From 75e71176cb260e7e6eadbf916b984741fac4fa15 Mon Sep 17 00:00:00 2001 From: "lancedb-gatefixer[bot]" <313497061+lancedb-gatefixer[bot]@users.noreply.github.com> Date: Wed, 23 Sep 2026 14:24:04 -0700 Subject: [PATCH] fix(python): prevent BlobFile finalizer panics on Tokio workers (#4291) ## Cause `io.RawIOBase.__del__` checks `closed` and calls `close()` during GC. Both PyO3 methods entered `block_on`, which panics when GC runs on a LanceDB Tokio worker. ## Fix Track Python blob handle closure atomically so `closed` is synchronous. `close()` marks the handle closed immediately and, when called on a Tokio thread, schedules the underlying async cleanup without blocking that thread. Reads and seeks after close fail immediately; ordinary callers still wait for cleanup. ## Validation - Rebuilt the Python extension with `uv run --extra tests --extra dev maturin develop --extras tests,dev`. - Ran the blob test file and remote blob handle test: 69 passed, 1 skipped. - Ran `cargo fmt --all`, `ruff format .`, and `ruff check .`. Fixes #4283 Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com> --- python/python/tests/test_blob.py | 64 +++++++++++++++++++++++++++ python/python/tests/test_remote_db.py | 4 ++ python/src/runtime.rs | 21 +++++++++ python/src/table.rs | 46 ++++++++++++++++--- 4 files changed, 129 insertions(+), 6 deletions(-) diff --git a/python/python/tests/test_blob.py b/python/python/tests/test_blob.py index 0d3a89c21..cada6e83e 100644 --- a/python/python/tests/test_blob.py +++ b/python/python/tests/test_blob.py @@ -921,6 +921,70 @@ def test_fetch_blob_files_lazy_read(): handles = table.fetch_blob_files("image", [by_id[1]]) assert len(handles) == 1 assert handles[0].read() == payload + handles[0].close() + assert handles[0].closed + with pytest.raises(RuntimeError, match="already closed"): + handles[0].read() + + +def test_blob_file_finalizer_and_close_on_runtime_worker(): + # A tokio panic in IOBase.__del__ is printed but does not fail the add call. + # Run in a child process so the assertion catches that panic on stderr. + script = textwrap.dedent( + """\ + import gc + import threading + + import lancedb + import pyarrow as pa + + db = lancedb.connect("memory:///") + schema = pa.schema([pa.field("id", pa.int64()), lancedb.blob("image")]) + table = db.create_table("finalize", schema=schema) + table.add([{"id": 1, "image": b"first"}]) + hits = table.search().with_row_id(True).limit(1).to_arrow() + row_id = hits["_rowid"][0].as_py() + gc_handle, explicit_handle = table.fetch_blob_files("image", [row_id, row_id]) + + gc.disable() + cycle = [gc_handle] + cycle.append(cycle) + del gc_handle, cycle + + observed = [] + def on_progress(_): + if not observed: + observed.append(( + threading.current_thread() is not threading.main_thread(), + explicit_handle.closed, + gc.collect(), + )) + explicit_handle.close() + + table.add([{"id": 2, "image": b"second"}], progress=on_progress) + gc.enable() + + assert len(observed) == 1, observed + assert observed[0][0] is True, observed + assert observed[0][1] is False, observed + assert observed[0][2] > 0, observed + assert explicit_handle.closed + explicit_handle.close() # Close remains idempotent after the worker call. + try: + explicit_handle.read() + except RuntimeError as error: + assert "already closed" in str(error) + else: + raise AssertionError("a closed blob file was readable") + print("worker close completed") + """ + ) + result = subprocess.run( + [sys.executable, "-c", script], capture_output=True, text=True, check=False + ) + assert result.returncode == 0, result.stderr + assert "Cannot start a runtime from within a runtime" not in result.stderr + assert "worker close completed" in result.stdout def test_fetch_blob_files_null_alignment(): diff --git a/python/python/tests/test_remote_db.py b/python/python/tests/test_remote_db.py index c03862a49..0a357839a 100644 --- a/python/python/tests/test_remote_db.py +++ b/python/python/tests/test_remote_db.py @@ -2470,6 +2470,10 @@ def test_remote_blob_files_are_lazy_seekable_handles(): assert alpha.read_range(1, 3) == b"lph" gamma.seek(2) assert gamma.read() == b"mma" + alpha.close() + assert alpha.closed + with pytest.raises(RuntimeError, match="already closed"): + alpha.read_range(0, 1) def test_remote_blob_fetch_accepts_query_table(): diff --git a/python/src/runtime.rs b/python/src/runtime.rs index 170f7e592..33ffd8bf9 100644 --- a/python/src/runtime.rs +++ b/python/src/runtime.rs @@ -197,6 +197,27 @@ pub fn block_on(fut: F) -> F::Output { get_runtime().block_on(fut) } +/// Run a detached task, including when the caller is already on a runtime worker. +/// Keep it visible to [`shutdown`] until it finishes. +pub fn spawn_background(fut: F) +where + F: Future + Send + 'static, +{ + let guard = OutstandingGuard::new(); + let task = async move { + let _guard = guard; + fut.await; + }; + match runtime::Handle::try_current() { + Ok(handle) => { + let _ = handle.spawn(task); + } + Err(_) => { + let _ = get_runtime().spawn(task); + } + } +} + /// Gracefully quiesce the shared runtime, meant to run at normal process exit. /// /// Waits (bounded by `timeout`) for [`OUTSTANDING`] to reach zero -- i.e. diff --git a/python/src/table.rs b/python/src/table.rs index a3dad3d86..bf5250732 100644 --- a/python/src/table.rs +++ b/python/src/table.rs @@ -1,8 +1,14 @@ // SPDX-License-Identifier: Apache-2.0 // SPDX-FileCopyrightText: Copyright The LanceDB Authors -use std::{collections::HashMap, sync::Arc}; +use std::{ + collections::HashMap, + sync::{ + Arc, + atomic::{AtomicBool, Ordering}, + }, +}; -use crate::runtime::{block_on, future_into_py}; +use crate::runtime::{block_on, future_into_py, spawn_background}; use crate::{ connection::Connection, error::PythonErrorExt, @@ -680,11 +686,23 @@ impl From for DropColumnsResult { #[pyclass(name = "BlobFile")] pub struct PyBlobFile { inner: Arc, + closed: AtomicBool, +} + +impl PyBlobFile { + fn ensure_open(&self) -> PyResult<()> { + if self.closed.load(Ordering::Acquire) { + Err(PyRuntimeError::new_err("blob file is already closed")) + } else { + Ok(()) + } + } } #[pymethods] impl PyBlobFile { fn read_bytes(self_: PyRef<'_, Self>) -> PyResult> { + self_.ensure_open()?; let inner = self_.inner.clone(); let py = self_.py(); let bytes = py @@ -694,6 +712,7 @@ impl PyBlobFile { } pub fn read(self_: PyRef<'_, Self>) -> PyResult> { + self_.ensure_open()?; let inner = self_.inner.clone(); future_into_py(self_.py(), async move { let bytes = inner @@ -705,7 +724,20 @@ impl PyBlobFile { } fn close(self_: PyRef<'_, Self>) -> PyResult<()> { + if self_.closed.swap(true, Ordering::AcqRel) { + return Ok(()); + } let inner = self_.inner.clone(); + if tokio::runtime::Handle::try_current().is_ok() { + // IOBase.__del__ can call close while cyclic GC runs on a worker. + // The status changes immediately; release Lance's async state there. + spawn_background(async move { + if let Err(error) = inner.close().await { + log::warn!("blob close failed: {error}"); + } + }); + return Ok(()); + } self_ .py() .detach(move || block_on(async move { inner.close().await })) @@ -713,13 +745,11 @@ impl PyBlobFile { } fn is_closed(self_: PyRef<'_, Self>) -> bool { - let inner = self_.inner.clone(); - self_ - .py() - .detach(move || block_on(async move { inner.is_closed().await })) + self_.closed.load(Ordering::Acquire) } fn seek(self_: PyRef<'_, Self>, position: u64) -> PyResult<()> { + self_.ensure_open()?; let inner = self_.inner.clone(); self_ .py() @@ -728,6 +758,7 @@ impl PyBlobFile { } fn tell(self_: PyRef<'_, Self>) -> PyResult { + self_.ensure_open()?; let inner = self_.inner.clone(); self_ .py() @@ -741,6 +772,7 @@ impl PyBlobFile { /// Read a blob-local byte range without moving the cursor. fn read_range(self_: PyRef<'_, Self>, offset: u64, length: usize) -> PyResult> { + self_.ensure_open()?; let end = offset .checked_add(length as u64) .ok_or_else(|| PyValueError::new_err("offset + length overflowed"))?; @@ -753,6 +785,7 @@ impl PyBlobFile { } fn read_up_to(self_: PyRef<'_, Self>, length: usize) -> PyResult> { + self_.ensure_open()?; let inner = self_.inner.clone(); let py = self_.py(); let bytes = py @@ -1455,6 +1488,7 @@ impl Table { .map(|handle| { handle.map(|file| PyBlobFile { inner: Arc::new(file), + closed: AtomicBool::new(false), }) }) .collect::>())