linux c多线程读写文件

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

#define NUM_THREADS 4

pthread_mutex_t mutex;
FILE *file;

void* write_to_file(void* thread_id) {
    long tid = (long)thread_id;
    char buffer[256];

    pthread_mutex_lock(&mutex);
    sprintf(buffer, "Thread %ld writing to file\n", tid);
    fputs(buffer, file);
    pthread_mutex_unlock(&mutex);

    pthread_exit(NULL);
}

int main() {
    pthread_t threads[NUM_THREADS];
    int rc;
    long t;

    file = fopen("output.txt", "w");
    if (file == NULL) {
        perror("Error opening file");
        exit(1);
    }

    pthread_mutex_init(&mutex, NULL);

    for (t = 0; t < NUM_THREADS; t++) {
        rc = pthread_create(&threads[t], NULL, write_to_file, (void*)t);
        if (rc) {
            perror("Error creating thread");
            exit(1);
        }
    }

    for (t = 0; t < NUM_THREADS; t++) {
        pthread_join(threads[t], NULL);
    }

    fclose(file);
    pthread_mutex_destroy(&mutex);

    return 0;
}