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gh-105699: Use a _Py_hashtable_t for the PyModuleDef Cache (gh-106974)

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This fixes a crasher due to a race condition, triggered infrequently when two isolated (own GIL) subinterpreters simultaneously initialize their sys or builtins modules.  The crash happened due the combination of the "detached" thread state we were using and the "last holder" logic we use for the GIL.  It turns out it's tricky to use the same thread state for different threads.  Who could have guessed?

We solve the problem by eliminating the one object we were still sharing between interpreters.  We replace it with a low-level hashtable, using the "raw" allocator to avoid tying it to the main interpreter.

We also remove the accommodations for "detached" thread states, which were a dubious idea to start with.
This commit is contained in:
Eric Snow 2023-07-28 14:39:08 -06:00 • committed by GitHub
parent 55ed85e49c
commit 8ba4df91ae
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5 changed files with 129 additions and 191 deletions
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69
Python/pystate.c
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@ -1640,75 +1640,6 @@ _PyThreadState_DeleteExcept(PyThreadState *tstate)
}
//-------------------------
// "detached" thread states
//-------------------------
void
_PyThreadState_InitDetached(PyThreadState *tstate, PyInterpreterState *interp)
{
_PyRuntimeState *runtime = interp->runtime;
HEAD_LOCK(runtime);
interp->threads.next_unique_id += 1;
uint64_t id = interp->threads.next_unique_id;
HEAD_UNLOCK(runtime);
init_threadstate(tstate, interp, id);
// We do not call add_threadstate().
}
void
_PyThreadState_ClearDetached(PyThreadState *tstate)
{
assert(!tstate->_status.bound);
assert(!tstate->_status.bound_gilstate);
assert(tstate->datastack_chunk == NULL);
assert(tstate->thread_id == 0);
assert(tstate->native_thread_id == 0);
assert(tstate->next == NULL);
assert(tstate->prev == NULL);
PyThreadState_Clear(tstate);
clear_datastack(tstate);
}
void
_PyThreadState_BindDetached(PyThreadState *tstate)
{
assert(!_Py_IsMainInterpreter(
current_fast_get(tstate->interp->runtime)->interp));
assert(_Py_IsMainInterpreter(tstate->interp));
bind_tstate(tstate);
/* Unlike _PyThreadState_Bind(), we do not modify gilstate TSS. */
}
void
_PyThreadState_UnbindDetached(PyThreadState *tstate)
{
assert(!_Py_IsMainInterpreter(
current_fast_get(tstate->interp->runtime)->interp));
assert(_Py_IsMainInterpreter(tstate->interp));
assert(tstate_is_alive(tstate));
assert(!tstate->_status.active);
assert(gilstate_tss_get(tstate->interp->runtime) != tstate);
unbind_tstate(tstate);
/* This thread state may be bound/unbound repeatedly,
so we must erase evidence that it was ever bound (or unbound). */
tstate->_status.bound = 0;
tstate->_status.unbound = 0;
/* We must fully unlink the thread state from any OS thread,
to allow it to be bound more than once. */
tstate->thread_id = 0;
#ifdef PY_HAVE_THREAD_NATIVE_ID
tstate->native_thread_id = 0;
#endif
}
//----------
// accessors
//----------