从通过socketpair创建的套接字接收消息时，可能会丢失数据吗？

Question

下面是我的代码示例，我派生了一个新进程，并使用它通过主进程发送的UDS接收消息，但我在子进程的逻辑中添加了一个time.sleep(5)：

import os
import socket
import threading
import time


def read_content_from_parent_socket(socket):
    while True:
        try:
            result = socket.recv(4096)
            if not result:
                continue
            print("[In threading]: Get response: %s from child." % result)
        except socket.timeout:
            pass


def handle_request_in_method(socket, result):
    print("[In Process]started to execute method, %s. at time: %s" % (result.split(",")[-1], time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())))
    message = ("[In Process]: Response from child at time: %s, %s" % (
    time.strftime("%Y-%m-%d %H:%M:%S", time.localtime()),
    result.split(",")[-1]))
    socket.sendall(message)


def receive_and_reply_to_parent_socket(socket):
    while True:
        try:
            time.sleep(5)
            result = socket.recv(4096)
        except socket.timeout:
            pass
        except Exception:
            pass
        handle_request_in_method(socket, result)


def main():
    # Setup the socket pair
    socket_parent, socket_child = socket.socketpair()
    socket_child.setblocking(True)
    socket_parent.setblocking(True)
    # Listen to the parent socket via thread
    listening_socket = threading.Thread(target=read_content_from_parent_socket, args=(socket_parent, ))
    listening_socket.start()
    p_id = os.fork()
    if p_id == 0:
        socket_parent.close()
        receive_and_reply_to_parent_socket(socket_child)
    # This is in parent process
    # Send Ping recursively every one seconds.
    message_count = 0
    socket_child.close()
    while True:
        time.sleep(1)
        message_count += 1
        message = "[Main process]: Request from parent at time: %s, %s" % (time.strftime("%Y-%m-%d %H:%M:%S", time.localtime()), message_count)
        print(message)
        socket_parent.sendall(message)


if __name__ == "__main__":
    main()

然后，我们可以发现日志中缺少一些消息：

[Main process]: Request from parent at time: 2018-08-20 15:54:43, 1
[Main process]: Request from parent at time: 2018-08-20 15:54:44, 2
[Main process]: Request from parent at time: 2018-08-20 15:54:45, 3
[Main process]: Request from parent at time: 2018-08-20 15:54:46, 4
[In Process]started to execute method,  4. at time: 2018-08-20 15:54:47
[In threading]: Get response: [In Process]: Response from child at time: 2018-08-20 15:54:47,  4 from child.

为什么会发生这种情况？缺少的消息1、2和3在哪里？

Answer 1

您可以打印子进程在没有split(',')的情况下接收到的内容

[Main process]: Request from parent at time: 2018-08-20 16:22:53, 1[Main process]: Request from parent at time: 2018-08-20 16:22:54, 2[Main process]: Request from parent at time: 2018-08-20 16:22:55, 3[Main process]: Request from parent at time: 2018-08-20 16:22:56, 4

如果您使用TCP处理上面的字符串，您将得到4，但不会遗漏任何消息，因为sockerpair默认使用TCP。