#include<unistd.h>
#include<signal.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/wait.h>
#include<semaphore.h>
#include<sys/sem.h>
#include <sys/stat.h>

#include<fcntl.h>

int main(){
	int pid1,pid2;
	sem_t *resource1;
	sem_t *resource2;
	char inpipe[200],outpipe1[100],outpipe2[100];
	int fd[2];				//0为读出段,1为写入端
	pipe(fd);				//建立一个无名管道

	pid1 = fork();
	if(pid1<0){
		printf("error in the first fork!");
	}
	else if(pid1==0){	//子进程1
		printf("[%s|%u]Current: %u\n", __FUNCTION__, __LINE__, getpid());
		printf("Pid of PID[1]: %u\n", getpid());

		resource1=sem_open("name_sem1",O_CREAT,0666,0);		// 有名信号量打开，name_sem1
		close(fd[0]);		//关掉读出端
		lockf(fd[1],1,0);	// 管道持锁, 锁定从当前偏移量到文件结尾的区域
		sprintf(outpipe1,"Child process 1 is sending a message!\n");
		write(fd[1],outpipe1, strlen(outpipe1));
		lockf(fd[1],0,0);	// 管道解锁
		sem_post(resource1);		// 信号量开锁，name_sem1
		sem_close(resource1);					// 有名信号量关闭，name_sem1

		exit(0);		// 线程退出
	}

	pid2 = fork();
	if(pid2<0){
		printf("error in the second fork!\n");
	}else if(pid2==0){	// 子进程2
		printf("[%s|%u]Current: %u\n", __FUNCTION__, __LINE__, getpid());
		resource1=sem_open("name_sem1",O_CREAT,0666,0);
		resource2=sem_open("name_sem2",O_CREAT,0666,0);

		sem_wait(resource1);
		printf("Pid of PID[2]: %u\n", getpid());
		close(fd[0]);
		lockf(fd[1],1,0);
		sprintf(outpipe2,"Child process 2 is sending a message!\n");
		write(fd[1],outpipe2, strlen(outpipe2));
		lockf(fd[1],0,0);
		sem_post(resource2);

		sem_close(resource1);
		sem_close(resource2);

		exit(0);
	}

	if(pid1 > 0 && pid2 >0){
		printf("[%s|%u]Current: %u\n", __FUNCTION__, __LINE__, getpid());
		resource2=sem_open("name_sem2",O_CREAT,0666,0);

		sem_wait(resource2);	// 信号量持锁，source2
		printf("Current: %u\n", getpid());

		waitpid(pid1,NULL,0);	// 等待子线程1状态变化(退出)；
		waitpid(pid2,NULL,0);	// 等待子线程2状态变化(退出)；

		close(fd[1]);		//关掉写端
		read(fd[0],inpipe,200);
		printf("%s\n",inpipe);

		sem_close(resource2);

		exit(0);		// 进程退出，正常
	}

	sem_unlink("name_sem1");	// 信号量销毁，
	sem_unlink("name_sem2");

	return 0;
}