【Linux】 多线程编程(信号量实现同步)

该问题如下：

有一个有限缓冲区（在这里使用命名管道实现FIFO式缓冲区）和两个线程：生产者和消费者

一个生产者在缓冲区满的时候必须等待，消费者在缓冲区为空的时候也必须等待

在该程序中定义3个信号量：

avail：表示有界缓冲区中的空单元数，初始值为N

full：表示有界缓冲区中非空单元数，初始值为0

mutex：互斥信号量，初始值为1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ipc.h>
#include <semaphore.h>
#include <errno.h>
#include <pthread.h>

#define MYFIFO "myfifo"

#define BUFFER_SIZE 3		/*缓冲区的个数*/
#define UNIT_SIZE 5		/*每个缓冲区大小*/
#define RUN_TIME 30		/*线程运行时间*/
#define DELAY_TIME_LEVELS 5.0	

int fd;
time_t end_time;
sem_t mutex,avail,full;

const char *content = "hello";

void *producer(void *arg)
{
	int len;
	int delay;

	while(time(NULL)<end_time)
	{
		delay = (int)(rand()*DELAY_TIME_LEVELS/(RAND_MAX)/2.0)+1;
		sleep(delay);
		//sem_wait()和sem_trywait()都相当于P操作,二者的区别在于
		//sem_wait()会阻塞进程,而sem_trywait()会立即返回
		sem_wait(&avail);
		sem_wait(&mutex);

		printf("Producer: delay = %d\n",delay);
		if((len = write(fd,content,strlen(content)))==-1)
		{
			if(errno = EAGAIN)
			{
				printf("The FIFO has not been read yet!\n");
			}
		}
		else
		{
			printf("write %d to the FIFO\n",len);
		}

		//sem_post()相当于V操作,信号量加1,唤醒等待进程
		sem_post(&full);
		sem_post(&mutex);
	}
	pthread_exit(0);
}

void *customer(void *arg)
{
	unsigned char buf[UNIT_SIZE];
	int len;
	int delay;

	while(time(NULL)<end_time)
	{
		delay = (int)(rand()*DELAY_TIME_LEVELS/(RAND_MAX)/2.0)+1;
		sleep(delay);
		
		sem_wait(&full);
		sem_wait(&mutex);

		printf("\nCustomer: delay = %d\n",delay);
		memset(buf,0,UNIT_SIZE);
		if((len = read(fd,buf,UNIT_SIZE))==-1)
		{
			if(errno==EAGAIN)
			{
				printf("No data yet!\n");
			}
		}
		else
		{
			printf("Read %s from FIFO\n",buf);
		}

		sem_post(&avail);
		sem_post(&mutex);
	}
	pthread_exit(0);
}

int main()
{
	pthread_t pro_id,cus_id;
	int ret;

	srand(time(NULL));
	end_time = time(NULL)+RUN_TIME;

	if(mkfifo(MYFIFO,O_CREAT|O_EXCL)<0 && (errno!=EEXIST))
	{
		printf("Cannot create FIFO\n");
		return errno;
	}

	fd = open(MYFIFO,O_RDWR);
	if(fd==-1)
	{
		printf("Open fifo error!\n");
		return fd;
	}

	ret = sem_init(&mutex,0,1);
	ret += sem_init(&avail,0,BUFFER_SIZE);
	ret += sem_init(&full,0,0);

	if(ret!=0)
	{
		printf("Any semaphore initialization failed\n");
		return ret;
	}

	pthread_create(&pro_id,NULL,producer,NULL);
	pthread_create(&cus_id,NULL,customer,NULL);

	pthread_join(pro_id,NULL);
	pthread_join(cus_id,NULL);
	close(fd);
	//unlink删除的是目录项,将文件链接计数减1,并没有真正的删除文件,可以
	//用来作为临时文件
	unlink(MYFIFO);
}