linux send 阻塞吗

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main() {
    int sockfd;
    struct sockaddr_in serv_addr;
    socklen_t length;

    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        exit(1);
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(8080);

    if (inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
        perror("inet_pton");
        exit(1);
    }

    if (connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
        perror("connect");
        exit(1);
    }

    // 设置非阻塞模式
    int flags = fcntl(sockfd, F_GETFL, 0);
    fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

    const char *message = "Hello, World!";
    int message_len = strlen(message);

    while (1) {
        int sent = send(sockfd, message, message_len, 0);
        if (sent < 0) {
            if (errno == EAGAIN || errno == EWOULDBLOCK) {
                printf("Send buffer is full, retrying...\n");
                sleep(1);
                continue;
            } else {
                perror("send");
                break;
            }
        } else {
            printf("Sent %d bytes\n", sent);
            break;
        }
    }

    close(sockfd);
    return 0;
}