From 7cd634da51a8d9d93216dd26e6d89e61a4a764ca Mon Sep 17 00:00:00 2001
From: Christian Heller <c.heller@plomlompom.de>
Date: Sat, 29 Apr 2017 02:33:09 +0200
Subject: [PATCH] Improve server by using queues.

---
 server.py | 192 +++++++++++++++++++++++++++++++++---------------------
 1 file changed, 118 insertions(+), 74 deletions(-)

diff --git a/server.py b/server.py
index b088206..82a10a6 100755
--- a/server.py
+++ b/server.py
@@ -4,22 +4,23 @@ import socketserver
 import plom_socket_io
 import threading
 import time
+import queue
 
 # Avoid "Address already in use" errors.
 socketserver.TCPServer.allow_reuse_address = True
 
 
 class Server(socketserver.ThreadingTCPServer):
-    """Bind together threaded IO handling server and world state (counter)."""
+    """Bind together threaded IO handling server and message queue."""
 
-    def __init__(self, counter, *args, **kwargs):
+    def __init__(self, queue, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.counter = counter
+        self.queue_out = queue
         self.daemon_threads = True  # Else, server's threads have daemon=False.
 
 
 def fib(n):
-    """Calculate n-th Fibonacci number."""
+    """Calculate n-th Fibonacci number. Very inefficiently."""
     if n in (1, 2):
         return 1
     else:
@@ -29,10 +30,23 @@ def fib(n):
 class IO_Handler(socketserver.BaseRequestHandler):
 
     def handle(self):
-        """Loop recv for input, send replies; also, send regular counter value.
-
-        If input is 'QUIT', send reply 'BYE' and end loop / connection.
-        Otherwise, use handle_message to interpret and enact commands.
+        """Move messages between network socket and main thread via queues.
+
+        On start, sets up new queue, sends it via self.server.queue_out to
+        main thread, and from then on receives messages to send back from the
+        main thread via that new queue.
+
+        At the same time, loops over socket's recv to get messages from the
+        outside via self.server.queue_out into the main thread. Ends connection
+        once a 'QUIT' message is received from socket, and then also kills its
+        own queue.
+
+        All messages to the main thread are tuples, with the first element a
+        meta command ('ADD_QUEUE' for queue creation, 'KILL_QUEUE' for queue
+        deletion, and 'COMMAND' for everything else), the second element a UUID
+        that uniquely identifies the thread (so that the main thread knows whom
+        to send replies back to), and optionally a third element for further
+        instructions.
         """
         def caught_send(socket, message):
             """Send message by socket, catch broken socket connection error."""
@@ -41,87 +55,117 @@ class IO_Handler(socketserver.BaseRequestHandler):
             except plom_socket_io.BrokenSocketConnection:
                 pass
 
-        def send_counter_loop(socket, counter, kill):
-            """Every 5 seconds, send state of counter[0] until kill[0] set."""
-            while not kill[0]:
-                caught_send(socket, 'COUNTER ' + str(counter[0]))
-                time.sleep(5)
-
-        def handle_message(message):
-            """Evaluate message for tasks to perform, yield result.
-
-            Accepts one command: FIB, followed by positive integers, all tokens
-            separated by whitespace. Will calculate and return for each such
-            integer n the n-th Fibonacci number. Uses multiprocessing to
-            perform multiple such calculations in parallel. Yields a
-            'CALCULATING …' message before the calculation starts, and finally
-            yields a message containing the results. (The 'CALCULATING …'
-            message coming before the results message is currently the main
-            reason this works as a generator function using yield.)
-
-            When no command can be read into the message, just yields a 'NO
-            COMMAND UNDERSTOOD:', followed by the message.
-            """
-            from multiprocessing import Pool
-            tokens = message.split(' ')
-            if tokens[0] == 'FIB':
-                msg_fail_fib = 'MALFORMED FIB REQUEST'
-                if len(tokens) < 2:
-                    yield msg_fail_fib
-                    return
-                numbers = []
-                for token in tokens[1:]:
-                    if token != '0' and token.isdigit():
-                        numbers += [int(token)]
-                    elif token == '':
-                        continue
-                    else:
-                        yield msg_fail_fib
-                        return
-                yield 'CALCULATING …'
-                reply = ''
-                with Pool(len(numbers)) as p:
-                    results = p.map(fib, numbers)
-                reply = ' '.join([str(r) for r in results])
-                yield reply
-                return
-            yield 'NO COMMAND UNDERSTOOD: %s' % message
+        def send_queue_messages(socket, queue_in, thread_alive):
+            """Send messages via socket from queue_in while thread_alive[0]."""
+            while thread_alive[0]:
+                try:
+                    msg = queue_in.get(timeout=1)
+                except queue.Empty:
+                    continue
+                caught_send(socket, msg)
 
+        import uuid
         print('CONNECTION FROM:', str(self.client_address))
-        counter_loop_killer = [False]
-        send_count = threading.Thread(target=send_counter_loop,
-                                      kwargs={'counter': self.server.counter,
-                                              'socket': self.request,
-                                              'kill': counter_loop_killer})
-        send_count.start()
+        connection_id = uuid.uuid4()
+        queue_in = queue.Queue()
+        self.server.queue_out.put(('ADD_QUEUE', connection_id, queue_in))
+        thread_alive = [True]
+        t = threading.Thread(target=send_queue_messages,
+                             args=(self.request, queue_in, thread_alive))
+        t.start()
         for message in plom_socket_io.recv(self.request):
             if message is None:
-                print('RECEIVED MALFORMED MESSAGE')
-                caught_send(self.request, 'bad message')
+                caught_send(self.request, 'BAD MESSAGE')
             elif 'QUIT' == message:
                 caught_send(self.request, 'BYE')
                 break
             else:
-                print('RECEIVED MESSAGE:', message)
-                for reply in handle_message(message):
-                    caught_send(self.request, reply)
-        counter_loop_killer = [True]
+                self.server.queue_out.put(('COMMAND', connection_id, message))
+        self.server.queue_out.put(('KILL_QUEUE', connection_id))
+        thread_alive[0] = False
         print('CONNECTION CLOSED:', str(self.client_address))
         self.request.close()
 
 
-def inc_loop(counter, interval):
-    """Loop incrementing counter every interval seconds."""
+def io_loop(q):
+    """Handle commands coming through queue q, send results back. 
+
+    Commands from q are expected to be tuples, with the first element either
+    'ADD_QUEUE', 'COMMAND', or 'KILL_QUEUE', the second element a UUID, and
+    an optional third element of arbitrary type. The UUID identifies a
+    receiver for replies.
+
+    An 'ADD_QUEUE' command should contain as third element a queue through
+    which to send messages back to the sender of the command. A 'KILL_QUEUE'
+    command removes the queue for that receiver from the list of queues through
+    which to send replies.
+
+    A 'COMMAND' command is specified in greater detail by a string that is the
+    tuple's third element. Here, the following commands are understood:
+    - A string starting with 'PRIVMSG' returns the space-separated tokens
+      following 'PRIVMSG' to the sender via its receiver queue.
+    - A string starting with 'ALL' sends the space-separated tokens following
+      'ALL' to all receiver queues.
+    - A string starting with 'FIB' followed by space-separated positive
+      integers returns to the receiver queue first a 'CALCULATING …' messsage,
+      and afterwards for each such integer n the n-th Fibonacci number as a
+      space-separated sequence of integers. Fibonacci numbers are calculated
+      in parallel if possible.
+    """
+    from multiprocessing import Pool
+    queues_out = {}
     while True:
-        time.sleep(interval)
-        counter[0] += 1
+        x = q.get()
+        command_type = x[0]
+        connection_id = x[1]
+        content = None if len(x) == 2 else x[2]
+        if command_type == 'ADD_QUEUE':
+            queues_out[connection_id] = content
+        elif command_type == 'COMMAND':
+            tokens = [token for token in content.split(' ') if len(token) > 0]
+            if len(tokens) == 0:
+                queues_out[connection_id].put('EMPTY COMMAND')
+                continue
+            if  tokens[0] == 'PRIVMSG':
+                reply = ' '.join(tokens[1:])
+                queues_out[connection_id].put(reply)
+            elif tokens[0] == 'ALL':
+                reply = ' '.join(tokens[1:])
+                for key in queues_out:
+                    queues_out[key].put(reply)
+            elif tokens[0] == 'FIB':
+                fib_fail = 'MALFORMED FIB REQUEST'
+                if len(tokens) < 2:
+                    queues_out[connection_id].put(fib_fail)
+                    continue
+                numbers = []
+                fail = False
+                for token in tokens[1:]:
+                    if token != '0' and token.isdigit():
+                        numbers += [int(token)]
+                    else:
+                        queues_out[connection_id].put(fib_fail)
+                        fail = True
+                        break
+                if fail:
+                    continue
+                queues_out[connection_id].put('CALCULATING …')
+                reply = ''
+                # this blocks the whole loop, BAD
+                with Pool(len(numbers)) as p:
+                    results = p.map(fib, numbers)
+                reply = ' '.join([str(r) for r in results])
+                queues_out[connection_id].put(reply)
+            else:
+                queues_out[connection_id].put('UNKNOWN COMMAND')
+        elif command_type == 'KILL_QUEUE':
+            del queues_out[connection_id]
 
 
-counter = [0]
-b = threading.Thread(target=inc_loop, daemon=True, kwargs={'counter': counter,
-                                                           'interval': 1})
-b.start()
-server = Server(counter, ('localhost', 5000), IO_Handler)
+q = queue.Queue()
+c = threading.Thread(target=io_loop, daemon=True, args=(q,))
+c.start()
+server = Server(q, ('localhost', 5000), IO_Handler)
 try:
     server.serve_forever()
 except KeyboardInterrupt:
-- 
2.30.2