[New-bugs-announce] [issue33608] Add a cross-interpreter-safe mechanism to indicate that an object may be destroyed.

[Eric Snow]

New submission from Eric Snow <ericsnowcurrently at gmail.com>:

In order to keep subinterpreters properly isolated, objects
from one interpreter should not be used in C-API calls in
another interpreter.  That is relatively straight-forward
except in one case: indicating that the other interpreter
doesn't need the object to exist any more (similar to
PyBuffer_Release() but more general).  I consider the
following solutions to be the most viable.  Both make use
of recounts to protect cross-interpreter usage (with incref
before sharing).

1. manually switch interpreters (new private function)
  a. acquire the GIL
  b. if refcount > 1 then decref and release the GIL
  c. switch
  d. new thread (or re-use dedicated one)
  e. decref
  f. kill thread
  g. switch back
  h. release the GIL
2. change pending call mechanism (see Py_AddPendingCall) to
   per-interpreter instead of global (add "interp" arg to
   signature of new private C-API function)
  a. queue a function that decrefs the object
3. new cross-interpreter-specific private C-API function
  a. queue the object for decref (a la Py_AddPendingCall)
     in owning interpreter

I favor #2, since it is more generally applicable.  #3 would
probably be built on #2 anyway.  #1 is relatively inefficient.
With #2, Py_AddPendingCall() would become a simple wrapper
around the new private function.

----------
messages: 317333
nosy: eric.snow, ncoghlan, serhiy.storchaka, vstinner, yselivanov
priority: normal
severity: normal
stage: needs patch
status: open
title: Add a cross-interpreter-safe mechanism to indicate that an object may be destroyed.
versions: Python 3.4

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33608>
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