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Call Py_Finalize at exit using libc::atexit. #943

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merged 1 commit into from
May 24, 2020
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Call Py_Finalize at exit using libc::atexit. #943

merged 1 commit into from
May 24, 2020

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m-ou-se
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@m-ou-se m-ou-se commented May 23, 2020

This makes sure buffers are flushed, threads are joined, etc. when exiting the process.

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m-ou-se commented May 23, 2020

Maybe this also removes the need for this hack:

pyo3/src/lib.rs

Lines 300 to 305 in 072be6c

e.print($py);
// So when this c api function the last line called printed the error to stderr,
// the output is only written into a buffer which is never flushed because we
// panic before flushing. This is where this hack comes into place
$py.run("import sys; sys.stderr.flush()", None, None)
.unwrap();

@m-ou-se m-ou-se mentioned this pull request May 23, 2020
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davidhewitt
davidhewitt approved these changes May 24, 2020
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Seems like a good idea to me. I wonder if this will also resolve #660

src/gil.rs Show resolved Hide resolved
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Maybe this also removes the need for this hack:

Quite possibly. Does libc::atexit handler also get called on panic?

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m-ou-se commented May 24, 2020 •
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Does libc::atexit handler also get called on panic?

Yes.

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m-ou-se commented May 24, 2020

Does libc::atexit handler also get called on panic?

Yes.

Well, not if the panic is caught and the program keeps running. But it runs if the panic causes the program to exit, yes.

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Great, if you could please add a CHANGELOG and then I'm happy to merge this. I suggest just your commit message minus the implementation detail:

### Changed
- Call `Py_Finalize` at exit. [#943](https://github.com/PyO3/pyo3/pull/943)

But will take any other CHANGELOG message you think is good.

@m-ou-se
Call Py_Finalize at exit using libc::atexit.
febccbf 
This makes sure buffers are flushed, threads are joined, etc. when
exiting the process.
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m-ou-se commented May 24, 2020

Oh right, the changelog. Keep forgetting that file. Updated.

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Great, thanks 😄

I think regarding the hack - you're right that it probably isn't needed any more. But I think order of output still will change. Currently it's flush buffers then panic handler runs, if we remove the hack it'll be panic handler then flush buffers during finalize. So let's leave it there for now, but we might clean up later.

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m-ou-se commented May 24, 2020

Yeah. It's a shame that the CPython API doesn't have a Py_FlushStreams or something.

@davidhewitt davidhewitt merged commit 4355360 into PyO3:master May 24, 2020
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Thank you!

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kngwyu commented May 24, 2020

Thank you!
I think it's OK to remove the import sys; sys.stderr.flush() hack, though we can test that it works.

@davidhewitt davidhewitt mentioned this pull request Jul 9, 2020
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@m-ou-se m-ou-se mentioned this pull request Jul 18, 2020
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