can cause it to get called by multiple threads simultaneously.
Ditto for PyInterpreterState_Delete.
Of the former, the docs say "The interpreter lock need not be held, but may
be held if it is necessary to serialize calls to this function". This
kinda implies it both is and isn't thread-safe.
Of the latter, the docs merely say "The interpreter lock need not be
held.", and the clause about serializing is absent.
I expect it was *believed* these are both thread-safe, and the bit about
serializing via the global lock was meant as a permission rather than a
caution.
I also expect we've never seen a problem here because the Python core
(prior to the _PyPclose fix) only calls these functions once per run.
The Py_NewInterpreter subsystem exposed by the C API (but not used by
Python itself) also calls them, but that subsystem appears to be very
rarely used.
Whatever, they're both thread-safe now.
We occasionally received reports from people getting "invalid tstate"
crashes (this is a fatal error in PyThreadState_Delete()). Finally
several people were able to reproduce it reliably and Tim Peters
discovered that there is a race condition when multiple threads are
calling this function without holding the global interpreter lock (the
function may be called without holding that).
Solved the race condition by adding a lock around the mutating uses of
interp->tstate_head. Tim and Jonathan Giddy have run tests that make
it likely that this fixes the crashes -- although Tim hasn't heard
from the person who reported the original problem.
PyThreadState_GetDict() returns a dictionary that can be used to hold such
state; the caller should pick a unique key and store its state there. If
PyThreadState_GetDict() returns NULL, an exception has been raised (most
likely MemoryError) and the caller should pass on the exception. */
PyObject *
PyThreadState_GetDict()
Tim Peters
Guido van Rossum
Moshe Zadka
Thomas Wouters