Remove microsleep (#1903)

Use `threading.Condition` instead of `sleep()` to prevent high cpu usage while SQS long polling on an empty queue. 

Ref: #871
Ref: #1916

Co-authored-by: Brian Pandola <bpandola@gmail.com>

moto/sqs/models.py

@@ -7,6 +7,7 @@ import string
 import struct
 from copy import deepcopy
 from typing import Dict
+from threading import Condition
 from xml.sax.saxutils import escape
 
 from moto.core.exceptions import RESTError
@@ -257,6 +258,7 @@ class Queue(CloudFormationModel):
         self._messages = []
         self._pending_messages = set()
         self.deleted_messages = set()
+        self._messages_lock = Condition()
 
         now = unix_time()
         self.created_timestamp = now
@@ -536,7 +538,9 @@ class Queue(CloudFormationModel):
                     if diff / 1000 < DEDUPLICATION_TIME_IN_SECONDS:
                         return
 
-        self._messages.append(message)
+        with self._messages_lock:
+            self._messages.append(message)
+            self._messages_lock.notify_all()
 
         for arn, esm in self.lambda_event_source_mappings.items():
             backend = sqs_backends[self.account_id][self.region]
@@ -591,6 +595,10 @@ class Queue(CloudFormationModel):
             new_messages.append(message)
         self._messages = new_messages
 
+    def wait_for_messages(self, timeout):
+        with self._messages_lock:
+            self._messages_lock.wait_for(lambda: self.messages, timeout=timeout)
+
     @classmethod
     def has_cfn_attr(cls, attr):
         return attr in ["Arn", "QueueName"]
@@ -930,13 +938,11 @@ class SQSBackend(BaseBackend):
 
             if previous_result_count == len(result):
                 if wait_seconds_timeout == 0:
-                    # There is timeout and we have added no additional results,
+                    # There is no timeout and no additional results,
                     # so break to avoid an infinite loop.
                     break
 
-                import time
-
-                time.sleep(0.01)
+                queue.wait_for_messages(wait_seconds_timeout)
                 continue
 
             previous_result_count = len(result)

tests/test_sqs/test_server.py

@@ -1,3 +1,4 @@
+import datetime
 import re
 import sure  # noqa # pylint: disable=unused-import
 import threading
@@ -80,3 +81,19 @@ def test_messages_polling():
     # got each message in a separate call to ReceiveMessage, despite the long
     # WaitTimeSeconds
     assert len(messages) == 5
+
+
+def test_no_messages_polling_timeout():
+    backend = server.create_backend_app("sqs")
+    queue_name = "test-queue"
+    test_client = backend.test_client()
+    test_client.put(f"/?Action=CreateQueue&QueueName={queue_name}")
+    wait_seconds = 5
+    start = datetime.datetime.utcnow()
+    test_client.get(
+        f"/123/{queue_name}?Action=ReceiveMessage&MaxNumberOfMessages=1&WaitTimeSeconds={wait_seconds}"
+    )
+    end = datetime.datetime.utcnow()
+    duration = end - start
+    assert duration.seconds >= wait_seconds
+    assert duration.seconds <= wait_seconds + (wait_seconds / 2)