Add private _PyThreadState_UncheckedGet() to get the current thread state #70342

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1. vstinner commented on Jan 19, 2016

   

   vstinner

   on Jan 19, 2016

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   The issue bpo-25150 modified pystate.h to hide _PyThreadState_Current. Sadly, this change broke the vmprof project:
   https://mail.python.org/pipermail/python-dev/2016-January/142767.html

   Attached patches adds a new private _PyThreadState_FastGet() function to get the current thread state but don't call Py_FatalError() if it is NULL.

   The patch also uses replace direct access to _PyThreadState_Current with _PyThreadState_FastGet(), except inside ceval.c and pystate.c.

   Calling Py_FatalError() to handle errors is not really a great API... Bad that's a different story, I don't want to break anything here.

   I want to add the private function to Python 3.5.2 because I consider that the removal of the _PyThreadState_Current symbol is a regression introduced in Python 3.5.1.

   We have no rule for the Python private API, it can change *anytime*.
2. njsmith commented on Jan 19, 2016

   

   njsmith

   on Jan 19, 2016

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   Name should be _PyThreadState_UncheckedGet
3. gpshead commented on Jan 19, 2016

   

   gpshead

   on Jan 19, 2016

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   Overall +1 to this private API. I like the UncheckedGet name better than FastGet but don't really care what the name is so long as it keeps this property: It must be non-blocking and safe to call from a signal handler. Returning NULL in the event the value could not be obtained in such a manner is fine (unlikely to happen from the looks of the 3.5 code).

   They are private and this fixes the regression in 3.5.1. people (ab)using these private APIs should be fine writing conditional compilation code to deal with that.

   We've got a similar patch on our CPython 2.7 interpreter at work (more complicated as it must do a non-blocking lock acquire in the old 2.7 code).
4. python-dev commented on Jan 20, 2016

   

   python-devmannequin

   on Jan 20, 2016

   Mannequin

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   New changeset f9461f1e0559 by Victor Stinner in branch '3.5':
   Add _PyThreadState_UncheckedGet()
   https://hg.python.org/cpython/rev/f9461f1e0559

   New changeset d4f13c9a2b07 by Victor Stinner in branch 'default':
   Merge 3.5
   https://hg.python.org/cpython/rev/d4f13c9a2b07
5. vstinner commented on Jan 20, 2016

   

   vstinner

   on Jan 20, 2016

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   Function added

   @fijal: Sorry for the annoyance of the Python 3.5.1 regression.
6. vstinner

   closed this as completedon Jan 20, 2016
7. vstinner

   changed the title [-]Add private _PyThreadState_FastGet() to get the current thread state[/-] [+]Add private _PyThreadState_UncheckedGet() to get the current thread state[/+] on Jan 20, 2016
8. wenzel commented on Apr 25, 2016

   

   wenzelmannequin

   on Apr 25, 2016

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   I've also run into this regression. FWIW this is what I've ended up using to work around it (it's a mess, but what are we to do..)

   #if PY_VERSION_HEX >= 0x03050000 && PY_VERSION_HEX < 0x03050200
   extern "C" {
       /* Manually import _PyThreadState_Current symbol */
       struct _Py_atomic_address { void *value; };
       PyAPI_DATA(_Py_atomic_address) _PyThreadState_Current;
   };
   #endif
   
   PyThreadState *get_thread_state_unchecked() {
   #if   PY_VERSION_HEX < 0x03000000
       return _PyThreadState_Current;
   #elif PY_VERSION_HEX < 0x03050000
       return (PyThreadState*) _Py_atomic_load_relaxed(&_PyThreadState_Current);
   #elif PY_VERSION_HEX < 0x03050200
       return (PyThreadState*) _PyThreadState_Current.value;
   #else
       return _PyThreadState_UncheckedGet();
   #endif
   }
9. ezio-melotti

   transferred this issue fromon Apr 10, 2022