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Experiment: Guard add_limit counter using lock #1277

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Experiment: Guard add_limit counter using lock #1277

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7 changes: 5 additions & 2 deletions dlt/extract/resource.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
Any,
Optional,
)
from threading import Lock

from dlt.common.configuration.resolve import inject_section
from dlt.common.configuration.specs import known_sections
Expand Down Expand Up @@ -332,7 +333,7 @@ def add_limit(self, max_items: int) -> "DltResource": # noqa: A003
# make sure max_items is a number, to allow "None" as value for unlimited
if max_items is None:
max_items = -1

counter_lock = Lock()
def _gen_wrap(gen: TPipeStep) -> TPipeStep:
"""Wrap a generator to take the first `max_items` records"""

Expand All @@ -354,7 +355,9 @@ def _gen_wrap(gen: TPipeStep) -> TPipeStep:
for i in gen: # type: ignore # TODO: help me fix this later
yield i
if i is not None:
count += 1
with counter_lock:
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@sultaniman I think all this code is run on the main pipeline thread anyway, so the lock will not help here, but I'm not 100% sure

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Tbh I also didn't dig deeper, my theory was that we submit the work to ThreadPoolExecutor which can potentially case data races.

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operations on integers in CPython are atomic so we are not locking anything. IMO race condition goes deep here and we are better off by making our tests to accept 10th element 🤷

count += 1

# async gen yields awaitable so we must count one awaitable more
# so the previous one is evaluated and yielded.
# new awaitable will be cancelled
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