经典同步问题linux下的C实现：生产者-消费者问题，读者-写者问题，哲学家问题

1.生产者-消费者问题

/*=============================================================== * File Name : producerConsumerProblem.c * Creation Date : 2013-04-11 * Last Modified : 2013年04月11日 星期四 20时53分13秒 * Purpose :test linux semaphore usage================================================================*/#include <stdio.h>#include <sys/types.h>#include <semaphore.h>#include <pthread.h>#include <stdlib.h>void *producer_handler(void *ptr);void *consumer_handler(void *ptr);sem_t mutex,blank,fill;int *buffer;int in=0,out=0,buffer_size=10;void main(){if((buffer=(int *)malloc(buffer_size*sizeof(int)))==NULL)printf("can't allocate memroy on heap\n");sem_init(&mutex,0,1);sem_init(&blank,0,buffer_size);sem_init(&fill,0,0);int err;pthread_t producer,consumer;err=pthread_create(&producer,NULL,producer_handler,NULL);if(err!=0)err_quit("can't create thread: %s\n",strerror(err));err=pthread_create(&consumer,NULL,consumer_handler,NULL);if(err!=0)err_quit("can't create thread: %s\n",strerror(err));sleep(10);}void *producer_handler(void *ptr){while(1){static int data=0;sem_wait(&blank);//sem_wait(&mutex);buffer[in]=++data;printf("%d has been input to the buffer\n",data);in=(in+1+buffer_size)%buffer_size;//sem_post(&mutex);sem_post(&fill);sleep(1);}return ((void *)0);}void *consumer_handler(void *ptr){while(1){int fetch;sem_wait(&fill);//sem_wait(&mutex);fetch=buffer[out];out=(out+1+buffer_size)%buffer_size;printf("%d has been fetched\n",fetch);//sem_post(&mutex);sem_post(&blank);sleep(2);}return ((void *)0);}

2.读者-写者问题

/*=============================================================== * File Name : readerWriterProblem.c * Creation Date : 2013-04-11 * Last Modified : 2013年04月11日 星期四 22时42分45秒 * Purpose :================================================================*/#include <stdio.h>#include <sys/types.h>#include <semaphore.h>#include <pthread.h>#include <stdlib.h>#define READER_NUM 5void *reader_handler(void *ptr);void *writer_handler(void *ptr);sem_t write_mutex;sem_t mutex;int read_count;void main(){sem_init(&write_mutex,0,1);sem_init(&mutex,0,1);read_count=0;int err,i;pthread_t reader[READER_NUM],writer;int args[READER_NUM];for(i=0;i<READER_NUM;++i){args[i]=i;err=pthread_create(&reader[i],NULL,reader_handler,(void*)&args[i]);if(err!=0)err_quit("can't create thread: %s\n",strerror(err));}err=pthread_create(&writer,NULL,writer_handler,NULL);if(err!=0)err_quit("can't create thread: %s\n",strerror(err));sleep(10);}void *reader_handler(void *ptr){while(1){if(read_count==0){sem_wait(&write_mutex);}sem_wait(&mutex);++read_count;sem_post(&mutex);printf("There are %d readers reading\n",read_count);sleep(1);sem_wait(&mutex);--read_count;sem_post(&mutex);if(read_count==0){sem_post(&write_mutex);}sleep(1);}return ((void *)0);}void *writer_handler(void *ptr){while(1){if(read_count==0){sem_wait(&write_mutex);printf("Writer writes\n");sem_post(&write_mutex);}elseprintf("Writer failed\n");sleep(1);}return ((void *)0);}

3.哲学家进餐问题

有一点要注意：

        就是循环生生成线程时，要给线程处理函数传入计数器参数时，不能直接用计数器的地址——因为计数器会现在主函数中改变。显然也不能用循环中的临时变量来记录。所以只好再有外部数组来记录这些实参值了。

/*=============================================================== * File Name : dinningPhilosophersProblem.c * Creation Date : 2013-04-11 * Last Modified : 2013年04月11日 星期四 21时34分18秒 * Purpose :================================================================*/#include <stdio.h>#include <sys/types.h>#include <semaphore.h>#include <pthread.h>#include <stdlib.h>#define PHILO_NUM 5void *philosopher(void *arg);sem_t sema[PHILO_NUM];sem_t mutex;void main(){int i,err;int args[PHILO_NUM];for(i=0;i<PHILO_NUM;++i){sem_init(sema+i,0,1);args[i]=i;}  sem_init(&mutex,0,1);pthread_t philosophers[PHILO_NUM];for(i=0;i<PHILO_NUM;++i){err=pthread_create(philosophers+i,NULL,philosopher,(void*)&args[i]);if(err!=0)err_quit("can't create thread: %s\n",strerror(err));}sleep(5);}void *philosopher(void *arg){int num;num=*((int *)arg);//printf("Philosopher %d eats\n",num);while(1){sem_wait(&mutex); sem_wait(&sema[num]);sem_wait(&sema[(num+1)%PHILO_NUM]);sem_post(&mutex);printf("Philosopher %d eats\n",num);sem_post(&sema[num]);sem_post(&(sema[(num+1)%PHILO_NUM]));sleep(1);}return ((void *)0);}