linux 进程间通信--systemV 信号量 实例

#include <stdio.h>
#include <sys/types.h>
#include <sys/sem.h>
#include <errno.h>
#include <stdlib.h>
#include <signal.h>
#define MAX_SEMAPHORES  3
union semun
{int val;                   			/* value for SETVAL */struct semid_ds *buf;       		/* buffer for IPC_STAT, IPC_SET */unsigned short int *array;  		/* array for GETALL, SETALL */struct seminfo *__buf;      		/* buffer for IPC_INFO */
};
static int set_semvalue(int sem_id,int semIndex,int semValue)
{union semun sem_union;int value;sem_union.val = semValue;if (semctl(sem_id, semIndex, SETVAL, sem_union) == -1){return(0);}printf("set value success,");printf("init value is %d\n",get_semvalue(sem_id,semIndex));return(1);
}int get_semvalue(int sem_id,int semIndex)
{int res;if((res=semctl(sem_id, semIndex, GETVAL)) == -1){perror("semctl");exit(EXIT_FAILURE);}return res;
}static int semaphore_v(int sem_id,int semIndex)
{struct sembuf sem_b;sem_b.sem_num = semIndex;sem_b.sem_op = 1; /* V() *///sem_b.sem_flg = SEM_UNDO;sem_b.sem_flg=IPC_NOWAIT; //0if (semop(sem_id, &sem_b, 1) == -1){perror("semop");return(0);}return(1);
}static int semaphore_p(int sem_id,int semIndex)
{struct sembuf sem_b;sem_b.sem_num = semIndex;sem_b.sem_op = -1; /* V() *///sem_b.sem_flg = SEM_UNDO;sem_b.sem_flg=IPC_NOWAIT;//0if (semop(sem_id, &sem_b, 1) == -1){perror("semop");return(0);}return(1);
}
void signalHandler(int sig)
{printf("child process exit\n");exit(EXIT_SUCCESS);
}
void semphorePV()
{pid_t childPid;int i;int value;key_t key;int status;int chlid_sem_id,parent_sem_id,semIndex=0,semValue=MAX_SEMAPHORES;if((childPid=fork())==-1){perror("fork");exit(EXIT_FAILURE);}else if(childPid==0){
#if 1struct sigaction sa;sa.sa_handler = signalHandler;sa.sa_flags = 0;	/* Interrupt system calls */sigemptyset(&sa.sa_mask);sigaction(SIGINT, &sa, NULL);sigaction(SIGQUIT, &sa, NULL);
#endifif((chlid_sem_id=semget((key_t)123456,1,IPC_CREAT|0770))==-1){perror("semget");exit(EXIT_FAILURE);}if (!set_semvalue(chlid_sem_id,semIndex,semValue)){fprintf(stderr, "Failed to initialize semaphore\n");exit(EXIT_FAILURE);}value=get_semvalue(chlid_sem_id,semIndex);printf("this is child,the current value is %d\n",value);if(!semaphore_v(chlid_sem_id,semIndex)){fprintf(stderr, "Failed to v operator\n");exit(EXIT_FAILURE);}value=get_semvalue(chlid_sem_id,semIndex);printf("child V operator,the current value is %d\n",value);printf("--------------------------------------------------\n");while(1){if(!semaphore_v(chlid_sem_id,semIndex)){fprintf(stderr, "Failed to v operator\n");exit(EXIT_FAILURE);}value=get_semvalue(chlid_sem_id,semIndex);printf("child V operator,the current value is %d\n",value);sleep(2);}printf("child exit success\n");exit(EXIT_SUCCESS);}else	//parent{sleep(1);if((parent_sem_id=semget((key_t)123456,1,IPC_CREAT|0770))==-1){perror("semget");exit(EXIT_FAILURE);}value=get_semvalue(parent_sem_id,semIndex);printf("this is parent ,the current value is %d\n",value);sleep(1);if(!semaphore_p(parent_sem_id,semIndex)){fprintf(stderr, "Failed to v operator\n");exit(EXIT_FAILURE);}printf("parent P operator,the current value is %d\n",value);printf("################################################################\n");while(1){if(!semaphore_p(parent_sem_id,semIndex)){fprintf(stderr, "Failed to v operator\n");break;}else{value=get_semvalue(parent_sem_id,semIndex);printf("parent P operator,the current value is %d\n",value);}sleep(1);}kill(childPid,SIGINT);sleep(2);if(semctl(parent_sem_id,0, IPC_RMID,(struct msquid_ds*)0)==-1){perror("semctl");exit(EXIT_FAILURE);}else{printf("the parent remove the sem\n");}return 0;}
}
int main(int argc,char *argv)
{semFunTest(argc,argv);semphorePV();
}int semFunTest(int argc,char *argv[]){int i, ret, semid;unsigned short sem_write_array[MAX_SEMAPHORES];unsigned short sem_read_array[MAX_SEMAPHORES];union semun arg;if((semid = semget( IPC_PRIVATE, MAX_SEMAPHORES,IPC_CREAT | 0666 )) == -1){perror("semget");exit(EXIT_FAILURE);}/* Initialize the sem_array */for (i = 0 ; i < MAX_SEMAPHORES ; i++ ){sem_write_array[i] = (unsigned short)(i+1);}/* Update the arg union with the sem_array address */arg.array = sem_write_array;/* Set the values of the semaphore-array */if((ret = semctl( semid, 0, SETALL, arg)) == -1){perror("SETALL failed\n");}/* Update the arg union with another array for read */arg.array = sem_read_array;/* Read the values of the semaphore array */if((ret = semctl( semid, 0, GETALL, arg)) == -1){printf("GETALL failed (%d)\n", errno);}/* print the sem_read_array */for ( i = 0 ; i < MAX_SEMAPHORES ; i++ ){printf("Semaphore %d, value %d\n", i, sem_read_array[i] );}printf("************************************************\n");/* Use GETVAL in a similar manner */for ( i = 0 ; i < MAX_SEMAPHORES ; i++ ){ret = semctl( semid, i, GETVAL );printf("Semaphore %d, value %d\n", i, ret );}/* Delete the semaphore */if(semctl(semid,0, IPC_RMID,(struct msquid_ds*)0)==-1){perror("semctl");exit(EXIT_FAILURE);}else{printf("remove the sem\n");}return 0;
}

2：执行结果