bpo-20526: Fix PyThreadState_Clear(): don't decref frame (GH-19120) (GH-19136)
PyThreadState.frame is a borrowed reference, not a strong reference:
PyThreadState_Clear() must not call Py_CLEAR(tstate->frame).
Remove test_threading.test_warnings_at_exit(): we cannot warranty
that the Python thread state of daemon threads is cleared in a
reliable way during Python shutdown.
(cherry picked from commit 5804f878e779712e803be927ca8a6df389d82cdf)
diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index 94b0809..e22b053 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -55,6 +55,7 @@
struct _ts *next;
PyInterpreterState *interp;
+ /* Borrowed reference to the current frame (it can be NULL) */
struct _frame *frame;
int recursion_depth;
char overflowed; /* The stack has overflowed. Allow 50 more calls
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-03-23-18-08-34.bpo-20526.NHNZIv.rst b/Misc/NEWS.d/next/Core and Builtins/2020-03-23-18-08-34.bpo-20526.NHNZIv.rst
new file mode 100644
index 0000000..c808b76
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-03-23-18-08-34.bpo-20526.NHNZIv.rst
@@ -0,0 +1,3 @@
+Fix :c:func:`PyThreadState_Clear()`. ``PyThreadState.frame`` is a borrowed
+reference, not a strong reference: ``PyThreadState_Clear()`` must not call
+``Py_CLEAR(tstate->frame)``.
diff --git a/Python/pystate.c b/Python/pystate.c
index 9f99060..3e10855 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -762,11 +762,19 @@
{
int verbose = tstate->interp->config.verbose;
- if (verbose && tstate->frame != NULL)
+ if (verbose && tstate->frame != NULL) {
+ /* bpo-20526: After the main thread calls
+ _PyRuntimeState_SetFinalizing() in Py_FinalizeEx(), threads must
+ exit when trying to take the GIL. If a thread exit in the middle of
+ _PyEval_EvalFrameDefault(), tstate->frame is not reset to its
+ previous value. It is more likely with daemon threads, but it can
+ happen with regular threads if threading._shutdown() fails
+ (ex: interrupted by CTRL+C). */
fprintf(stderr,
"PyThreadState_Clear: warning: thread still has a frame\n");
+ }
- Py_CLEAR(tstate->frame);
+ /* Don't clear tstate->frame: it is a borrowed reference */
Py_CLEAR(tstate->dict);
Py_CLEAR(tstate->async_exc);