mirror of https://github.com/python/cpython
gh-117657: Fix race involving immortalizing objects (#119927)
The free-threaded build currently immortalizes objects that use deferred reference counting (see gh-117783). This typically happens once the first non-main thread is created, but the behavior can be suppressed for tests, in subinterpreters, or during a compile() call. This fixes a race condition involving the tracking of whether the behavior is suppressed.
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@ -347,15 +347,11 @@ struct _gc_runtime_state {
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/* gh-117783: Deferred reference counting is not fully implemented yet, so
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as a temporary measure we treat objects using deferred referenence
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counting as immortal. */
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struct {
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/* Immortalize objects instead of marking them as using deferred
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reference counting. */
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int enabled;
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/* Set enabled=1 when the first background thread is created. */
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int enable_on_thread_created;
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} immortalize;
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counting as immortal. The value may be zero, one, or a negative number:
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0: immortalize deferred RC objects once the first thread is created
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1: immortalize all deferred RC objects immediately
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<0: suppressed; don't immortalize objects */
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int immortalize;
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#endif
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};
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@ -529,11 +529,11 @@ def suppress_immortalization(suppress=True):
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yield
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return
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old_values = _testinternalcapi.set_immortalize_deferred(False)
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_testinternalcapi.suppress_immortalization(True)
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try:
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yield
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finally:
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_testinternalcapi.set_immortalize_deferred(*old_values)
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_testinternalcapi.suppress_immortalization(False)
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def skip_if_suppress_immortalization():
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try:
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@ -1966,24 +1966,18 @@ get_py_thread_id(PyObject *self, PyObject *Py_UNUSED(ignored))
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#endif
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static PyObject *
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set_immortalize_deferred(PyObject *self, PyObject *value)
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suppress_immortalization(PyObject *self, PyObject *value)
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{
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#ifdef Py_GIL_DISABLED
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PyInterpreterState *interp = PyInterpreterState_Get();
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int old_enabled = interp->gc.immortalize.enabled;
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int old_enabled_on_thread = interp->gc.immortalize.enable_on_thread_created;
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int enabled_on_thread = 0;
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if (!PyArg_ParseTuple(value, "i|i",
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&interp->gc.immortalize.enabled,
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&enabled_on_thread))
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{
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int suppress = PyObject_IsTrue(value);
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if (suppress < 0) {
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return NULL;
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}
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interp->gc.immortalize.enable_on_thread_created = enabled_on_thread;
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return Py_BuildValue("ii", old_enabled, old_enabled_on_thread);
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#else
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return Py_BuildValue("OO", Py_False, Py_False);
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PyInterpreterState *interp = PyInterpreterState_Get();
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// Subtract two to suppress immortalization (so that 1 -> -1)
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_Py_atomic_add_int(&interp->gc.immortalize, suppress ? -2 : 2);
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#endif
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Py_RETURN_NONE;
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}
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static PyObject *
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@ -1991,7 +1985,7 @@ get_immortalize_deferred(PyObject *self, PyObject *Py_UNUSED(ignored))
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{
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#ifdef Py_GIL_DISABLED
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PyInterpreterState *interp = PyInterpreterState_Get();
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return PyBool_FromLong(interp->gc.immortalize.enable_on_thread_created);
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return PyBool_FromLong(_Py_atomic_load_int(&interp->gc.immortalize) >= 0);
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#else
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Py_RETURN_FALSE;
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#endif
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@ -2111,7 +2105,7 @@ static PyMethodDef module_functions[] = {
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#ifdef Py_GIL_DISABLED
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{"py_thread_id", get_py_thread_id, METH_NOARGS},
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#endif
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{"set_immortalize_deferred", set_immortalize_deferred, METH_VARARGS},
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{"suppress_immortalization", suppress_immortalization, METH_O},
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{"get_immortalize_deferred", get_immortalize_deferred, METH_NOARGS},
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#ifdef _Py_TIER2
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{"uop_symbols_test", _Py_uop_symbols_test, METH_NOARGS},
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@ -110,7 +110,7 @@ should_intern_string(PyObject *o)
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// unless we've disabled immortalizing objects that use deferred reference
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// counting.
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PyInterpreterState *interp = _PyInterpreterState_GET();
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if (interp->gc.immortalize.enable_on_thread_created) {
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if (_Py_atomic_load_int(&interp->gc.immortalize) < 0) {
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return 1;
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}
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#endif
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@ -240,7 +240,7 @@ intern_constants(PyObject *tuple, int *modified)
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PyThreadState *tstate = PyThreadState_GET();
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if (!_Py_IsImmortal(v) && !PyCode_Check(v) &&
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!PyUnicode_CheckExact(v) &&
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tstate->interp->gc.immortalize.enable_on_thread_created)
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_Py_atomic_load_int(&tstate->interp->gc.immortalize) >= 0)
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{
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PyObject *interned = intern_one_constant(v);
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if (interned == NULL) {
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@ -2429,7 +2429,7 @@ _PyObject_SetDeferredRefcount(PyObject *op)
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assert(op->ob_ref_shared == 0);
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_PyObject_SET_GC_BITS(op, _PyGC_BITS_DEFERRED);
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PyInterpreterState *interp = _PyInterpreterState_GET();
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if (interp->gc.immortalize.enabled) {
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if (_Py_atomic_load_int_relaxed(&interp->gc.immortalize) == 1) {
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// gh-117696: immortalize objects instead of using deferred reference
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// counting for now.
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_Py_SetImmortal(op);
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@ -870,15 +870,15 @@ builtin_compile_impl(PyObject *module, PyObject *source, PyObject *filename,
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// gh-118527: Disable immortalization of code constants for explicit
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// compile() calls to get consistent frozen outputs between the default
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// and free-threaded builds.
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// Subtract two to suppress immortalization (so that 1 -> -1)
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PyInterpreterState *interp = _PyInterpreterState_GET();
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int old_value = interp->gc.immortalize.enable_on_thread_created;
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interp->gc.immortalize.enable_on_thread_created = 0;
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_Py_atomic_add_int(&interp->gc.immortalize, -2);
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#endif
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result = Py_CompileStringObject(str, filename, start[compile_mode], &cf, optimize);
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#ifdef Py_GIL_DISABLED
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interp->gc.immortalize.enable_on_thread_created = old_value;
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_Py_atomic_add_int(&interp->gc.immortalize, 2);
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#endif
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Py_XDECREF(source_copy);
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@ -703,11 +703,9 @@ _PyGC_Init(PyInterpreterState *interp)
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{
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GCState *gcstate = &interp->gc;
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if (_Py_IsMainInterpreter(interp)) {
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// gh-117783: immortalize objects that would use deferred refcounting
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// once the first non-main thread is created.
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gcstate->immortalize.enable_on_thread_created = 1;
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}
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// gh-117783: immortalize objects that would use deferred refcounting
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// once the first non-main thread is created (but not in subinterpreters).
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gcstate->immortalize = _Py_IsMainInterpreter(interp) ? 0 : -1;
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gcstate->garbage = PyList_New(0);
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if (gcstate->garbage == NULL) {
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@ -1808,8 +1806,10 @@ _PyGC_ImmortalizeDeferredObjects(PyInterpreterState *interp)
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{
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struct visitor_args args;
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_PyEval_StopTheWorld(interp);
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gc_visit_heaps(interp, &immortalize_visitor, &args);
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interp->gc.immortalize.enabled = 1;
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if (interp->gc.immortalize == 0) {
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gc_visit_heaps(interp, &immortalize_visitor, &args);
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interp->gc.immortalize = 1;
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}
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_PyEval_StartTheWorld(interp);
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}
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@ -1583,9 +1583,7 @@ new_threadstate(PyInterpreterState *interp, int whence)
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}
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else {
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#ifdef Py_GIL_DISABLED
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if (interp->gc.immortalize.enable_on_thread_created &&
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!interp->gc.immortalize.enabled)
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{
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if (_Py_atomic_load_int(&interp->gc.immortalize) == 0) {
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// Immortalize objects marked as using deferred reference counting
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// the first time a non-main thread is created.
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_PyGC_ImmortalizeDeferredObjects(interp);
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@ -47,7 +47,6 @@ race_top:_PyImport_AcquireLock
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race_top:_Py_dict_lookup_threadsafe
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race_top:_imp_release_lock
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race_top:_multiprocessing_SemLock_acquire_impl
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race_top:builtin_compile_impl
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race_top:dictiter_new
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race_top:dictresize
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race_top:insert_to_emptydict
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@ -55,7 +54,6 @@ race_top:insertdict
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race_top:list_get_item_ref
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race_top:make_pending_calls
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race_top:set_add_entry
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race_top:should_intern_string
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race_top:_Py_slot_tp_getattr_hook
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race_top:add_threadstate
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race_top:dump_traceback
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