java用信号量写理发师

java用信号量写理发师

理发店里有一位理发师、一把理发椅和n把供等候理发的顾客坐的椅子。如果没有顾客，理发师在理发椅上睡觉。一个顾客来到时，叫醒理发师，如果理发师正在理发时有顾客到来，则如果有空椅子可以坐，就坐下来等待，否则离开。

利用三个信号量和一个控制变量来协调理发师、理发椅和顾客之间的活动。

1.信号量customers 用来记录等候理发的顾客数，并用坐阻塞理发师进程，初值为0

2.信号量barbers 记录正在等候顾客的理发师数

3.信号量waiting 用来记录等候理发的顾客数

4.信号量mutex 用于互斥，初值为1

/*基于信号量采用多线程技术实现进程同步*/

#include

#include

#include

#include

#include

#include

#include

#define CHAIRS 5 //椅子数

sem_t customers; //等待服务的顾客信号量

sem_t barbers; //等待顾客的理发师信号量

pthread_mutex_t mutex; //互斥变量

int waiting = 0; //正在等待的顾客数

void *barber(void *arg);

void *customer(void *num);

void cut_hair(void);

double timediff(struct timeval i,struct timeval j);

void seed_random(void);

double flat(void);

double normal(void);

double bursty(void);

int main()

{

int i;

seed_random();

pthread_t barber_t,customer_t;

int error;

error=pthread_create(&barber_t,NULL,barber,NULL);//创建理发师线程

if(error!=0) {

printf("pthread_create is /n");

return -1;

}

while(1) {

usleep(30000);//等待时间如果小于理发师理发时间则会出现等待者过多,否则不会出现等待者过多的现象

error=pthread_create(&customer_t,NULL,customer,NULL);//创建顾客线程

if(error!=0) {

printf("pthread_create is /n");

return -1;

}

}

}

double timediff(struct timeval now,struct timeval earlier)

{

if(now.tv_sec == earlier.tv_sec)

return (now.tv_usec - earlier.tv_usec)/1000000.0;

else

return (1000000*(now.tv_sec - earlier.tv_sec) + now.tv_usec - earlier.tv_usec)/1000000.0;

}

void *barber(void *arg)

{

while(1)

{

sem_wait(&customers);//顾客信号量-1

pthread_mutex_lock(&mutex);

waiting = waiting -1;

sem_post(&barbers);//

pthread_mutex_unlock(&mutex);

cut_hair();//理发

}

}

void cut_hair(void)

{

printf(" Barber:I am cutting the customer'/n");

usleep(100000);//理发时间

printf(" Barber:done./n");

}

void *customer(void *num)

{

pthread_mutex_lock(&mutex);

if(waiting

{

waiting = waiting + 1;

sem_post(&customers);

pthread_mutex_unlock(&mutex);

sem_wait(&barbers);

}

else

{

printf(" Waiter is /n");

pthread_mutex_unlock(&mutex);

}

//释放占用的资源

}

void seed_random(void)

{

struct timeval randtime;

unsigned short xsub1[3];

gettimeofday(&randtime,(struct timezone *)0);

xsub1[0] = (ushort)randtime.tv_usec;

xsub1[1] = (ushort)(randtime.tv_usec >> 16);

xsub1[2] = (ushort)(getpid());

seed48(xsub1);

}

double flat()

{

return drand48()/5;

}