?? p11.8.c
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#include <stdio.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/sem.h>union semun{ int val; struct semid_ds * buf; unsigned short int * array; struct seminfo * __buf;};int main(int argc,char* argv[]){ int semid; pid_t pid; int proj_id; key_t key; int num; int i,j; union semun arg; static struct sembuf acquire={0,-1,SEM_UNDO}; static struct sembuf release={0,1,SEM_UNDO}; if(argc!=2){ printf("Usage : %s num\n",argv[0]); return -1; } num=atoi(argv[1]); proj_id=2; key=ftok("/home/program",proj_id); if(key==-1){ perror("cannot generate the IPC key"); return -1; } semid=semget(key,1,IPC_CREAT | IPC_EXCL | 0666); if(semid==-1){ perror("cannot create semaphore set"); return -1; } static unsigned short start_var=1; arg.array=1; if(semctl(semid,0,SETVAL,arg)==-1){ perror("cannot set semaphore set"); return -1; } for(i=0;i<num;i++){ pid=fork(); if(pid<0){ perror("cannot create new process"); return -1; }else if(pid==0){ semid=semget(key,1,0); if(semid==-1){ perror("cannot let the process get the access right"); _exit(-1); } for(j=0;j<2;j++){ sleep(i); if(semop(semid,&acquire,1)==-1){ perror("cannot acquire the resource"); _exit(-1); } printf("====enter the critical section=====\n"); printf("---pid : % ld ---\n",(long)getpid()); sleep(1); printf("====leave the critical section=====\n"); if(semop(semid,&release,1)==-1){ perror("cannot release the resource"); _exit(-1); } } _exit(0); } } for(i=0;i<num;i++) wait(NULL); if(semctl(semid,0,IPC_RMID,0)==-1){ perror("cannot remove the semaphore set"); return -1; } return 0;}?? 快捷鍵說明
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