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gh-118727: Don't drop the GIL in drop_gil() unless the current thread holds it (#118745)

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`drop_gil()` assumes that its caller is attached, which means that the current
thread holds the GIL if and only if the GIL is enabled, and the enabled-state
of the GIL won't change. This isn't true, though, because `detach_thread()`
calls `_PyEval_ReleaseLock()` after detaching and
`_PyThreadState_DeleteCurrent()` calls it after removing the current thread
from consideration for stop-the-world requests (effectively detaching it).

Fix this by remembering whether or not a thread acquired the GIL when it last
attached, in `PyThreadState._status.holds_gil`, and check this in `drop_gil()`
instead of `gil->enabled`.

This fixes a crash in `test_multiprocessing_pool_circular_import()`, so I've
reenabled it.
This commit is contained in:
Brett Simmers 2024-05-23 16:59:35 -04:00 • committed by GitHub
parent b30d30c747
commit be1dfccdf2
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5 changed files with 73 additions and 60 deletions
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11
Python/pystate.c
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@ -1843,7 +1843,7 @@ _PyThreadState_DeleteCurrent(PyThreadState *tstate)
#endif
current_fast_clear(tstate->interp->runtime);
tstate_delete_common(tstate);
_PyEval_ReleaseLock(tstate->interp, NULL);
_PyEval_ReleaseLock(tstate->interp, tstate, 1);
free_threadstate((_PyThreadStateImpl *)tstate);
}
@ -2068,7 +2068,7 @@ _PyThreadState_Attach(PyThreadState *tstate)
while (1) {
int acquired_gil = _PyEval_AcquireLock(tstate);
_PyEval_AcquireLock(tstate);
// XXX assert(tstate_is_alive(tstate));
current_fast_set(&_PyRuntime, tstate);
@ -2079,20 +2079,17 @@ _PyThreadState_Attach(PyThreadState *tstate)
}
#ifdef Py_GIL_DISABLED
if (_PyEval_IsGILEnabled(tstate) != acquired_gil) {
if (_PyEval_IsGILEnabled(tstate) && !tstate->_status.holds_gil) {
// The GIL was enabled between our call to _PyEval_AcquireLock()
// and when we attached (the GIL can't go from enabled to disabled
// here because only a thread holding the GIL can disable
// it). Detach and try again.
assert(!acquired_gil);
tstate_set_detached(tstate, _Py_THREAD_DETACHED);
tstate_deactivate(tstate);
current_fast_clear(&_PyRuntime);
continue;
}
_Py_qsbr_attach(((_PyThreadStateImpl *)tstate)->qsbr);
#else
(void)acquired_gil;
#endif
break;
}
@ -2123,7 +2120,7 @@ detach_thread(PyThreadState *tstate, int detached_state)
tstate_deactivate(tstate);
tstate_set_detached(tstate, detached_state);
current_fast_clear(&_PyRuntime);
_PyEval_ReleaseLock(tstate->interp, tstate);
_PyEval_ReleaseLock(tstate->interp, tstate, 0);
}
void