Give each non-blocking write a distinct task id, refs #2860, #2859

execute_write_fn(fn, block=False) is documented to return "a UUID representing
the queued task". Two things stopped that being true.

_send_to_write_thread() derived the id from uuid.uuid5(NAMESPACE_DNS,
"datasette.io"), which is deterministic, so every non-blocking write in every
database in every process returned 3f143baa-4e3d-5842-a36f-4fa2f683b72f. A
constant cannot identify a particular task. Now uuid4(). Refs #2860.

With num_sql_threads=0 there is no write thread, so execute_write_fn took the
synchronous branch and `result` was the write function's return value, normally
None. The block=False path then unpacked it unconditionally and raised
TypeError: cannot unpack non-iterable NoneType object. The non-threaded branch
now returns the same (task_id, reply_future) shape, with the future already
resolved because the write has finished, so both modes share one code path.
Refs #2859.

test_execute_write_fn_block_false only asserted isinstance(task_id, uuid.UUID),
which a constant satisfies. The new test is parametrized over threaded and
non-threaded and asserts two calls return different ids, so either regression
fails it.

.github/workflows/test.yml

@@ -11,16 +11,17 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.15"]
     steps:
     - uses: actions/checkout@v7
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v6
+      uses: actions/setup-python@v7
       with:
         python-version: ${{ matrix.python-version }}
         allow-prereleases: true
         cache: pip
         cache-dependency-path: pyproject.toml
+        check-latest: true
     - name: Build extension for --load-extension test
       run: |-
         (cd tests && gcc ext.c -fPIC -shared -o ext.so)

datasette/app.py

@@ -453,8 +453,10 @@ class Datasette:
         self.databases = collections.OrderedDict()
         self.actions = {}  # .invoke_startup() will populate this
         self._column_types = {}  # .invoke_startup() will populate this
+        self._setup_db_done = False
         try:
             self._refresh_schemas_lock = asyncio.Lock()
+            self._startup_lock = asyncio.Lock()
         except RuntimeError as rex:
             # Workaround for intermittent test failure, see:
             # https://github.com/simonw/datasette/issues/1802
@@ -462,6 +464,7 @@ class Datasette:
                 loop = asyncio.new_event_loop()
                 asyncio.set_event_loop(loop)
                 self._refresh_schemas_lock = asyncio.Lock()
+                self._startup_lock = asyncio.Lock()
             else:
                 raise
         self.crossdb = crossdb
@@ -2803,24 +2806,52 @@ class Datasette:
             raise RowNotFound(db.name, table_name, pk_values)
         return ResolvedRow(db, table_name, sql, params, pks, pk_values, results.first())
 
+    async def _startup_sequence(self):
+        """Idempotently run the full startup sequence: table counts for
+        immutable databases, then invoke_startup(). Safe to call more than
+        once and safe to call concurrently - callers block until whichever
+        call got there first has finished.
+
+        This is the single entry point used by both AsgiLifespan (so
+        real deployments finish startup before accepting requests) and
+        AsgiRunOnFirstRequest (the fallback for hosts that never send
+        lifespan events, e.g. DatasetteClient's httpx.ASGITransport), and
+        `datasette serve` (cli.py) calls it too. The fast path below checks
+        both `_startup_invoked` and `_setup_db_done` - not just the former -
+        so that a bare `await ds.invoke_startup()` made by a caller ahead of
+        `_startup_sequence()` (which only sets `_startup_invoked`) can't
+        make this method skip the immutable-database table-count precompute.
+        """
+        if self._startup_invoked and self._setup_db_done:
+            return
+        async with self._startup_lock:
+            if self._startup_invoked and self._setup_db_done:
+                return
+            if not self._setup_db_done:
+                # First time server starts up, calculate table counts for
+                # immutable databases
+                for database in self.databases.values():
+                    if not database.is_mutable:
+                        await database.table_counts(limit=60 * 60 * 1000)
+                self._setup_db_done = True
+            await self.invoke_startup()
+
     def app(self):
         """Returns an ASGI app function that serves the whole of Datasette"""
         routes = self._routes()
 
-        async def setup_db():
-            # First time server starts up, calculate table counts for immutable databases
-            for database in self.databases.values():
-                if not database.is_mutable:
-                    await database.table_counts(limit=60 * 60 * 1000)
-
         async def _close_on_shutdown():
             self.close()
 
         asgi = CrossOriginProtectionMiddleware(DatasetteRouter(self, routes), self)
         if self.setting("trace_debug"):
             asgi = AsgiTracer(asgi)
-        asgi = AsgiLifespan(asgi, on_shutdown=[_close_on_shutdown])
+        asgi = AsgiLifespan(
-        asgi = AsgiRunOnFirstRequest(asgi, on_startup=[setup_db, self.invoke_startup])
+            asgi,
+            on_startup=[self._startup_sequence],
+            on_shutdown=[_close_on_shutdown],
+        )
+        asgi = AsgiRunOnFirstRequest(asgi, on_startup=[self._startup_sequence])
         for wrapper in pm.hook.asgi_wrapper(datasette=self):
             asgi = wrapper(asgi)
         return asgi

datasette/cli.py

@@ -670,11 +670,9 @@ def serve(
         raise click.ClickException("--token can only be used with --get")
 
     if get:
-        # Run async soundness checks before startup hooks, since invoke_startup
+        # --get means we don't run Uvicorn at all
-        # now populates internal tables which requires querying each database
         run_sync(lambda: check_databases(ds))
 
-        # Run the "startup" plugin hooks
         try:
             run_sync(ds.invoke_startup)
         except StartupError as e:
@@ -709,13 +707,15 @@ def serve(
     # on the loop (asyncio.create_task, Lock/Queue/Event objects, ...) is
     # still alive when the server starts handling requests.
     async def _serve_async():
-        # Run async soundness checks before startup hooks, since invoke_startup
+        # Populate internal catalog tables before invoke_startup
-        # now populates internal tables which requires querying each database
         await check_databases(ds)
 
-        # Run the "startup" plugin hooks
+        # Run the full startup sequence (immutable-database table-count
+        # precompute + the "startup" plugin hooks) via the same entry point
+        # AsgiLifespan/AsgiRunOnFirstRequest use, so it's not skipped when
+        # uvicorn's lifespan.startup fires moments later.
         try:
-            await ds.invoke_startup()
+            await ds._startup_sequence()
         except StartupError as e:
             raise click.ClickException(e.args[0])
 

datasette/database.py

@@ -354,6 +354,15 @@ class Database:
                     result = fn(self._write_connection)
             else:
                 result = fn(self._write_connection)
+            if not block:
+                # There is no write thread here, so the write has already
+                # finished. Hand back the same (task_id, reply_future) shape
+                # _send_to_write_thread() returns, with the future already
+                # resolved, so the block=False path below is identical in
+                # both modes.
+                reply_future = asyncio.get_running_loop().create_future()
+                reply_future.set_result(result)
+                result = (uuid.uuid4(), reply_future)
         else:
             result = await self._send_to_write_thread(
                 fn, block=block, transaction=transaction
@@ -425,7 +434,7 @@ class Database:
             )
             self._write_thread.name = f"_execute_writes for database {self.name}"
             self._write_thread.start()
-        task_id = uuid.uuid5(uuid.NAMESPACE_DNS, "datasette.io")
+        task_id = uuid.uuid4()
         loop = asyncio.get_running_loop()
         reply_future = loop.create_future()
         self._write_queue.put(

datasette/utils/asgi.py

@@ -1,3 +1,4 @@
+import asyncio
 import json
 import re
 from http.cookies import Morsel, SimpleCookie
@@ -300,12 +301,24 @@ class AsgiLifespan:
             while True:
                 message = await receive()
                 if message["type"] == "lifespan.startup":
-                    for fn in self.on_startup:
+                    try:
-                        await fn()
+                        for fn in self.on_startup:
+                            await fn()
+                    except Exception as e:  # noqa: BLE001
+                        await send(
+                            {"type": "lifespan.startup.failed", "message": str(e)}
+                        )
+                        return
                     await send({"type": "lifespan.startup.complete"})
                 elif message["type"] == "lifespan.shutdown":
-                    for fn in self.on_shutdown:
+                    try:
-                        await fn()
+                        for fn in self.on_shutdown:
+                            await fn()
+                    except Exception as e:  # noqa: BLE001
+                        await send(
+                            {"type": "lifespan.shutdown.failed", "message": str(e)}
+                        )
+                        return
                     await send({"type": "lifespan.shutdown.complete"})
                     return
         else:
@@ -624,10 +637,23 @@ class AsgiRunOnFirstRequest:
         self.asgi = asgi
         self.on_startup = on_startup
         self._started = False
+        # Guards against concurrent early requests interleaving with startup:
+        # without this, several requests could all observe `_started is
+        # False` and proceed before any of them finish running the hooks.
+        self._lock = asyncio.Lock()
 
     async def __call__(self, scope, receive, send):
-        if not self._started:
+        # Leave "lifespan" scope events alone - this shim only exists as a
-            self._started = True
+        # fallback for hosts that never send them. It wraps AsgiLifespan, so
-            for hook in self.on_startup:
+        # if it ran on_startup here too, a startup exception would escape
-                await hook()
+        # before AsgiLifespan's own try/except got a chance to turn it into
+        # a lifespan.startup.failed message.
+        if scope["type"] != "lifespan" and not self._started:
+            async with self._lock:
+                # Re-check: another request may have finished startup while
+                # we were waiting for the lock.
+                if not self._started:
+                    for hook in self.on_startup:
+                        await hook()
+                    self._started = True
         return await self.asgi(scope, receive, send)

tests/test_cli_serve_server.py

@@ -127,11 +127,6 @@ def test_startup_error_fails_fast_before_port_binds(serve_with_plugins):
     A "startup" plugin hook that raises StartupError must fail fast: print
     the message, exit non-zero, and never accept a connection on the port -
     the failure must happen before uvicorn.Server binds the socket.
-
-    Note this is a characterization test, not a regression test: it also
-    passes on unmodified main, where startup already ran ahead of
-    uvicorn.run(). It earns its keep once startup moves into the ASGI
-    lifespan, where fail-fast is genuinely at risk.
     """
     proc, port = serve_with_plugins(
         {"startup_error_plugin": STARTUP_ERROR_PLUGIN}, wait_for_startup=False

tests/test_internals_database.py

@@ -705,6 +705,33 @@ async def test_execute_write_fn_block_false(db):
     assert isinstance(task_id, uuid.UUID)
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("disable_threads", (False, True))
+async def test_execute_write_fn_block_false_returns_uuid(tmp_path, disable_threads):
+    # block=False is documented to return "a UUID representing the queued task".
+    # With num_sql_threads=0 there is no write thread, so the non-threaded branch
+    # has to satisfy the same contract as the threaded one.
+    settings = {"num_sql_threads": 0} if disable_threads else {}
+    ds = Datasette([], memory=True, settings=settings)
+    await ds.invoke_startup()
+    db = ds.add_memory_database("test_block_false")
+    await db.execute_write(
+        "create table if not exists t (id integer primary key, v text)"
+    )
+
+    def write_fn(conn):
+        conn.execute("insert into t (v) values ('a')")
+        # Returns None, like most write functions.
+
+    task_id = await db.execute_write_fn(write_fn, block=False)
+
+    assert isinstance(task_id, uuid.UUID)
+    # Distinct per call, so a caller can tell two queued tasks apart.
+    second = await db.execute_write_fn(write_fn, block=False)
+    assert isinstance(second, uuid.UUID)
+    assert second != task_id
+
+
 @pytest.mark.asyncio
 async def test_execute_write_fn_block_true(db):
     def write_fn(conn):

tests/test_lifespan.py

@@ -0,0 +1,259 @@
+"""
+Tests for wiring Datasette startup (setup_db table counts + invoke_startup)
+into the ASGI lifespan protocol.
+
+These exercise Datasette._startup_sequence() via three different callers:
+- AsgiLifespan, by hand-driving lifespan.startup messages (no HTTP request)
+- AsgiRunOnFirstRequest, the fallback for hosts that never send lifespan
+  events (this is what DatasetteClient / plain httpx.ASGITransport uses)
+- Both at once, to prove startup hooks run at most once
+"""
+
+import asyncio
+import contextlib
+import sqlite3
+
+import httpx
+import pytest
+
+from datasette import hookimpl
+from datasette.app import Datasette
+from datasette.database import Database
+from datasette.plugins import pm
+
+
+async def _drive_lifespan_startup(app):
+    """Send a single lifespan.startup message into app's ASGI lifespan loop
+    and return the list of messages sent back - without ever sending
+    lifespan.shutdown. Mirrors what a real server does: after startup
+    completes it parks waiting for the next event. We cancel that wait
+    once we've observed the startup response, rather than closing the
+    Datasette instance down with a shutdown message.
+    """
+    messages_sent = []
+    startup_responded = asyncio.Event()
+    delivered = False
+
+    async def receive():
+        nonlocal delivered
+        if not delivered:
+            delivered = True
+            return {"type": "lifespan.startup"}
+        # No further messages: block until the task is cancelled below,
+        # same as a real server parked waiting for lifespan.shutdown.
+        await asyncio.Event().wait()
+
+    async def send(message):
+        messages_sent.append(message)
+        startup_responded.set()
+
+    task = asyncio.create_task(app({"type": "lifespan"}, receive, send))
+    try:
+        await asyncio.wait_for(startup_responded.wait(), timeout=5)
+    finally:
+        task.cancel()
+        with contextlib.suppress(asyncio.CancelledError):
+            await task
+    return messages_sent
+
+
+@pytest.mark.asyncio
+async def test_lifespan_startup_runs_before_any_request():
+    ds = Datasette(memory=True)
+    assert ds._startup_invoked is False
+    app = ds.app()
+
+    messages = await _drive_lifespan_startup(app)
+
+    assert {"type": "lifespan.startup.complete"} in messages
+    assert ds._startup_invoked is True
+    # Internal catalog tables should be populated too, entirely without an
+    # HTTP request having been made.
+    internal_db = ds.get_internal_database()
+    databases = await internal_db.execute("select * from catalog_databases")
+    assert len(databases.rows) >= 1
+
+
+@pytest.mark.asyncio
+async def test_lifespan_startup_failure_reports_lifespan_startup_failed():
+    class RaisingStartupPlugin:
+        __name__ = "RaisingStartupPlugin"
+
+        @hookimpl
+        def startup(self, datasette):
+            async def inner():
+                raise RuntimeError("boom from startup hook")
+
+            return inner
+
+    ds = Datasette(memory=True)
+    pm.register(RaisingStartupPlugin(), name="raising_startup_plugin")
+    try:
+        app = ds.app()
+        messages = await _drive_lifespan_startup(app)
+    finally:
+        pm.unregister(name="raising_startup_plugin")
+
+    assert messages == [
+        {"type": "lifespan.startup.failed", "message": "boom from startup hook"}
+    ]
+    # The exception happened before invoke_startup() got to the end of its
+    # body, so startup is not considered to have completed.
+    assert ds._startup_invoked is False
+
+
+@pytest.mark.asyncio
+async def test_startup_runs_exactly_once_across_lifespan_and_first_request():
+    call_count = {"n": 0}
+
+    class CountingStartupPlugin:
+        __name__ = "CountingStartupPlugin"
+
+        @hookimpl
+        def startup(self, datasette):
+            async def inner():
+                call_count["n"] += 1
+
+            return inner
+
+    ds = Datasette(memory=True)
+    pm.register(CountingStartupPlugin(), name="counting_startup_plugin")
+    try:
+        # Build the ASGI app once, the way a real deployment does - and
+        # reuse the SAME app instance for both the lifespan drive and the
+        # HTTP requests below, since a fresh ds.app() call would reset the
+        # AsgiRunOnFirstRequest fallback's state.
+        app = ds.app()
+
+        messages = await _drive_lifespan_startup(app)
+        assert {"type": "lifespan.startup.complete"} in messages
+        assert call_count["n"] == 1
+
+        # A first HTTP request (as if the host never sent lifespan events,
+        # or lifespan already ran) should not run the hook again.
+        transport = httpx.ASGITransport(app=app)
+        async with httpx.AsyncClient(
+            transport=transport, base_url="http://localhost"
+        ) as client:
+            response1 = await client.get("/-/versions.json")
+            assert response1.status_code == 200
+            # ... nor should a second, repeat request.
+            response2 = await client.get("/-/versions.json")
+            assert response2.status_code == 200
+    finally:
+        pm.unregister(name="counting_startup_plugin")
+
+    assert call_count["n"] == 1
+
+
+@pytest.mark.asyncio
+async def test_no_lifespan_first_request_still_triggers_startup():
+    # Pin today's behavior: a client that never drives ASGI lifespan events
+    # at all (like httpx.ASGITransport, which DatasetteClient uses) still
+    # gets startup armed by the AsgiRunOnFirstRequest fallback.
+    ds = Datasette(memory=True)
+    assert ds._startup_invoked is False
+    app = ds.app()
+    transport = httpx.ASGITransport(app=app)
+    async with httpx.AsyncClient(
+        transport=transport, base_url="http://localhost"
+    ) as client:
+        response = await client.get("/-/versions.json")
+        assert response.status_code == 200
+
+    assert ds._startup_invoked is True
+    internal_db = ds.get_internal_database()
+    databases = await internal_db.execute("select * from catalog_databases")
+    assert len(databases.rows) >= 1
+
+
+@pytest.mark.asyncio
+async def test_datasette_client_first_request_triggers_startup():
+    # Same as above, but through the real DatasetteClient (ds.client) that
+    # plugins and tests actually use, to confirm nothing regressed there.
+    ds = Datasette(memory=True)
+    assert ds._startup_invoked is False
+    response = await ds.client.get("/-/versions.json")
+    assert response.status_code == 200
+    assert ds._startup_invoked is True
+
+
+@pytest.mark.asyncio
+async def test_concurrent_first_requests_all_wait_for_slow_startup():
+    call_count = {"n": 0}
+
+    class SlowStartupPlugin:
+        __name__ = "SlowStartupPlugin"
+
+        @hookimpl
+        def startup(self, datasette):
+            async def inner():
+                call_count["n"] += 1
+                await asyncio.sleep(0.2)
+
+            return inner
+
+    ds = Datasette(memory=True)
+    pm.register(SlowStartupPlugin(), name="slow_startup_plugin")
+    try:
+        app = ds.app()
+        transport = httpx.ASGITransport(app=app)
+        async with httpx.AsyncClient(
+            transport=transport, base_url="http://localhost"
+        ) as client:
+            responses = await asyncio.gather(
+                *[client.get("/-/versions.json") for _ in range(10)]
+            )
+    finally:
+        pm.unregister(name="slow_startup_plugin")
+
+    # Every one of the 10 simultaneous first requests must have blocked
+    # until startup actually finished, not raced ahead of it.
+    assert all(response.status_code == 200 for response in responses)
+    assert call_count["n"] == 1
+    assert ds._startup_invoked is True
+
+
+@pytest.mark.asyncio
+async def test_setup_db_still_runs_when_invoke_startup_ran_first(tmp_path, monkeypatch):
+    # Regression test: `datasette serve` (cli.py _serve_async) calls
+    # ds.invoke_startup() directly, before uvicorn ever sends a
+    # lifespan.startup event that drives _startup_sequence(). If
+    # _startup_sequence()'s fast path only checked `_startup_invoked`, it
+    # would see startup already done and skip the immutable-database
+    # table-count precompute (setup_db) entirely - a silent regression
+    # versus main, where AsgiRunOnFirstRequest ran setup_db unconditionally
+    # on request #1.
+    db_path = tmp_path / "immutable.db"
+    conn = sqlite3.connect(str(db_path))
+    conn.execute("create table t (id integer primary key)")
+    conn.commit()
+    conn.close()
+
+    ds = Datasette([], immutables=[str(db_path)])
+
+    call_count = {"n": 0}
+    original_table_counts = Database.table_counts
+
+    async def counting_table_counts(self, *args, **kwargs):
+        call_count["n"] += 1
+        return await original_table_counts(self, *args, **kwargs)
+
+    monkeypatch.setattr(Database, "table_counts", counting_table_counts)
+
+    # Simulate the CLI path: invoke_startup() runs directly and completes
+    # BEFORE _startup_sequence() ever gets a chance to run setup_db.
+    await ds.invoke_startup()
+    assert ds._startup_invoked is True
+    assert call_count["n"] == 0
+
+    # The lifespan/first-request path (or the CLI itself, per the fix)
+    # calling the shared entry point afterwards must still precompute
+    # table counts for immutable databases.
+    await ds._startup_sequence()
+    assert call_count["n"] == 1
+    assert ds._setup_db_done is True
+
+    # Idempotency: a second call must not recompute.
+    await ds._startup_sequence()
+    assert call_count["n"] == 1