gh-71936: Fix race condition in multiprocessing.Pool#124973
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Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it will call BaseProxy._decref() when it is GCed. This may cause a race condition with Pool(maxtasksperchild=None) on Windows. A connection would be closed and raised TypeError when a GC occurs between _ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in _ConnectionBase.send() in the second or later task, and a new object is allocated that shares the id() of a previously deleted one. Instead of using the id() of the token (or the proxy), use a unique, non-reusable number. Co-Authored-By: Akinori Hattori <hattya@gmail.com>
gpshead
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A couple possible things to improve, but good regardless.
I'm not worried about a regression test for this. Hard, and clearly better than what came before.
gpshead
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Nov 12, 2024
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As I confirmed in #71936 (comment), this solves the problem for me. Will this be back ported? |
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I see no issues in our post-merge testing, so, yes :) |
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Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13. |
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Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12. |
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…124973) * pythongh-71936: Fix race condition in multiprocessing.Pool Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it will call BaseProxy._decref() when it is GCed. This may cause a race condition with Pool(maxtasksperchild=None) on Windows. A connection would be closed and raised TypeError when a GC occurs between _ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in _ConnectionBase.send() in the second or later task, and a new object is allocated that shares the id() of a previously deleted one. Instead of using the id() of the token (or the proxy), use a unique, non-reusable number. (cherry picked from commit ba088c8) Co-authored-by: Petr Viktorin <encukou@gmail.com> Co-Authored-By: Akinori Hattori <hattya@gmail.com>
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GH-126869 is a backport of this pull request to the 3.13 branch. |
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…124973) * pythongh-71936: Fix race condition in multiprocessing.Pool Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it will call BaseProxy._decref() when it is GCed. This may cause a race condition with Pool(maxtasksperchild=None) on Windows. A connection would be closed and raised TypeError when a GC occurs between _ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in _ConnectionBase.send() in the second or later task, and a new object is allocated that shares the id() of a previously deleted one. Instead of using the id() of the token (or the proxy), use a unique, non-reusable number. (cherry picked from commit ba088c8) Co-authored-by: Petr Viktorin <encukou@gmail.com> Co-Authored-By: Akinori Hattori <hattya@gmail.com>
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GH-126870 is a backport of this pull request to the 3.12 branch. |
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… (GH-126870) Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it will call BaseProxy._decref() when it is GCed. This may cause a race condition with Pool(maxtasksperchild=None) on Windows. A connection would be closed and raised TypeError when a GC occurs between _ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in _ConnectionBase.send() in the second or later task, and a new object is allocated that shares the id() of a previously deleted one. Instead of using the id() of the token (or the proxy), use a unique, non-reusable number. (cherry picked from commit ba088c8) Co-authored-by: Petr Viktorin <encukou@gmail.com> Co-authored-by: Akinori Hattori <hattya@gmail.com>
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… (GH-126869) Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it will call BaseProxy._decref() when it is GCed. This may cause a race condition with Pool(maxtasksperchild=None) on Windows. A connection would be closed and raised TypeError when a GC occurs between _ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in _ConnectionBase.send() in the second or later task, and a new object is allocated that shares the id() of a previously deleted one. Instead of using the id() of the token (or the proxy), use a unique, non-reusable number. (cherry picked from commit ba088c8) Co-authored-by: Petr Viktorin <encukou@gmail.com> Co-authored-by: Akinori Hattori <hattya@gmail.com>
picnixz
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…124973) * pythongh-71936: Fix race condition in multiprocessing.Pool Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it will call BaseProxy._decref() when it is GCed. This may cause a race condition with Pool(maxtasksperchild=None) on Windows. A connection would be closed and raised TypeError when a GC occurs between _ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in _ConnectionBase.send() in the second or later task, and a new object is allocated that shares the id() of a previously deleted one. Instead of using the id() of the token (or the proxy), use a unique, non-reusable number. Co-Authored-By: Akinori Hattori <hattya@gmail.com>
ebonnal
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…124973) * pythongh-71936: Fix race condition in multiprocessing.Pool Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it will call BaseProxy._decref() when it is GCed. This may cause a race condition with Pool(maxtasksperchild=None) on Windows. A connection would be closed and raised TypeError when a GC occurs between _ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in _ConnectionBase.send() in the second or later task, and a new object is allocated that shares the id() of a previously deleted one. Instead of using the id() of the token (or the proxy), use a unique, non-reusable number. Co-Authored-By: Akinori Hattori <hattya@gmail.com>
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This is based on @hattya's gh-98274.
As far as I can tell, the race condition is caused by using
id()as a unique identifier, assuming that it can't be reused.@hattya's PR supplements the remote object's id with the id of the proxy. But since
_decrefis called after the proxy is deleted, that id could be reused as well. Note that this is a theoretical concern, I wasn't able to reproduce it.This PR uses a counter (with locked store&increment) to get unique values for
_idset.Unfortunately, I have no idea how to test this :/