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W-23459262 fix(python-binding): bound streaming output queue and stop leaking worker threads #122

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Merged
mlischetti merged 1 commit into from
Jul 15, 2026
Merged

W-23459262 fix(python-binding): bound streaming output queue and stop leaking worker threads #122

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32 changes: 24 additions & 8 deletions native-lib/python/src/dataweave/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,10 @@
from threading import Thread
from typing import Any, Callable, Dict, Generator, Iterable, Optional, Union

# Bound for streaming output queues: limits memory under slow/stalled consumers
# by exerting backpressure onto the native producer.
_OUTPUT_QUEUE_MAXSIZE = 512


class DataWeaveError(Exception):
pass
Expand Down Expand Up @@ -567,14 +571,18 @@ def _run_streaming_gen(
inputs_json = json.dumps(normalized_inputs)

_SENTINEL = object()
q: Queue = Queue()
q: Queue = Queue(maxsize=_OUTPUT_QUEUE_MAXSIZE)

@WRITE_CALLBACK
def _write_cb(_ctx, buf, length):
try:
q.put(ctypes.string_at(buf, length))
# With maxsize set, put() blocks when the queue is full, exerting
# backpressure onto the native producer. Timeout prevents indefinite
# blocking if the consumer abandons the generator.
q.put(ctypes.string_at(buf, length), timeout=30)
return 0
except Exception:
# Timeout or other failure: signal the native side to abort.
return -1

def _run_native():
Expand Down Expand Up @@ -606,7 +614,7 @@ def _run_native():
self._lib.graal_detach_thread(worker_thread)
q.put(_SENTINEL)

worker = Thread(target=_run_native, name="dw-streaming-worker", daemon=True)
worker = Thread(target=_run_native, name="dw-streaming-worker", daemon=False)
worker.start()

meta = None
Expand All @@ -619,7 +627,9 @@ def _run_native():
else:
yield item

worker.join()
worker.join(timeout=30)
if worker.is_alive():
raise DataWeaveError("Worker thread timeout after 30 seconds")

if meta is None:
meta = {"success": False, "error": "No metadata received from native call"}
Expand Down Expand Up @@ -708,14 +718,18 @@ def _run_transform_gen(
inputs_json = json.dumps(normalized_inputs)

_SENTINEL = object()
q: Queue = Queue()
q: Queue = Queue(maxsize=_OUTPUT_QUEUE_MAXSIZE)

@WRITE_CALLBACK
def _write_cb(_ctx, buf, length):
try:
q.put(ctypes.string_at(buf, length))
# With maxsize set, put() blocks when the queue is full, exerting
# backpressure onto the native producer. Timeout prevents indefinite
# blocking if the consumer abandons the generator.
q.put(ctypes.string_at(buf, length), timeout=30)
return 0
except Exception:
# Timeout or other failure: signal the native side to abort.
return -1

input_iter = iter(input_stream)
Expand Down Expand Up @@ -764,7 +778,7 @@ def _run_native():
self._lib.graal_detach_thread(worker_thread)
q.put(_SENTINEL)

worker = Thread(target=_run_native, name="dw-transform-worker", daemon=True)
worker = Thread(target=_run_native, name="dw-transform-worker", daemon=False)
worker.start()

meta = None
Expand All @@ -777,7 +791,9 @@ def _run_native():
else:
yield item

worker.join()
worker.join(timeout=30)
if worker.is_alive():
raise DataWeaveError("Worker thread timeout after 30 seconds")

if meta is None:
meta = {"success": False, "error": "No metadata received from native call"}
Expand Down
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