gh-113884: Make queue.SimpleQueue thread-safe in --disable-gil builds by mpage · Pull Request #114161 · python/cpython

mpage · 2024-01-17T00:49:17Z

Make queue.SimpleQueue thread-safe when the GIL is disabled. Queue state is protected by the per-object lock; thread suspension now uses the low-level PyParkingLot abstraction.

Issue: Make queue.SimpleQueue thread-safe in --disable-gil builds #113884

erlend-aasland · 2024-01-17T08:53:48Z

Could you split it up so the ring buffer refactoring is done first, then a follow-up PR to make it thread-safe?

mpage · 2024-01-17T17:27:24Z

Could you split it up so the ring buffer refactoring is done first, then a follow-up PR to make it thread-safe?

@erlend-aasland I think it makes the most sense for these commits to be merged together as part of a single PR. The commits in this PR are structured in a way that they can be reviewed independently. How about we start by reviewing the first commit, which is the ring buffer refactoring, then go from there?

mpage · 2024-01-17T19:31:49Z

Tagging @colesbury

colesbury

Other than the threshold for shrinking and a few minor comments, this looks good to me.

erlend-aasland · 2024-01-18T09:36:43Z

I think it makes the most sense for these commits to be merged together as part of a single PR. The commits in this PR are structured in a way that they can be reviewed independently. How about we start by reviewing the first commit, which is the ring buffer refactoring, then go from there?

AFAICS, the ring buffer refactoring makes for a nice stand-alone PR. It will result in a cleaner Git history, and it will make bisecting easier when hunting for bugs.

mpage · 2024-01-18T18:19:21Z

AFAICS, the ring buffer refactoring makes for a nice stand-alone PR.

I disagree but will split the PR in the interest of moving things forward.

Do you have any suggestions for the appropriate "size" of a PR? This will help me avoid having to split PRs in the future. I've been operating under the assumption that a PR should roughly correspond to a single, self-contained "feature" that stands on its own. I don't think the refactoring fits this model, as it wouldn't make sense to do without the other changes in the PR.

mpage · 2024-01-18T21:00:13Z

Split the ring buffer refactoring out into #114259. Putting this in draft until that PR is merged.

erlend-aasland · 2024-01-19T00:07:43Z

Do you have any suggestions for the appropriate "size" of a PR? This will help me avoid having to split PRs in the future. I've been operating under the assumption that a PR should roughly correspond to a single, self-contained "feature" that stands on its own. I don't think the refactoring fits this model, as it wouldn't make sense to do without the other changes in the PR.

We normally do not mix refactorings and features. Most refactorings are done in order to make the code more readable, and/or structure the code in a more maintainable way. Those are qualities that stand on their own, and can justify a single (or multiple) PRs.

erlend-aasland · 2024-01-19T00:12:42Z

As for PR size, I think it is good to try and keep the diff as small as possible (we don't like churn), and keep the number of changed lines within a couple of hundred lines. (Of course, generated files do not count.)

Methods on SimpleQueue are protected with the per-object lock.

…e-113884.CvEjUE.rst

We're not using `PyThread_acquire_lock_timed`.

…iting

mpage · 2024-01-19T22:58:11Z

I've rebased this against main after the ring buffer refactoring was merged. @colesbury and @erlend-aasland would you please have another look?

colesbury

@mpage - you probably want to mark the PR as "Ready for review" (i.e., not a "Draft")

This LGTM other than one minor comment.

erlend-aasland

Thanks. The parking lot API still feels little bit uncomfortable for me, but AFAICS, this looks good. Perhaps a comment explaining how the hand-off data structure relates to the parking lot API could be beneficial for future readers of the code. I also find the maybe_unparked_thread oddly named. OTOH, I don't have a better suggestion :)

erlend-aasland · 2024-01-23T10:02:00Z

@mpage, I applied my minor suggestions. Let me know what you think of #114161 (comment).

Rename parking lot callback to better reflect what it does. More precise type for whether handoff occurred.

mpage · 2024-01-23T18:27:53Z

@erlend-aasland - I think I've addressed all the comments now, can you take another look?

erlend-aasland

Thank you so much, this is very nice!

…isabled (python#114161) * use the ParkingLot API to manage waiting threads * use Argument Clinic's critical section directive to protect queue methods * remove unnecessary overflow check Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>

kumaraditya303 · 2024-07-25T12:30:16Z

@@ -164,7 +167,7 @@ RingBuf_Put(RingBuf *buf, PyObject *item)
 return -1;


You need to decref item here isn't it?

Yes, I think so

…isabled (python#114161) * use the ParkingLot API to manage waiting threads * use Argument Clinic's critical section directive to protect queue methods * remove unnecessary overflow check Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>

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Make queue.SimpleQueue thread-safe in --disable-gil builds #113884
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mpageand others added 6 commits January 19, 2024 14:12

Use ParkingLot to manage waiting threads
bc7a640

Make SimpleQueue thread-safe with the GIL disabled
65c0b90
Methods on SimpleQueue are protected with the per-object lock.

📜🤖 Added by blurb_it.
d999dd6

Update Misc/NEWS.d/next/Core and Builtins/2024-01-17-00-52-57.gh-issu…
511f59f
…e-113884.CvEjUE.rst

Remove unnecessary overflow check
ad5217a
We're not using `PyThread_acquire_lock_timed`.

Use a clearer name for field indicating whether or not threads are wa…
d3b5547
…iting

mpage force-pushed the gh-113884-ft-simplequeue branch from cdf0917 to d3b5547Compare January 19, 2024 22:30

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erlend-aaslandand others added 2 commits January 23, 2024 12:05

Fix suggestion
60fd0ec

Address review comments
80200f8
Rename parking lot callback to better reflect what it does. More precise type for whether handoff occurred.

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		@@ -164,7 +167,7 @@ RingBuf_Put(RingBuf buf, PyObject item)
		return -1;

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mpage commented Jan 17, 2024•
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