Refactor the replies waiter code

This changes improves the way of we wait for replies.
Currently, one of the rpc client is reponsible to poll the amqp connection
used for replies and passed received answers to the correct client.

In this way, we have some case if no client is waiting for a reply, the
connection is not polled and no IO are done on the wire. The direct
effect of that is we don't detect if the tcp connection is broken,
from the system point of view, the tcp connection stay alive even if someone
between the client and server have closed the connection.

This change refactors the replies waiter code by creating a background
thread responsible to poll the connection instead of a random client.
The connection lost will be detect as soon as possible even if no rpc
client are currently used the connection.

This is a mandatory change to be able to enable heartbeat on this
connection.

Related-Bug: #1371723
Related-Bug: #856764

Change-Id: I82d4029dd897ef13ae8ba3cda84a2fe65c8c91d2

oslo_messaging/_drivers/amqpdriver.py

@@ -147,12 +147,6 @@ class ReplyWaiters(object):
                 'Timed out waiting for a reply '
                 'to message ID %s' % msg_id)
 
-    def check(self, msg_id):
-        try:
-            return self._queues[msg_id].get(block=False)
-        except moves.queue.Empty:
-            return None
-
     def put(self, msg_id, message_data):
         queue = self._queues.get(msg_id)
         if not queue:
@@ -162,13 +156,8 @@ class ReplyWaiters(object):
         else:
             queue.put(message_data)
 
-    def wake_all(self, except_id):
-        msg_ids = [i for i in self._queues.keys() if i != except_id]
-        for msg_id in msg_ids:
-            self.put(msg_id, self.WAKE_UP)
-
-    def add(self, msg_id, queue):
-        self._queues[msg_id] = queue
+    def add(self, msg_id):
+        self._queues[msg_id] = moves.queue.Queue()
         if len(self._queues) > self._wrn_threshold:
             LOG.warn('Number of call queues is greater than warning '
                      'threshold: %d. There could be a leak. Increasing'
@@ -181,27 +170,41 @@ class ReplyWaiters(object):
 
 
 class ReplyWaiter(object):
-
-    def __init__(self, conf, reply_q, conn, allowed_remote_exmods):
-        self.conf = conf
+    def __init__(self, reply_q, conn, allowed_remote_exmods):
         self.conn = conn
-        self.reply_q = reply_q
         self.allowed_remote_exmods = allowed_remote_exmods
-
-        self.conn_lock = threading.Lock()
-        self.incoming = []
         self.msg_id_cache = rpc_amqp._MsgIdCache()
         self.waiters = ReplyWaiters()
 
-        conn.declare_direct_consumer(reply_q, self)
+        self.conn.declare_direct_consumer(reply_q, self)
+
+        self._thread_exit_event = threading.Event()
+        self._thread = threading.Thread(target=self.poll)
+        self._thread.daemon = True
+        self._thread.start()
+
+    def stop(self):
+        if self._thread:
+            self._thread_exit_event.set()
+            self.conn.stop_consuming()
+            self._thread.join()
+            self._thread = None
+
+    def poll(self):
+        while not self._thread_exit_event.is_set():
+            try:
+                self.conn.consume(limit=1)
+            except Exception:
+                LOG.exception("Failed to process incoming message, "
+                              "retrying...")
 
     def __call__(self, message):
         message.acknowledge()
-        self.incoming.append(message)
+        incoming_msg_id = message.pop('_msg_id', None)
+        self.waiters.put(incoming_msg_id, message)
 
     def listen(self, msg_id):
-        queue = moves.queue.Queue()
-        self.waiters.add(msg_id, queue)
+        self.waiters.add(msg_id)
 
     def unlisten(self, msg_id):
         self.waiters.remove(msg_id)
@@ -225,96 +228,25 @@ class ReplyWaiter(object):
             result = data['result']
         return result, ending
 
-    def _poll_connection(self, msg_id, timer):
-        while True:
-            while self.incoming:
-                message_data = self.incoming.pop(0)
-
-                incoming_msg_id = message_data.pop('_msg_id', None)
-                if incoming_msg_id == msg_id:
-                    return self._process_reply(message_data)
-
-                self.waiters.put(incoming_msg_id, message_data)
-
+    def wait(self, msg_id, timeout):
+        # NOTE(sileht): for each msg_id we receive two amqp message
+        # first one with the payload, a second one to ensure the other
+        # have finish to send the payload
+        timer = rpc_common.DecayingTimer(duration=timeout)
+        timer.start()
+        final_reply = None
+        ending = False
+        while not ending:
             timeout = timer.check_return(self._raise_timeout_exception, msg_id)
             try:
-                self.conn.consume(limit=1, timeout=timeout)
-            except rpc_common.Timeout:
+                message = self.waiters.get(msg_id, timeout=timeout)
+            except moves.queue.Empty:
                 self._raise_timeout_exception(msg_id)
 
-    def _poll_queue(self, msg_id, timer):
-        timeout = timer.check_return(self._raise_timeout_exception, msg_id)
-        message = self.waiters.get(msg_id, timeout=timeout)
-        if message is self.waiters.WAKE_UP:
-            return None, None, True  # lock was released
-
-        reply, ending = self._process_reply(message)
-        return reply, ending, False
-
-    def _check_queue(self, msg_id):
-        while True:
-            message = self.waiters.check(msg_id)
-            if message is self.waiters.WAKE_UP:
-                continue
-            if message is None:
-                return None, None, True  # queue is empty
-
             reply, ending = self._process_reply(message)
-            return reply, ending, False
-
-    def wait(self, msg_id, timeout):
-        #
-        # NOTE(markmc): we're waiting for a reply for msg_id to come in for on
-        # the reply_q, but there may be other threads also waiting for replies
-        # to other msg_ids
-        #
-        # Only one thread can be consuming from the queue using this connection
-        # and we don't want to hold open a connection per thread, so instead we
-        # have the first thread take responsibility for passing replies not
-        # intended for itself to the appropriate thread.
-        #
-        timer = rpc_common.DecayingTimer(duration=timeout)
-        timer.start()
-        final_reply = None
-        while True:
-            if self.conn_lock.acquire(False):
-                # Ok, we're the thread responsible for polling the connection
-                try:
-                    # Check the queue to see if a previous lock-holding thread
-                    # queued up a reply already
-                    while True:
-                        reply, ending, empty = self._check_queue(msg_id)
-                        if empty:
-                            break
-                        if not ending:
-                            final_reply = reply
-                        else:
-                            return final_reply
-
-                    # Now actually poll the connection
-                    while True:
-                        reply, ending = self._poll_connection(msg_id, timer)
-                        if not ending:
-                            final_reply = reply
-                        else:
-                            return final_reply
-                finally:
-                    self.conn_lock.release()
-                    # We've got our reply, tell the other threads to wake up
-                    # so that one of them will take over the responsibility for
-                    # polling the connection
-                    self.waiters.wake_all(msg_id)
-            else:
-                # We're going to wait for the first thread to pass us our reply
-                reply, ending, trylock = self._poll_queue(msg_id, timer)
-                if trylock:
-                    # The first thread got its reply, let's try and take over
-                    # the responsibility for polling
-                    continue
-                if not ending:
-                    final_reply = reply
-                else:
-                    return final_reply
+            if not ending:
+                final_reply = reply
+        return final_reply
 
 
 class AMQPDriverBase(base.BaseDriver):
@@ -349,7 +281,7 @@ class AMQPDriverBase(base.BaseDriver):
 
             conn = self._get_connection(pooled=False)
 
-            self._waiter = ReplyWaiter(self.conf, reply_q, conn,
+            self._waiter = ReplyWaiter(reply_q, conn,
                                        self._allowed_remote_exmods)
 
             self._reply_q = reply_q
@@ -451,3 +383,11 @@ class AMQPDriverBase(base.BaseDriver):
         if self._connection_pool:
             self._connection_pool.empty()
         self._connection_pool = None
+
+        with self._reply_q_lock:
+            if self._reply_q is not None:
+                self._waiter.stop()
+                self._reply_q_conn.close()
+                self._reply_q_conn = None
+                self._reply_q = None
+                self._waiter = None