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gh-148891: prevent crash in HAMT #148928

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gh-148891: prevent crash in HAMT #148928

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5493663
fix: prevent crash in hamt
KowalskiThomas Apr 23, 2026
1971be8
misc: add news entry
KowalskiThomas Apr 27, 2026
68e43d0
review: update release note
KowalskiThomas Oct 21, 2026
d6ac3bf
chore: shorten comment
KowalskiThomas Oct 21, 2026
20725f4
chore: shorten comment further
KowalskiThomas Oct 21, 2026
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-04-23-08-36-47.gh-issue-148891.AMMHow.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix a crash in :func:`contextvars.Context.run` where a GC invocation could free the current HAMT during traverse.
11 changes: 10 additions & 1 deletion Python/context.c
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Original file line number Diff line number Diff line change
Expand Up @@ -866,8 +866,13 @@ contextvar_set(PyContextVar *var, PyObject *val)
return -1;
}

// gh-148891: Make a strong reference so a GC during _PyHamt_Assoc will
// not free the HAMT during traversal.
PyHamtObject *old_vars = context_get_current_vars(ctx);
Py_INCREF(old_vars);
PyHamtObject *new_vars = _PyHamt_Assoc(
context_get_current_vars(ctx), (PyObject *)var, val);
old_vars, (PyObject *)var, val);
Py_DECREF(old_vars);
if (new_vars == NULL) {
return -1;
}
Expand All @@ -894,8 +899,12 @@ contextvar_del(PyContextVar *var)
return -1;
}

// gh-148891: Make a strong reference so a GC during _PyHamt_Without will
// not free the HAMT during traversal.
PyHamtObject *vars = context_get_current_vars(ctx);
Py_INCREF(vars);
PyHamtObject *new_vars = _PyHamt_Without(vars, (PyObject *)var);
Py_DECREF(vars);
if (new_vars == NULL) {
return -1;
}
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