Replace Janus queue with asyncio.Future

Closes #1752

AI generated patch explanation: https://gisthost.github.io/?e2b8d9c7666e988b5c003ff5e5ef3098

tests/test_internals_database.py

@@ -2,9 +2,12 @@
 Tests for the datasette.database.Database class
 """
 
+import asyncio
+from types import SimpleNamespace
 from datasette.app import Datasette
 from datasette.database import Database, Results, MultipleValues
 from datasette.database import DatasetteClosedError
+from datasette.database import _deliver_write_result
 from datasette.utils.sqlite import sqlite3, sqlite_version
 from datasette.utils import Column
 import pytest
@@ -590,6 +593,37 @@ async def test_execute_write_fn_connection_exception(tmpdir, app_client):
     app_client.ds.remove_database("immutable-db")
 
 
+@pytest.mark.asyncio
+async def test_deliver_write_result_leaves_done_future_alone():
+    loop = asyncio.get_running_loop()
+    reply_future = loop.create_future()
+    reply_future.set_result("original")
+    task = SimpleNamespace(loop=loop, reply_future=reply_future)
+
+    # The write thread can finish after the caller has stopped waiting for the
+    # result. Delivery should notice that the future is already resolved and
+    # leave the caller's outcome alone instead of raising InvalidStateError.
+    _deliver_write_result(task, "replacement", None)
+    await asyncio.sleep(0)
+
+    assert reply_future.result() == "original"
+
+
+@pytest.mark.asyncio
+async def test_deliver_write_result_ignores_closed_loop():
+    closed_loop = asyncio.new_event_loop()
+    closed_loop.close()
+    reply_future = asyncio.get_running_loop().create_future()
+    task = SimpleNamespace(loop=closed_loop, reply_future=reply_future)
+
+    # If the event loop that submitted the write has gone away, the write
+    # thread should drop the result rather than crash while reporting back to
+    # that closed loop.
+    _deliver_write_result(task, "result", None)
+
+    assert not reply_future.done()
+
+
 def table_exists(conn, name):
     return bool(
         conn.execute(

tests/test_write_wrapper.py

@@ -2,6 +2,7 @@
 Tests for the write_wrapper plugin hook.
 """
 
+import asyncio
 from dataclasses import dataclass
 from datasette.app import Datasette
 from datasette.events import Event
@@ -633,8 +634,6 @@ async def test_track_event_with_block_false(ds_with_event_tracking):
     assert task_id is not None
 
     # Give the background task time to complete
-    import asyncio
-
     for _ in range(50):
         if ds._tracked_events:
             break
@@ -644,6 +643,30 @@ async def test_track_event_with_block_false(ds_with_event_tracking):
     assert ds._tracked_events[0].message == "non-blocking"
 
 
+@pytest.mark.asyncio
+async def test_track_event_with_block_false_discarded_on_exception(
+    ds_with_event_tracking,
+):
+    """Events queued by a non-blocking write are discarded if the write fails."""
+    ds = ds_with_event_tracking
+    db = ds.get_database("test")
+
+    def my_write(conn, track_event):
+        track_event(DummyEvent(actor=None, message="should not fire"))
+        raise ValueError("deliberate error")
+
+    task_id = await db.execute_write_fn(my_write, block=False)
+    assert task_id is not None
+
+    # A following blocking write proves the failed non-blocking task has
+    # completed; one more loop turn lets its event-dispatch task observe the
+    # exception and exit.
+    await db.execute_write_fn(lambda conn: conn.execute("select 1"))
+    await asyncio.sleep(0)
+
+    assert ds._tracked_events == []
+
+
 # --- Tests for RenameTableEvent detection ---