linux 多线程 读文件

#include <pthread.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>

#define NUM_THREADS 4

typedef struct {
    int thread_id;
    off_t offset;
    size_t length;
} thread_data_t;

int file_descriptor;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void* read_file(void* arg) {
    thread_data_t* data = (thread_data_t*)arg;
    char buffer[data->length];
    pthread_mutex_lock(&mutex);
    lseek(file_descriptor, data->offset, SEEK_SET);
    read(file_descriptor, buffer, data->length);
    pthread_mutex_unlock(&mutex);
    // 处理读取的数据
    printf("Thread %d read data from offset %ld\n", data->thread_id, data->offset);
    return NULL;
}

int main() {
    file_descriptor = open("example.txt", O_RDONLY);
    if (file_descriptor < 0) {
        perror("open");
        return 1;
    }

    pthread_t threads[NUM_THREADS];
    thread_data_t thread_data[NUM_THREADS];
    off_t file_size = lseek(file_descriptor, 0, SEEK_END);
    size_t chunk_size = file_size / NUM_THREADS;

    for (int i = 0; i < NUM_THREADS; ++i) {
        thread_data[i].thread_id = i;
        thread_data[i].offset = i * chunk_size;
        thread_data[i].length = (i == NUM_THREADS - 1) ? (file_size - i * chunk_size) : chunk_size;
        pthread_create(&threads[i], NULL, read_file, &thread_data[i]);
    }

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

    close(file_descriptor);
    return 0;
}