/* twordcount4.c - threaded word counter for two files.	 *		 - Version 4: condition variable allows counter *                            functions to report results early  */#include  <stdio.h>#include  <pthread.h>#include  <ctype.h>struct arg_set {		/* two values in one arg*/		char *fname;	/* file to examine	*/		int  count;	/* number of words	*/};struct arg_set  *mailbox = NULL;pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;pthread_cond_t  flag = PTHREAD_COND_INITIALIZER;main(int ac, char *av[]){	pthread_t      t1, t2;		/* two threads */	struct arg_set args1, args2;	/* two argsets */	void	       *count_words(void *);	int            reports_in = 0;	int	       total_words = 0;	if ( ac != 3 ){		printf("usage: %s file1 file2\n", av[0]);		exit(1);	}	pthread_mutex_lock(&lock);	/* lock the report box now */	args1.fname = av[1];	args1.count = 0;	pthread_create(&t1, NULL, count_words, (void *) &args1);	args2.fname = av[2];	args2.count = 0;	pthread_create(&t2, NULL, count_words, (void *) &args2);	while( reports_in < 2 ){		printf("MAIN: waiting for flag to go up\n");		pthread_cond_wait(&flag, &lock); /* wait for notify */		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);	/* announce state change */		reports_in++;	}	printf("%7d: total words\n", total_words);}void *count_words(void *a){	struct arg_set *args = a;	/* cast arg back to correct type */	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);	/* get the mailbox */	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;			/* put ptr to our args there */	printf("COUNT: raising flag\n");	pthread_cond_signal(&flag);	/* raise the flag */	printf("COUNT: unlocking box\n");	pthread_mutex_unlock(&lock);	/* release the mailbox */	return NULL;}