使用信号量实现父子进程间同步：
#include <sys/sem.h>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <sys/wait.h>union semun { int val; /* Value for SETVAL */ struct semid_ds *buf; /* Buffer for ipC_STAT, IPC_SET */ unsigned short *array; /* Array for GETALL, SETALL */ struct seminfo *__buf; /* Buffer for IPC_INFO (linux-specific) */};void pv(int sem_id, int op) { struct sembuf sem_b; sem_b.sem_num = 0; sem_b.sem_op = op; sem_b.sem_flg = SEM_UNDO; semop(sem_id, &sem_b, 1); }int main(int argc, char** argv){ int sem_id = semget(IPC_PRIVATE, 1, 0666); union semun sem_un; sem_un.val = 1; semctl(sem_id, 0, SETVAL, sem_un); pid_t pid = fork(); if(pid < 0) return -1; else if(pid == 0){ printf("child try to get binary sem/n"); pv(sem_id, -1); printf("child get the sem and would release it after 5 seconds/n"); sleep(5); pv(sem_id, 1); exit(0); } else{ printf("parent try to get binary sem/n"); pv(sem_id, -1); printf("parent get the sem and would release it agter 5 SEOcnds/n"); sleep(5); pv(sem_id, 1); } waitpid(pid, NULL, 0); semctl(sem_id, 0, IPC_RMID, sem_un); return 0;}使用消息队列实现简单的进程间交谈。
utili.h头文件：
#pragma once#include <stdio.h>#include <sys/ipc.h>#include <sys/msg.h>#include <stdlib.h>#include <string.h>const char* const PATH_NAME = "pathname";const int PRO_ID = 0xff;const int BUFFER_SIZE = 256;struct message { long msg_type; char msg_text[BUFFER_SIZE];};server.cpp：
#include "utili.h"const int SERVER_MSG_SND_TYPE = 10000;const int SERVER_MSG_RCV_TYPE = 2;int main(){ int msg_id; if(msg_id = msgget(ftok(PATH_NAME, PRO_ID), IPC_CREAT | IPC_EXCL | 0755) < 0){ perror("what"); exit(-1); } printf("msg_id = %d/n", msg_id); message msg; for(; ;){ printf("server:>"); scanf("%s", msg.msg_text); if(strncasecmp(msg.msg_text, "quit", 4) == 0) break; msg.msg_type = SERVER_MSG_SND_TYPE; msgsnd(msg_id, &msg, strlen(msg.msg_text)+1, 0); msgrcv(msg_id, &msg, BUFFER_SIZE, SERVER_MSG_RCV_TYPE, 0); printf("client:>%s/n", msg.msg_text); } msgctl(msg_id, IPC_RMID, 0); while(1); exit(0);客户端：
#include "utili.h"const int CLIENT_MSG_SND_TYPE = 2;const int CLIENT_MSG_RCV_TYPE = 10000;int main(){ int msg_id; key_t msg_key = ftok(PATH_NAME, PRO_ID); if(msg_key < 0){ perror("what1"); exit(-1); } printf("msg_key = %d/n", msg_key); if((msg_id = msgget(msg_key, 0)) < 0){ perror("what2"); exit(-1); } printf("mid_id = %d/n", msg_id); message msg; for(; ;){ msgrcv(msg_id, &msg, BUFFER_SIZE, CLIENT_MSG_RCV_TYPE, 0); printf("serverhehf:>%s/n", msg.msg_text); printf("clientwowo:>"); scanf("%s", msg.msg_text); if(strncasecmp(msg.msg_text, "quit", 4) == 0) break; msg.msg_type = CLIENT_MSG_SND_TYPE; msgsnd(msg_id, &msg, strlen(msg.msg_text)+1, 0); } msgctl(msg_id, IPC_RMID, 0); exit(0);}双反接收和发送的消息类型不同，可以利用这点从消息队列中取自己的消息。
昨天晚上写消息队列这个程序坑了我好长时间，没有使用perror判断错误外加没有注意到ftok函数针对的path必须是真实存在的文件或目录，然后找BUG找了一个半多小时。
这里使用共享内存来实现服务器和客户端通信，并且由于共享了读写，使用信号量来同步。
utili.h：
#include <stdio.h>#include <sys/shm.h>#include <sys/sem.h>#include <sys/ipc.h>#include <stdlib.h>#include <string.h>#define PATHNAME "newfile"#define PRO_ID 0xff#define err_exit(m) / do{ / perror(m); / exit(1); / }while(0)#define USE_SEMunion semun { int val; /* Value for SETVAL */ struct semid_ds *buf; /* Buffer for IPC_STAT, IPC_SET */ unsigned short *array; /* Array for GETALL, SETALL */ struct seminfo *__buf; /* Buffer for IPC_INFO*/ };server.cpp：
#include "utili.h"int main(int argc, char** argv){ int shm_id; if( (shm_id = shmget(ftok(PATHNAME, PRO_ID), 1024, IPC_CREAT|IPC_EXCL|0755)) < 0) err_exit("shmget err."); char *ch; if( (ch = (char *)shmat(shm_id, NULL, 0)) == (void *)-1) err_exit("shmat err");#ifdef USE_SEM int sem_id; if( (sem_id = semget(ftok(PATHNAME, PRO_ID), 2, IPC_CREAT|IPC_EXCL|0755)) < 0){ shmdt(ch); shmctl(shm_id, IPC_RMID, 0); err_exit("semget err."); } union semun init; init.val = 0; semctl(sem_id, 0, SETVAL, init); //0 semctl(sem_id, 1, SETVAL, init); //1 struct sembuf p = {0, -1, 0}, v = {1, 1, 0};#endif for(; ;){ printf("server:>"); scanf("%s", ch); if(strncasecmp(ch, "quit", 4) == 0){ shmdt(ch); break; } semop(sem_id, &v, 1); semop(sem_id, &p, 1); printf("client:>%s/n", ch); } int res; if( (res = shmctl(shm_id, IPC_RMID, 0)) < 0) err_exit("remove err."); return 0;}client.cpp：
#include "utili.h"int main(int argc, char** argv){ int shm_id; if( (shm_id = shmget(ftok(PATHNAME, PRO_ID), 0, 0)) < 0) err_exit("shmget err."); char *ch; if( (ch = (char *)shmat(shm_id, NULL, 0)) == (void *)-1) err_exit("shmat err");#ifdef USE_SEM int sem_id; if( (sem_id = semget(ftok(PATHNAME, PRO_ID), 0, 0)) < 0){ shmdt(ch); shmctl(shm_id, IPC_RMID, 0); err_exit("semget err."); } union semun init; init.val = 0; semctl(sem_id, 0, SETVAL, init); //0 semctl(sem_id, 1, SETVAL, init); //1 struct sembuf p = {1, -1, 0}, v = {0, 1, 0};#endif for(; ;){ semop(sem_id, &p, 1); printf("server:>%s/n", ch); printf("cli:>"); scanf("%s", ch); if(strncasecmp(ch, "quit", 4) == 0){ shmdt(ch); break; } semop(sem_id, &v, 1); } int res; if( (res = shmctl(shm_id, IPC_RMID, 0)) < 0) err_exit("remove err."); return 0;}新闻热点
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