process 23121 opening FIFO O_WRONLYrootlocalhost chaper12# time ./fifo3读数据Process 24155 opeining FIFO O_RDONLYProcess 23121 result 3Process 24155 result 3Process 23121 finishProcess 24155 finished, 10485760 bytes read2- Done ./fifo2 real 0m0.214suser 0m0.000ssys 0m0.179s 以上两个程序均是使用阻塞模式FIFO。Linux会安排好这两个进程之间的调试，使它们在可以运行的时候运行，在不能运行的时候阻塞。因此，写进程将在管道满时阻塞，读进程将在管道空时阻塞。虚拟机上，time命令显示，读进程只运行了0.2秒的时间，却读取了10M字节的数据。这说明管道在程序之间传递数据是非常有效的。 二、实验：使用FIFO的客户/服务器应用程序 利用FIFO实现一个客户/服务器的应用程序，服务器进程接受请求，对它们进程处理，最后把结果数据返回给发送请求的客户方。 首先建立一个头文件client.h，它定义了客户和服务器程序都要用到的数据结构，并包含了必要的头文件。view plaincopy to clipboardprint?#include #include #include #include #include #include #include #define SERVER_FIFO_NAME /tmp/Linux/chaper12/server_fifo #define CLIENT_FIFO_NAME /tmp/Linux/chaper12/client_%d_fifo #define BUFFER_SIZE PIPE_BUF #define MESSAGE_SIZE 20 #define NAME_SIZE 256 typedef struct message pid_t client_pid; char dataMESSAGE_SIZE + 1; message; #include #include #include #include #include #include #include #define SERVER_FIFO_NAME /tmp/Linux/chaper12/server_fifo#define CLIENT_FIFO_NAME /tmp/Linux/chaper12/client_%d_fifo#define BUFFER_SIZE PIPE_BUF#define MESSAGE_SIZE 20#define NAME_SIZE 256typedef struct message pid_t client_pid; char dataMESSAGE_SIZE + 1;message; 接下来是服务器程序server.c，在这一部分，是以只读阻塞模式打开服务器管道，用于接收客户发送过来的数据，这些数据采用message结构体封装。view plaincopy to clipboardprint?#include client.h int main() int server_fifo_fd; int client_fifo_fd; int res; char client_fifo_nameNAME_SIZE; message msg; char *p; if (mkfifo(SERVER_FIFO_NAME, 0777) = -1) fprintf(stderr, Sorry, create server fifo failure!n); exit(EXIT_FAILURE); server_fifo_fd = open(SERVER_FIFO_NAME, O_RDONLY); if (server_fifo_fd = -1) fprintf(stderr, Sorry, server fifo open failure!n); exit(EXIT_FAILURE); sleep(5); while (res = read(server_fifo_fd, &msg, sizeof(msg) 0) p = msg.data; while (*p) *p = toupper(*p); +p; sprintf(client_fifo_name, CLIENT_FIFO_NAME, msg.client_pid); client_fifo_fd = open(client_fifo_name, O_WRONLY); if (client_fifo_fd = -1) fprintf(stderr, Sorry, client fifo open failure!n); exit(EXIT_FAILURE); write(client_fifo_fd, &msg, sizeof(msg); close(client_fifo_fd); close(server_fifo_fd); unlink(SERVER_FIFO_NAME); exit(EXIT_SUCCESS); #include client.hint main() int server_fifo_fd; int client_fifo_fd; int res; char client_fifo_nameNAME_SIZE; message msg; char *p; if (mkfifo(SERVER_FIFO_NAME, 0777) = -1) fprintf(stderr, Sorry, create server fifo failure!n); exit(EXIT_FAILURE); server_fifo_fd = open(SERVER_FIFO_NAME, O_RDONLY); if (server_fifo_fd = -1) fprintf(stderr, Sorry, server fifo open failure!n); exit(EXIT_FAILURE); sleep(5); while (res = read(server_fifo_fd, &msg, sizeof(msg) 0) p = msg.data; while (*p) *p = toupper(*p); +p; sprintf(client_fifo_name, CLIENT_FIFO_NAME, msg.client_pid); client_fifo_fd = open(client_fifo_name, O_WRONLY); if (client_fifo_fd = -1) fprintf(stderr, Sorry, client fifo open failure!n); exit(EXIT_FAILURE); write(client_fifo_fd, &msg, sizeof(msg); close(client_fifo_fd); close(server_fifo_fd); unlink(SERVER_FIFO_NAME); exit(EXIT_SUCCESS); 客户端程序client.c，这个程序用于向服务器发送消息，并接收来自服务器的回复。view plaincopy to clipboardprint?#include client.h int main() int server_fifo_fd; int client_fifo_fd; int res; char client_fifo_nameNAME_SIZE; message msg; msg.client_pid = getpid(); sprintf(client_fifo_name, CLIENT_FIFO_NAME, msg.client_pid); if (mkfifo(client_fifo_name, 0777) = -1) fprintf(stderr, Sorry, create client fifo failure!n); exit(EXIT_FAILURE); server_fifo_fd = open(SERVER_FIFO_NAME, O_WRONLY); if (server_fifo_fd = -1) fprintf(stderr, Sorry, open server fifo failure!n); exit(EXIT_FAILURE); sprintf(msg.data, Hello from %d, msg.client_pid); printf(%d sent %s , msg.client_pid, msg.data); write(server_fifo_fd, &msg, sizeof(msg); client_fifo_fd = open(client_fifo_name, O_RDONLY); if (client_fifo_fd = -1) fprintf(stderr, Sorry, client fifo open failure!n); exit(EXIT_FAILURE); res = read(client_fifo_fd, &msg, sizeof(msg); if (res 0) printf(received:%sn, msg.data); close(client_fifo_fd); close(server_fifo_fd); unlink(client_fifo_name); exit(EXIT_SUCCESS); #include client.hint main() int server_fifo_fd; int client_fifo_fd; int res; char client_fifo_nameNAME_SIZE; message msg; msg.client_pid = getpid(); sprintf(client_fifo_name, CLIENT_FIFO_NAME, msg.client_pid); if (mkfifo(client_fifo_name, 0777) = -1) fprintf(stderr, Sorry, create client fifo failure!n); exit(EXIT_FAILURE); server_fifo_fd = open(SERVER_FIFO_NAME, O_WRONLY); if (server_fifo_fd = -1) fprintf(stderr, Sorry, open server fifo failure!n); exit(EXIT_FAILURE); sprintf(msg.data, Hello from %d, msg.client_pid); printf(%d sent %s , msg.client_pid, msg.data); write(server_fifo_fd, &msg, sizeof(msg); client_fifo_fd = open(client_fifo_name, O_RDONLY); if (client_fifo_fd = -1) fprintf(stderr, Sorry, client fifo open failure!n); exit(EXIT_FAILURE); res = read(client_fifo_fd, &msg, sizeof(msg); if (res 0) printf(received:%sn, msg.data); close(client_fifo_fd); close(server_fifo_fd); unlink(client_fifo_name); exit(EXIT_SUCCESS); 编译程序：gcc o server server.cgcc o client client.c 测试这个程序，我们需要一个服务器进程和多个客户进程。为了让多个客户进程在同一时间启动，我们使用了shell命令：rootlocalhost chaper12# ./