thread互斥测试

编译运行附件中的代码，并说明程序的功能
根据自己的理解，提交不少于3张图片

 

#include  <stdio.h>
#include  <stdlib.h>
#include  <pthread.h>
#include  <ctype.h>

struct arg_set {
		char *fname;
		int  count;
};

struct arg_set  *mailbox = NULL;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;//互斥锁
pthread_cond_t  flag = PTHREAD_COND_INITIALIZER;//条件变量

void *count_words(void *);
int main(int argc, char *argv[])
{
	pthread_t t1, t2;
	struct arg_set args1, args2;	
	int reports_in = 0;
	int	total_words = 0;

	if ( argc != 3 ){
		printf("usage: %s file1 file2
", argv[0]);
		exit(1);
	}

	args1.fname = argv[1];
	args1.count = 0;
	pthread_create(&t1, NULL, count_words, (void *) &args1);

	args2.fname = argv[2];
	args2.count = 0;
	pthread_create(&t2, NULL, count_words, (void *) &args2);

	pthread_mutex_lock(&lock);//拿到互斥锁，进入临界区
	while( reports_in < 2 ){
		printf("MAIN: waiting for flag to go up
");
		pthread_cond_wait(&flag, &lock); //令线程等待在条件变量上
		printf("MAIN: Wow! flag was raised, I have the lock
");
		printf("%7d: %s
", mailbox->count, mailbox->fname);
		total_words += mailbox->count;
		if ( mailbox == &args1) 
			pthread_join(t1,NULL);//等待线程t1执行结束
		if ( mailbox == &args2) 
			pthread_join(t2,NULL);//等待线程t2执行结束
		mailbox = NULL;
		pthread_cond_signal(&flag);	//通知等待在条件变量上的线程
		reports_in++;
	}
	pthread_mutex_unlock(&lock);//释放互斥锁
	
	printf("%7d: total words
", total_words);
}
void *count_words(void *a)
{
	struct arg_set *args = a;
	FILE *fp;
	int  c, prevc = '';
	
	if ( (fp = fopen(args->fname, "r")) != NULL ){
		while( ( c = getc(fp)) != EOF ){
			if ( !isalnum(c) && isalnum(prevc) )
				args->count++;
			prevc = c;
		}
		fclose(fp);
	} else 
		perror(args->fname);
	printf("COUNT: waiting to get lock
");
	pthread_mutex_lock(&lock);//拿到互斥锁，进入临界区	
	printf("COUNT: have lock, storing data
");
	if ( mailbox != NULL ){
		printf("COUNT: oops..mailbox not empty. wait for signal
");
		pthread_cond_wait(&flag,&lock);
	}
	mailbox = args;			
	printf("COUNT: raising flag
");
	pthread_cond_signal(&flag);	//通知等在条件变量上的线程
	printf("COUNT: unlocking box
");
	pthread_mutex_unlock(&lock);	
	return NULL;
}