linux 阻塞进程

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

int main() {
    int fd = open("test.txt", O_RDONLY);
    if (fd == -1) {
        perror("open");
        exit(1);
    }

    // 阻塞I/O
    char buffer[1024];
    ssize_t n = read(fd, buffer, sizeof(buffer));
    if (n == -1) {
        perror("read");
        close(fd);
        exit(1);
    }
    buffer[n] = '\0';
    printf("Read: %s\n", buffer);

    // 非阻塞I/O
    int flags = fcntl(fd, F_GETFL, 0);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);

    n = read(fd, buffer, sizeof(buffer));
    if (n == -1) {
        if (errno == EAGAIN || errno == EWOULDBLOCK) {
            printf("No data available yet\n");
        } else {
            perror("read");
        }
    } else {
        buffer[n] = '\0';
        printf("Read: %s\n", buffer);
    }

    close(fd);
    return 0;
}