If two processes not only need to be synchronized, but also to ensure the order of execution, it is necessary to use two semaphores (mutual exclusion locks) to solve the problem.
//Fence model: Implement the four subprocesses in the following framework. After all processes complete their tasks, execute the next time together
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include < sys/wait.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdlib.h>
#include <signal.h>
#define PROCESS_NR 4
void sigFunc(int signo)
{
int semId;
semId=semget(0x555,PROCESS_NR+1,IPC_CREAT|0600);
if(semId>0){
semctl(semId,0,IPC_RMID);
}
exit(1);
}
void p_lock(int idx,int semId);
void waitZero(int semId);
void doWork(int idx,int semId);
int main(void)
{
int semId,i;
pid_t pid;
//////////////////////////////
//The corresponding subscript semaphore controls the last one of the corresponding child process Semaphore control parent process
semId=semget(0x555,PROCESS_NR+1,IPC_CREAT|0600);
if(semId==-1)
{
perror("create sem");
return 11;
}
//init sem value
unsigned short vals[ PROCESS_NR+1]={0}; //Initialize multiple semaphore values
if(semctl(semId,0,SETALL,vals)==-1)
{
perror("init sem val");
semctl(semId, 0,IPC_RMID);
return 12;
}
/////////////////////////////
for(i=0;i<PROCESS_NR ;i++)
{
pid=fork();
if(pid==-1) return 1;
else if(pid==0)//child process
{
doWork(i,semId);//i identifies the number of the process
exit(0);
}
}
//
signal(SIGINT ,sigFunc);
//parent
struct sembuf bufs[PROCESS_NR+1]={0};
for(i=0;i<PROCESS_NR;i++)// Subprocess
{
bufs[i].sem_num=i;
bufs[i] .sem_op =1;
}
bufs[PROCESS_NR].sem_num=PROCESS_NR;//Father's resource
bufs[PROCESS_NR].sem_op =PROCESS_NR;
//////////////////// //////////////////
while(1)
{
waitZero(semId);
printf("========Raise the fence========\n");
semop(semId,bufs,PROCESS_NR+1);
}
while(wait(NULL)!=-1)
; //empty
return 0;
}
void doWork(int idx,int semId)
{
pid_t pid=getpid();
int sec;
srand(pid);
while(1)
{
p_lock(idx,semId);
sec=rand()% 10+1;
printf("%dth Do [%d] sec:%d\n",idx,pid,sec);
//Sleep randomly for 1-10s, simulating different processes and doing things at different times may require different
sleep durations (sec);
//Notify the parent process that the child process has finished
executing p_lock(PROCESS_NR,semId);
}
}
////////////////////////// /////////////
void p_lock(int idx,int semId)
{
struct sembuf buf={.sem_num=idx,.sem_op=-1};
semop(semId,&buf,1);
}
void waitZero(int semId)
{
struct sembuf buf={.sem_num=PROCESS_NR,.sem_op=0};
semop(semId,&buf,1);
}