[MRG] Improve DUL performance

.gitignore

@@ -93,3 +93,6 @@ ENV/
 
 # Rope project settings
 .ropeproject
+
+# PyCharm
+.idea

pynetdicom/dul.py

@@ -378,14 +378,23 @@ def run_reactor(self) -> None:
         # Main DUL loop
         self._idle_timer.start()
         self.socket = cast("AssociationSocket", self.socket)
+        sleep = False
 
         while True:
             # Let the assoc reactor off the leash
             if not self.assoc._dul_ready.is_set():
                 self.assoc._dul_ready.set()
+                # When single-stepping the reactor, sleep between events so that
+                # test code has time to run.
+                sleep = True
 
-            # This effectively controls how quickly the DUL does anything
-            time.sleep(self._run_loop_delay)
+            if sleep:
+                # If there were no events to process on the previous loop,
+                # sleep before checking again.  Otherwise check immediately.
+
+                # Setting _run_loop_delay higher will use less CPU when idle, but will also
+                # increases the latency to respond to new requests.
+                time.sleep(self._run_loop_delay)
 
             if self._kill_thread:
                 break
@@ -426,9 +435,11 @@ def run_reactor(self) -> None:
                 event = self.event_queue.get(block=False)
             # If the queue is empty, return to the start of the loop
             except queue.Empty:
+                sleep = True
                 continue
 
             self.state_machine.do_action(event)
+            sleep = False
 
     def send_pdu(self, primitive: _PDUPrimitiveType) -> None:
         """Place a primitive in the provider queue to be sent to the peer.

pynetdicom/events.py

@@ -84,6 +84,10 @@ class NotificationEvent(NamedTuple):
     is_intervention: bool = False
     is_notification: bool = True
 
+    def __str__(self) -> str:
+        """String representation of the class."""
+        return self.name
+
 
 # pylint: disable=line-too-long
 EVT_ABORTED = NotificationEvent("EVT_ABORTED", "Association aborted")
@@ -135,6 +139,10 @@ class InterventionEvent(NamedTuple):
     is_intervention: bool = True
     is_notification: bool = False
 
+    def __str__(self) -> str:
+        """String representation of the class."""
+        return self.name
+
 
 EVT_ASYNC_OPS = InterventionEvent("EVT_ASYNC_OPS", "Asynchronous operations negotiation requested")  # noqa
 EVT_SOP_COMMON = InterventionEvent("EVT_SOP_COMMON", "SOP class common extended negotiation requested")  # noqa
@@ -421,6 +429,11 @@ def __init__(
                 )
             setattr(self, kk, vv)
 
+    def __str__(self) -> str:
+        """String representation of the class."""
+        return 'Event(event={}, message_id={}, timestamp={}, is_cancelled={})'\
+            .format(self.event, self.message_id, self.timestamp, self.is_cancelled)
+
     @property
     def action_information(self) -> Dataset:
         """Return an N-ACTION request's `Action Information` as a *pydicom*