From be797d31fc5461d86d091532107acff33a1dd953 Mon Sep 17 00:00:00 2001
From: "Michael J. Sullivan" <sully@msully.net>
Date: Tue, 12 Mar 2024 18:10:02 -0700
Subject: [PATCH] Add a test for debounce

---
 edb/common/asyncutil.py        |   9 +--
 pyproject.toml                 |   3 +
 tests/common/test_asyncutil.py | 121 +++++++++++++++++++++++++++++++++
 3 files changed, 129 insertions(+), 4 deletions(-)
 create mode 100644 tests/common/test_asyncutil.py

diff --git a/edb/common/asyncutil.py b/edb/common/asyncutil.py
index ae50deb5f06..79fc104973e 100644
--- a/edb/common/asyncutil.py
+++ b/edb/common/asyncutil.py
@@ -21,7 +21,6 @@
 from typing import Callable, TypeVar, Awaitable
 
 import asyncio
-import time
 
 
 _T = TypeVar('_T')
@@ -94,7 +93,7 @@ async def debounce(
     loop = asyncio.get_running_loop()
 
     batch = []
-    last_signal = 0.0
+    last_signal = -MAX_WAIT
     target_time = None
 
     while True:
@@ -120,9 +119,11 @@ async def debounce(
             # not longer than MAX_WAIT.
             elif (
                 target_time is not None
-                and target_time < last_signal + MAX_WAIT
             ):
-                target_time = max(t + DELAY_AMT, target_time)
+                target_time = min(
+                    max(t + DELAY_AMT, target_time),
+                    last_signal + MAX_WAIT,
+                )
 
         # Skip sending the event if we need to wait longer.
         if (
diff --git a/pyproject.toml b/pyproject.toml
index e00c4988278..786d2a3d909 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -37,6 +37,9 @@ test = [
     'ruff~=0.1.6',
     'asyncpg~=0.29.0',
 
+    # Needed for testing asyncutil
+    'async_solipsism==0.5.0',
+
     # Needed for test_docs_sphinx_ext
     'requests-xml~=0.2.3',
 
diff --git a/tests/common/test_asyncutil.py b/tests/common/test_asyncutil.py
new file mode 100644
index 00000000000..b3f24c8774d
--- /dev/null
+++ b/tests/common/test_asyncutil.py
@@ -0,0 +1,121 @@
+#
+# This source file is part of the EdgeDB open source project.
+#
+# Copyright 2016-present MagicStack Inc. and the EdgeDB authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+
+import asyncio
+import unittest
+
+from edb.common import asyncutil
+
+try:
+    import async_solipsism
+except ImportError:
+    async_solipsism = None  # type: ignore
+
+
+def with_fake_event_loop(f):
+    # async_solpsism creates an event loop with, among other things,
+    # a totally fake clock.
+    def new(*args, **kwargs):
+        loop = async_solipsism.EventLoop()
+        try:
+            loop.run_until_complete(f(*args, **kwargs))
+        finally:
+            loop.close()
+
+    return new
+
+
+@unittest.skipIf(async_solipsism is None, 'async_solipsism is missing')
+class TestDebounce(unittest.TestCase):
+
+    @with_fake_event_loop
+    async def test_debounce_01(self):
+        loop = asyncio.get_running_loop()
+        outs = []
+        ins = asyncio.Queue()
+
+        async def output(vs):
+            assert loop.time() == int(loop.time())
+            outs.append((int(loop.time()), vs))
+
+        async def sleep_until(t):
+            await asyncio.sleep(t - loop.time())
+
+        task = asyncio.create_task(asyncutil.debounce(
+            ins.get,
+            output,
+            # Use integers for delays to avoid any possibility of
+            # floating point nonsense
+            max_wait=500,
+            delay_amt=200,
+            max_batch_size=4,
+        ))
+
+        ins.put_nowait(1)
+        await sleep_until(10)
+        ins.put_nowait(2)
+        ins.put_nowait(3)
+        await sleep_until(300)
+        ins.put_nowait(4)
+        ins.put_nowait(5)
+        ins.put_nowait(6)
+        await sleep_until(1000)
+
+        # Time 1000 now
+        ins.put_nowait(7)
+        await sleep_until(1150)
+        ins.put_nowait(8)
+        ins.put_nowait(9)
+        ins.put_nowait(10)
+        await sleep_until(1250)
+        ins.put_nowait(11)
+
+        ins.put_nowait(12)
+        await asyncio.sleep(190)
+        ins.put_nowait(13)
+        await asyncio.sleep(190)
+        ins.put_nowait(14)
+        await asyncio.sleep(190)
+        self.assertEqual(loop.time(), 1820)
+        ins.put_nowait(15)
+
+        # Make sure everything clears out and stop it
+        await asyncio.sleep(10000)
+        task.cancel()
+
+        self.assertEqual(
+            outs,
+            [
+                # First one right away
+                (0, [1]),
+                # Next two added at 10 + 200 tick
+                (210, [2, 3]),
+                # Next three added at 300 + 200 tick
+                (500, [4, 5, 6]),
+                # First at 1000
+                (1000, [7]),
+                # Next group at 1250 when the batch fills up
+                (1250, [8, 9, 10, 11]),
+                # And more at 1750 when time expires on that batch
+                (1750, [12, 13, 14]),
+                # And the next one (queued at 1820) at 200 after it was queued,
+                # since there had been a recent signal when it was queued.
+                (2020, [15]),
+            ],
+        )