Fixes #151: Send messages only when there is credit to send instead o… (

#1282)

* Fixes #151: Send messages only when there is credit to send instead of sending all messages in one single loop. This makes sure that we are not exhausting credit inside the send loop

* Python checker errors

tests/system_tests_delivery_counts.py

@@ -875,6 +875,9 @@ def __init__(self, router_addr, count=None, rx_limit=None,
             self.receiver = None
             self.max_attempts = 10
             self.num_attempts = 0
+            self.poll_timer_started = False
+            self.n_accepted = 0
+            self.n_released = 0
 
         def timeout(self):
             self._cleanup()
@@ -935,7 +938,9 @@ def on_start(self, event):
                                                         name="Tx_Test01")
 
         def on_sendable(self, event):
-            while self.sent < self.count:
+            # Don't send all messages in one single loop.
+            # on_sendable is called only when there is credit, so send a message when there is credit.
+            if self.sent < self.count:
                 if self.large_message:
                     dlv = self.sender.send(Message(body=LARGE_PAYLOAD))
                 else:
@@ -944,19 +949,37 @@ def on_sendable(self, event):
                     dlv.settle()
                 self.sent += 1
 
+                # Start up a poll timer once all the deliveries have been sent/received.
+                if self.received == self.rx_limit and self.sent == self.count and not self.poll_timer_started and self.outcome is None:
+                    self.poll_timer_started = True
+                    self.poll_timer = event.reactor.schedule(0.5, PollTimeout(self))
+
         def on_message(self, event):
             self.received += 1
             if self.outcome:
                 event.delivery.update(self.outcome)
                 event.delivery.settle()
 
             # Start up a poll timer once all the deliveries have been sent/received.
-            if self.received == self.rx_limit and self.sent ==  self.count:
+            if self.received == self.rx_limit and self.sent ==  self.count and not self.poll_timer_started and self.outcome is None:
+                self.poll_timer_started = True
                 self.poll_timer = event.reactor.schedule(0.5, PollTimeout(self))
 
         def run(self):
             Container(self).run()
 
+        def on_accepted(self, event):
+            self.n_accepted += 1
+            if self.received == self.rx_limit and self.n_accepted == self.received and not self.poll_timer_started:
+                self.poll_timer_started = True
+                self.poll_timer = event.reactor.schedule(0.5, PollTimeout(self))
+
+        def on_released(self, event):
+            self.n_released += 1
+            if self.received == self.rx_limit and self.n_released == self.count and not self.poll_timer_started:
+                self.poll_timer_started = True
+                self.poll_timer = event.reactor.schedule(0.5, PollTimeout(self))
+
     def verify_released(self, large_message=False):
         """
         Verify the link released count by releasing all received messages