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

 

代码： 

#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;
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 ", 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 ");
pthread_cond_wait(&flag, &lock);
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);
if ( mailbox == &args2)
pthread_join(t2,NULL);
mailbox = NULL;
pthread_cond_signal(&flag);
reports_in++;
}
pthread_mutex_unlock(&lock);

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);
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);
printf("COUNT: unlocking box ");
pthread_mutex_unlock(&lock);
return NULL;
}