对信号集与信号量的理解
参考如下链接：http://www.c-lang.net/semctl/index.html 不过是日语的。
把他的程序重新改动一下，改为一次性为信号集合申请两个信号量：
代码变成：
#include <stdio.h> #include <unistd.h> #include <sys/wait.h> #include <stdlib.h> #include <sys/sem.h> #define LOCK -1 #define UNLOCK 1 /* semophore operation (lock/unlock) */ void Semop01(int SemId,int Op); /* semophore operation (lock/unlock) */ void Semop02(int SemId,int Op); int main() { FILE *fp01 , *fp02; int semid; union semun { int val; /* value for SETVAL*/ struct semid_ds *buf; /* buffer for IPC_STAT,IPC_SET using */ unsigned short *array; /* array for GETALL,SETALL */ } ctl_arg; char *file01 = "./sem01.txt"; int child_cnt01; int line_cnt01; if ((fp01 = fopen(file01,"w")) == NULL) { perror("main : fopen "); exit(EXIT_FAILURE); } setvbuf(fp01,NULL,_IONBF,0); char *file02 = "./sem02.txt"; int child_cnt02; int line_cnt02; if ((fp02 = fopen(file02,"w")) == NULL) { perror("main : fopen "); exit(EXIT_FAILURE); } setvbuf(fp02,NULL,_IONBF,0); /* to create one semophore array which hold two semophore */ if ((semid = semget(IPC_PRIVATE,2,0600)) == -1){ perror("main : semget "); exit(EXIT_FAILURE); } /* initialize the first semophore with value 1*/ ctl_arg.val = 1; if (semctl(semid,0,SETVAL,ctl_arg) == -1){ perror("main : semctl "); exit(EXIT_FAILURE); } /* initialize the second semophore with value 1*/ ctl_arg.val = 1; if (semctl(semid,1,SETVAL,ctl_arg) == -1){ perror("main : semctl "); exit(EXIT_FAILURE); } /* fork three child process*/ for (child_cnt01 = 0; child_cnt01 < 3; ++child_cnt01) { if (fork() == 0) { /* child process */ printf("child process %d begin\n",child_cnt01 + 1); Semop01(semid,LOCK); /*lock*/ for (line_cnt01 = 1; line_cnt01 <= 5; ++line_cnt01) { fprintf(fp01,"child process %d msg : %d\n", child_cnt01 + 1,line_cnt01); sleep(1); } Semop01(semid,UNLOCK); /* unlock*/ printf("child process %d ends\n",child_cnt01 + 1); exit(EXIT_SUCCESS); } } /* fork another two child process*/ for (child_cnt02 = 0; child_cnt02< 2; ++child_cnt02) { if (fork() == 0) { /* child process */ printf("another child process %d begin\n", child_cnt02 + 1); Semop02(semid,LOCK); /*lock*/ for (line_cnt02 = 1; line_cnt02 <= 5; ++line_cnt02) { fprintf(fp02,"another child process %d msg : %d\n", child_cnt02 + 1,line_cnt02); sleep(1); } Semop02(semid,UNLOCK); /* unlock*/ printf("another child process %d ends\n",child_cnt02 + 1); exit(EXIT_SUCCESS); } } /* parent process, waitint for child process ending */ for (child_cnt01 = 0; child_cnt01 < 5; ++child_cnt01) { wait(NULL); } /* delete semophore array*/ if (semctl(semid,0,IPC_RMID,ctl_arg) == -1){ perror("main : semctl "); exit(EXIT_FAILURE); } fclose(fp01); fclose(fp02); printf("parenet process ends\n"); return EXIT_SUCCESS; } /* semophore operation (lock/unlock) */ void Semop01(int p_semid,int p_op) { struct sembuf sops[1]; sops[0].sem_num = 0; /* semophore number*/ sops[0].sem_op = p_op; /* semophore operation*/ sops[0].sem_flg = 0; /* operation flag*/ if (semop(p_semid,sops,1) == -1) { perror("Semop01 "); exit(EXIT_FAILURE); } return; } /* semophore operation (lock/unlock) */ void Semop02(int p_semid,int p_op) { struct sembuf sops[2]; sops[0].sem_num=0; sops[0].sem_op=0; sops[0].sem_flg=0; sops[1].sem_num = 1; /* semophore number*/ sops[1].sem_op = p_op; /* semophore operation*/ sops[1].sem_flg = 0; /* operation flag*/ if (semop(p_semid,sops,2) == -1) { perror("Semop02 "); exit(EXIT_FAILURE); } return; }
其中，三个子进程用第一个信号量，另外两个子进程用第二个信号量。互不干扰。
运行结果：
child process 1 begin
child process 2 begin
child process 3 begin
another child process 1 begin
another child process 2 begin
child process 1 ends
another child process 1 ends
child process 2 ends
another child process 2 ends
child process 3 ends
parenet process ends
文件内容：
[root@gaorhel01 gao]# cat sem01.txt
child process 1 msg : 1
child process 1 msg : 2
child process 1 msg : 3
child process 1 msg : 4
child process 1 msg : 5
child process 2 msg : 1
child process 2 msg : 2
child process 2 msg : 3
child process 2 msg : 4
child process 2 msg : 5
child process 3 msg : 1
child process 3 msg : 2
child process 3 msg : 3
child process 3 msg : 4
child process 3 msg : 5
[root@gaorhel01 gao]# cat sem02.txxt
cat: sem02.txxt: No such file or directory
[root@gaorhel01 gao]# cat sem02.txt
another child process 1 msg : 1
another child process 1 msg : 2
another child process 1 msg : 3
another child process 1 msg : 4
another child process 1 msg : 5
another child process 2 msg : 1
another child process 2 msg : 2
another child process 2 msg : 3
another child process 2 msg : 4
another child process 2 msg : 5