有一個有限緩衝區(這裏用有名管道實現FIFO式緩衝區)和兩個線程:生產者和消費者。它們不停地把產品放入緩衝區和從緩衝區中拿走產品。一個生產者在緩衝區滿的時候必須等待,一個消費者在緩衝區空的時候也必須等待。
信號量的考慮:這裏使用3個信號量avail和full分別用於解決生產者和消費者線程之間的同步問題,mutex是用於這兩個線程之間的互斥問題。其中avail表示有界緩衝區中的空單元數初始值爲N,full表示有界緩衝區非空單元數,初始值爲0;mutex是互斥信號量,初始值爲1。
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<fcntl.h>
#include<pthread.h>
#include<errno.h>
#include<semaphore.h>
#include<sys/ipc.h>
#define MYFIFO "myfifo" //緩衝區有名管道
#define BUFFER_SIZE 3 //緩衝區單元數
#define UNIT_SIZE 5 //每個單元的大小
#define RUN_TIME 30 //運行時間
#define DELAY_TIME_LEVELS 5.0 //週期的最大值
int fd;
time_t end_time;
sem_t mutex,full,avail; //3個信號量
void *producer(void *arg) //生產者線程
{
int real_write;
int delay_time = 0;
while(time(NULL)<end_time)
{
delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)/2.0)+1;
sleep(delay_time);
sem_wait(&avail); //p操作信號量avail和mutex
sem_wait(&mutex);
printf("/nProducer:delay = %d/n",delay_time);
if((real_write = write(fd,"hello",UNIT_SIZE)) == -1) //生產者寫入數據
{
if(errno == EAGAIN)
{
printf("The FIFO has not been read yet.Please try later/n");
}
}
else
{
printf("Write %d to the FIFO/n",real_write);
}
sem_post(&full); //v操作信號量full和mutex
sem_post(&mutex);
}
pthread_exit(NULL);
}
void *customer(void *arg) //消費者線程
{
unsigned char read_buffer[UNIT_SIZE];
int real_read;
int delay_time;
while(time(NULL)<end_time)
{
delay_time = (int)(rand()*DELAY_TIME_LEVELS/(RAND_MAX))+1;
sleep(delay_time);
sem_wait(&full); //p操作信號量full和mutex
sem_wait(&mutex);
memset(read_buffer,0,UNIT_SIZE);
printf("/nCustomer:delay = %d/n",delay_time);
if((real_read = read(fd,read_buffer,UNIT_SIZE)) == -1)
{
if(errno == EAGAIN)
{
printf("No data yet/n");
}
}
printf("Read %s from FIFO/n",read_buffer);
sem_post(&avail); //v操作信號量avail和mutex
sem_post(&mutex);
}
pthread_exit(NULL);
}
int main()
{
pthread_t thrd_prd_id,thrd_cst_id;
pthread_t mon_th_id;
int ret;
srand(time(NULL));
end_time = time(NULL) + RUN_TIME;
if((mkfifo(MYFIFO,O_CREAT|O_EXCL)<0)&&(errno!=EEXIST)) //創建有名管道
{
printf("Cannot create fifo/n");
return errno;
}
fd = open(MYFIFO,O_RDWR); //打開管道
if(fd == -1)
{
printf("Open fifo error/n");
return fd;
}
ret = sem_init(&mutex,0,1); //初始化互斥信號量爲1
ret += sem_init(&avail,0,BUFFER_SIZE); //初始化avail信號量爲n
ret += sem_init(&full,0,0); //初始化full信號量爲0
if(ret != 0)
{
printf("Create producer thread error/n");
return ret;
}
ret = pthread_create(&thrd_prd_id,NULL,producer,NULL); //創建兩個線程
if(ret!=0)
{
printf("Create producer thread error/n");
return ret;
}
ret = pthread_create(&thrd_cst_id,NULL,customer,NULL);
if(ret!=0)
{
printf("Create customer thread error/n");
return ret;
}
pthread_join(thrd_prd_id,NULL);
pthread_join(thrd_cst_id,NULL);
close(fd);
unlink(MYFIFO);
return 0;
}