Strange behavior of python socket in docker container

问题

I observed a behavior of my python code running in a docker container I don't understand. Maybe someone can explain me the behavior and can me tell the difference between python socket on Ubuntu 18.04 and the docker image python:3.6

If I start my UDP socket at my host the server thread unblock on every received datagram and print the bytes out. That is the behavior I expect.

If I start the same code in docker container, there is no unblocking and no output to stdout. If a stop the server with ctrl+c the output is printed before the interrupt exception.

UPDATE

Add a example for a thread printing out to stdout without any problems. See I/O Test.
Add code to show the the ininstantiating of the objects and the start() call.
Add Docker run commands. Start the container and print out stdout.
Remove unnecessary print() output.

Thanks and enjoy my creepy code!

Dockerfile: Server

FROM python:3.6

COPY . /workdir
EXPOSE 8888
WORKDIR /workdir
CMD ["./main.py"]

Dockerfile: I/O Test

FROM python:3.6

COPY . /workdir
EXPOSE 8888
WORKDIR /workdir
CMD ["./iotest.py"]

I/O test (same as UDPServer but without blocking socket) *

import threading

    class iotest(threading.Thread):

        def __init__(self):
            threading.Thread.__init__(self)

        def run(self):
            print("Server Thread started!")
            try:
                while True:
                    print("Test i/o")
            except Exception as e:
                print("Exception catched")
                print(e)
            finally:
                print("Thread exited")

Server:

import threading
import socket


class UDPServer(threading.Thread):
    PORT = 8888
    HOST = '0.0.0.0'

    def __init__(self):
        threading.Thread.__init__(self)

    def run(self):
        print("Server Thread started!")
        try:
            s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
            s.bind((UDPServer.HOST, UDPServer.PORT))
            while True:
                msg = s.recv(4)
                print("Message received")
        except Exception as e:
            print("Exception catched")
            print(e)
        finally:
            print("Thread exited, Socket closed")
            s.close()

I/O test (same as UDPServer but without blocking socket) *

import threading

    class iotest(threading.Thread):

        def __init__(self):
            threading.Thread.__init__(self)

        def run(self):
            print("Server Thread started!")
            try:
                while True:
                    print("Test i/o")
            except Exception as e:
                print("Exception catched")
                print(e)
            finally:
                print("Thread exited")

Client:

import socket
import time

s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.connect(('0.0.0.0', 8888))
count = 0
errors = 0
for i in range(10):
    isTime = time.time()
    msg = struct.pack('!f', isTime, )
    time.sleep(0.5)
    try:
        size_date_sent = s.send(msg)
        count += 1
    except Exception as identifier:
        errors += 1

print(str(count) + " MSG sent.")
print(str(errors) + " errors.")
s.close()

main.py:

import UDPServer

server = UDPServer.UDPServer()
server.start()

iotest.py

import iotest

thr = iotest.iotest()
thr.start

Build and run

docker build -t pythontest .
docker run -p 8888:8888/udp pythontest

来源：https://stackoverflow.com/questions/54990469/strange-behavior-of-python-socket-in-docker-container

标签

python

sockets

Docker

udp