example_shutdown.py

"""Example of waiting on a socket or a shutdown signal."""
import threading
import time
import socket
import json


def main():
    """Main thread, which spawns a second server() thread."""
    print("main() starting")
    signals = {"shutdown": False}
    thread = threading.Thread(target=server, args=(signals,))
    thread.start()
    time.sleep(10)  # Give up execution to the 'server' thread (see Pitfall 1)
    signals["shutdown"] = True  # Tell server thread to shut down
    thread.join()  # Wait for server thread to shut down
    print("main() shutting down")


def server(signals):
    """Wait on a message from a socket OR a shutdown signal."""
    print("server() starting")
    # Create an INET, STREAMing socket, this is TCP
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
        # Bind the socket to the server
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sock.bind(("localhost", 8000))
        sock.listen()
        # Socket accept() will block for a maximum of 1 second.  If you
        # omit this, it blocks indefinitely, waiting for a connection.
        sock.settimeout(1)
        while not signals["shutdown"]:
            print("waiting ...")
            # Wait for a connection for 1s.  The socket library avoids
            # consuming CPU while waiting for a connection.
            try:
                clientsocket, address = sock.accept()
            except socket.timeout:
                continue
            print("Connection from", address[0])
            # Socket recv() will block for a maximum of 1 second.  If you omit
            # this, it blocks indefinitely, waiting for packets.
            clientsocket.settimeout(1)
            # Receive data, one chunk at a time.  If recv() times out before
            # we can read a chunk, then go back to the top of the loop and try
            # again.  When the client closes the connection, recv() returns
            # empty data, which breaks out of the loop.  We make a simplifying
            # assumption that the client will always cleanly close the
            # connection.
            with clientsocket:
                message_chunks = []
                while True:
                    try:
                        data = clientsocket.recv(4096)
                    except socket.timeout:
                        continue
                    if not data:
                        break
                    message_chunks.append(data)
            # Decode list-of-byte-strings to UTF8 and parse JSON data
            message_bytes = b''.join(message_chunks)
            message_str = message_bytes.decode("utf-8")
            try:
                message_dict = json.loads(message_str)
            except json.JSONDecodeError:
                continue
            print(message_dict)
    print("server() shutting down")


if __name__ == "__main__":
    main()