thread互斥
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#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\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 ); //拿到互斥锁,进入临界区 while ( reports_in < 2 ){ printf( "MAIN: waiting for flag to go up\n" ); 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\n" ); printf( "%7d: %s\n" , 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\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 ); //拿到互斥锁,进入临界区 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); //通知等在条件变量上的线程 printf( "COUNT: unlocking box\n" ); pthread_mutex_unlock(& lock ); return NULL; } |