对信号集与信号量的理解

#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;    
}