Question

这里的想法是创建一个要写入的文件。我试图创建十个线程并让它们分别打印到文件10次。使用信号量可以阻止多个线程一次写入文件。但我有错误。代码如下：

#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>

#define FNAME   "fisier.txt"
#define MAX_STRING_LEN  80
#define NUMBER_OF_THREADS 10

FILE *fp;
sem_t mutex;
int counter;

FILE *makeTextFile(char *fname, char mode){
   FILE *localFP;
   localFP = fopen(fname, &mode);
 return (localFP);
}

void *print_message(void *tid){
    int i;
    for (i = 0; i < 10; i++){
        sem_wait(&mutex);
        fp = fopen(FNAME, "a");
        fprintf(fp, "Thread %d is running.\n", tid);
        fclose(fp);
    sem_post(&mutex);
    printf ( "Thread %d has finished.\n", tid);
    }
}

int threads(){
    const char *fName = "fisier.txt";
    int status;
    pthread_t threads[NUMBER_OF_THREADS];
    fp = makeTextFile(FNAME, 'w');
    fprintf(fp, "Process ID: %ld\n", (long)getpid());
    fclose(fp);

    int i;
    for (i =0; i < NUMBER_OF_THREADS; i++){
        status = pthread_create(&threads[i], NULL, &print_message, (void *)i);
        if (status != 0){
            printf("pthread_create returned error code %d\n", status);
            exit(-1);
        }
     }
    }

int main() {
    threads();  

    return 0;
}

警告：

probl2.c: In function ‘print_message’:
probl2.c:27:21: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘void *’ [-Wformat=]
         fprintf(fp, "Thread %d is running.\n", tid);
                     ^
probl2.c:30:14: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘void *’ [-Wformat=]
     printf ( "Thread %d has finished.\n", tid);
              ^
probl2.c: In function ‘threads’:
probl2.c:44:68: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
   status = pthread_create(&threads[i], NULL, &print_message, (void *)i);

仅在文件中写入：进程ID：10568 我想写怎么解决？

Answer 1

我发现了一些事情：

您没有初始化您的信号量。使用 sem_init 执行此操作（并在完成后使用 sem_destroy ）。

您没有加入自己的主题。程序将退出而不等待线程完成。您可以在循环中使用 pthread_join 来确保所有线程都已完成。

这是您的线程功能的更新版本。在生产代码中，我会检查我添加的函数的返回值。

void threads(){
    const char *fName = "fisier.txt";
    int status;
    pthread_t threads[NUMBER_OF_THREADS];
    fp = makeTextFile(FNAME, 'w');
    fprintf(fp, "Process ID: %ld\n", (long)getpid());
    fclose(fp);

    sem_init(&mutex,0,1);
    int i;

    for (i =0; i < NUMBER_OF_THREADS; i++){
        status = pthread_create(&threads[i], NULL, &print_message, (void*)i);
        if (status != 0){
            printf("pthread_create returned error code %d\n", status);
            exit(-1);
        }
     }

     void* value = NULL;
     for (i = 0; i < NUMBER_OF_THREADS; i++) {
         pthread_join(threads[i], &value);
     }
     sem_destroy(&mutex);
}

使用20个线程写入文件

1 个答案: