#include<stdio.h>
#include<string.h>
#include<unistd.h>
#include<stdlib.h>
#include<pthread.h>#define ONE_SECOND 1000000
#define RANGE 10
#define PERIOD 2
#define NUM_THREADS 4typedef struct
{int *carpark;    //用一个数组来模拟停车场停车位int capacity;    //停车场的车辆容量int occupied;    //停车场现有的车辆数目int nextin;        //下一个进来的车的位置（用carpark数组代表的下标表示）int nextout;    //下一个取走的车的停车位置int cars_in;    //记录停车场进入车辆的总和int cars_out;    //记录从停车场开出去的车辆总和pthread_mutex_t lock;    //互斥量，保护该结构中的数据被线程互斥的方式使用pthread_cond_t space;    //条件变量    描述停车场是否有空位置pthread_cond_t car;        //条件变量    描述停车场是否有车pthread_barrier_t bar;    //线程屏障
}cp_t;static void initialise(cp_t *cp,int size)
{cp->occupied = cp->nextin = cp->nextout = cp->cars_in = cp->cars_out = 0;cp->capacity = size;cp->carpark = (int *)malloc(cp->capacity * sizeof(*cp->carpark));//初始化线程屏障，NUM_THREADS表示等待 NUM_THREADS=4个线程同步执行pthread_barrier_init(&cp->bar,NULL,NUM_THREADS);if(cp->carpark == NULL){perror("malloc()");exit(1);}srand((unsigned int )getpid());pthread_mutex_init(&cp->lock,NULL);     //初始化停车场的锁pthread_cond_init(&cp->space,NULL);        //初始化描述停车场是否有空位的条件变量pthread_cond_init(&cp->car,NULL);        //初始化描述停车场是否有车的条件变量
}static void* car_in_handler(void* carpark_in)
{cp_t *temp;unsigned int seed;temp = (cp_t *)carpark_in;//pthread_barrier_wait 函数表示，线程已完成工作，等到其他线程赶来pthread_barrier_wait(&temp->bar);while(1){//将线程挂起一段时间，模拟车辆到来的随机性usleep(rand_r(&seed) % ONE_SECOND);pthread_mutex_lock(&temp->lock);//循环等待知道有停车位while(temp->occupied == temp->capacity)pthread_cond_wait(&temp->space,&temp->lock);//插入一辆车，用随机数标识temp->carpark[temp->nextin] = rand_r(&seed) % RANGE;temp->occupied++;temp->nextin++;temp->nextin %= temp->capacity;temp->cars_in++;//可能有的人在等车可取，发送temp->car条件变量pthread_cond_signal(&temp->car);pthread_mutex_unlock(&temp->lock);}return ((void*)NULL);
}static void* car_out_handler(void *carpark_out)
{cp_t *temp;unsigned int seed;temp = (cp_t *)carpark_out;pthread_barrier_wait(&temp->bar);for(;;){usleep(rand_r(&seed) % ONE_SECOND);pthread_mutex_lock(&temp->lock);/*获得锁后访问temp->occupied 变量，此时如果车辆数为0 （occupied == 0）pthread_cond_wait 进行的操作就是忙等，释放锁(&temp->lock)供其他路线使用知道temp->car条件改变时再次将锁锁住*/while(temp->occupied == 0){pthread_cond_wait(&temp->car,&temp->lock);}temp->occupied--;temp->nextout++;temp->nextout %= temp->capacity;temp->cars_out++;pthread_cond_signal(&temp->space);pthread_mutex_unlock(&temp->lock);}return ((void *)NULL);
}static void *monitor(void *carpark_in)
{cp_t *temp;temp = (cp_t *)carpark_in;for(;;){sleep(PERIOD);pthread_mutex_lock(&temp->lock);printf("Delta:%d\n",temp->cars_in - temp->cars_out - temp->occupied);printf("Number of cars in carpark:%d\n",temp->occupied);pthread_mutex_unlock(&temp->lock);}return ((void *)NULL);
}int main(int argc,char **argv)
{printf("main version 1.0\n");if(argc != 2){printf("Usage :%s carparksize\n",argv[0]);exit(1);}cp_t outpark;initialise(&outpark,atoi(argv[1]));  //初始化停车场数据结构
pthread_t car_in,car_out,m;                //定义线程变量
    pthread_t car_in2,car_out2;/***创建往停车场停车线程（生成者1）创建从停车场取车线程（消费者1）创建往停车场停车线程（生成者2）创建从停车场取车线程（消费者2）创建用于监控停车场状况的线程***/pthread_create(&car_in,NULL,car_in_handler,(void*)&outpark);pthread_create(&car_out,NULL,car_out_handler,(void*)&outpark);pthread_create(&car_in2,NULL,car_in_handler,(void*)&outpark);pthread_create(&car_out2,NULL,car_out_handler,(void*)&outpark);pthread_create(&m,NULL,monitor,(void*)&outpark);//pthread_join的第二个参数为NULL，表示不关心线程返回状态，仅仅等待指定线程的终止
    pthread_join(car_in,NULL);pthread_join(car_out,NULL);pthread_join(car_in2,NULL);pthread_join(car_out2,NULL);pthread_join(m,NULL);return 0;
}