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

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#include  
#include  
#include  
#include  
struct arg_set {

char *fname;

int  count;

};
struct arg_set  *mailbox = NULL;

pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

pthread_cond_t  flag = PTHREAD_COND_INITIALIZER;
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\n", 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);
while( reports_in < 2 ){
	printf("MAIN: waiting for flag to go up\n");
	pthread_cond_wait(&flag, &lock); 
	printf("MAIN: Wow! flag was raised, I have the lock\n");
	printf("%7d: %s\n", mailbox->count, mailbox->fname);
	total_words += mailbox->count;
	if ( mailbox == &args1) 
		pthread_join(t1,NULL);
	if ( mailbox == &args2) 
		pthread_join(t2,NULL);
	mailbox = NULL;
	pthread_cond_signal(&flag);	
	reports_in++;
}
pthread_mutex_unlock(&lock);

printf("%7d: total words\n", total_words);

}

void *count_words(void *a)

{

struct arg_set *args = a;

FILE *fp;

int  c, prevc = '\0';
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\n");
pthread_mutex_lock(&lock);	
printf("COUNT: have lock, storing data\n");
if ( mailbox != NULL ){
	printf("COUNT: oops..mailbox not empty. wait for signal\n");
	pthread_cond_wait(&flag,&lock);
}
mailbox = args;			
printf("COUNT: raising flag\n");
pthread_cond_signal(&flag);	
printf("COUNT: unlocking box\n");
pthread_mutex_unlock(&lock);	
return NULL;

}

• 编译：
  

• 运行结果：
  

该代码实现了一个线程互斥，创建一个互斥锁，并对线程进行加锁解锁，通过flag参数来决定是否unlock，没有得到flag的线程处于等待队列，得到lock的线程先执行。

• 使用命令wc file1 file2的运行结果：
  

wc命令用来计算一个文件或者指定的多个文件中的行数，单词数和字符数。
如：wc filename，第一列显示行数，第二列显示单词数，第三列显示字符数。