Fix: SQS fails to get newly-visible messages when long polling (#5733)

The [original commit to remove the `sleep` call][1], only considered newly-arriving
messages; but didn't take into account that existing messages could become visible
in a much shorter time duration than the wait timeout.  This commit addresses this
by checking for newly-visible messages at the visibility timeout granularity (seconds),
which is still a major improvement over the original 10 millisecond polling.

[1]: <d560ff002d> "Remove Sleep Call"

moto/sqs/models.py

@@ -949,7 +949,7 @@ class SQSBackend(BaseBackend):
                     # so break to avoid an infinite loop.
                     break
 
-                queue.wait_for_messages(wait_seconds_timeout)
+                queue.wait_for_messages(1)
                 continue
 
             previous_result_count = len(result)

tests/test_sqs/test_sqs.py

@@ -3180,3 +3180,20 @@ def test_message_delay_is_more_than_15_minutes():
     response["Messages"][0]["Attributes"]["MessageDeduplicationId"].should.equal(
         "message_deduplication_id_1"
     )
+
+
+@mock_sqs
+def test_receive_message_that_becomes_visible_while_long_polling():
+    sqs = boto3.resource("sqs", region_name="us-east-1")
+    queue = sqs.create_queue(QueueName="test-queue")
+    msg_body = str(uuid4())
+    queue.send_message(MessageBody=msg_body)
+    messages = queue.receive_messages()
+    messages[0].change_visibility(VisibilityTimeout=1)
+    time_to_wait = 2
+    begin = time.time()
+    messages = queue.receive_messages(WaitTimeSeconds=time_to_wait)
+    end = time.time()
+    assert len(messages) == 1
+    assert messages[0].body == msg_body
+    assert end - begin < time_to_wait