https://github.com/python/cpython/commit/d6f77e6a3fa46fa31694d288a3081d5ee76e9d07
commit: d6f77e6a3fa46fa31694d288a3081d5ee76e9d07
branch: main
author: Kumar Aditya <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2026-01-06T12:24:02+05:30
summary:
gh-116738: make entering of `contextvars.Context` thread safe (#143074)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-12-22-16-22-02.gh-issue-116738.caQuq_.rst
M Python/context.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-12-22-16-22-02.gh-issue-116738.caQuq_.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-22-16-22-02.gh-issue-116738.caQuq_.rst
new file mode 100644
index 00000000000000..9fa2039ca81d35
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-22-16-22-02.gh-issue-116738.caQuq_.rst
@@ -0,0 +1 @@
+Fix thread safety of :func:`contextvars.Context.run`.
diff --git a/Python/context.c b/Python/context.c
index 606ce4b1c8f60a..62b582f271ffe5 100644
--- a/Python/context.c
+++ b/Python/context.c
@@ -195,16 +195,20 @@ _PyContext_Enter(PyThreadState *ts, PyObject *octx)
{
ENSURE_Context(octx, -1)
PyContext *ctx = (PyContext *)octx;
+#ifdef Py_GIL_DISABLED
+ int already_entered = _Py_atomic_exchange_int(&ctx->ctx_entered, 1);
+#else
+ int already_entered = ctx->ctx_entered;
+ ctx->ctx_entered = 1;
+#endif
- if (ctx->ctx_entered) {
+ if (already_entered) {
_PyErr_Format(ts, PyExc_RuntimeError,
"cannot enter context: %R is already entered", ctx);
return -1;
}
ctx->ctx_prev = (PyContext *)ts->context; /* borrow */
- ctx->ctx_entered = 1;
-
ts->context = Py_NewRef(ctx);
context_switched(ts);
return 0;
@@ -225,8 +229,9 @@ _PyContext_Exit(PyThreadState *ts, PyObject *octx)
{
ENSURE_Context(octx, -1)
PyContext *ctx = (PyContext *)octx;
+ int already_entered = FT_ATOMIC_LOAD_INT_RELAXED(ctx->ctx_entered);
- if (!ctx->ctx_entered) {
+ if (!already_entered) {
PyErr_Format(PyExc_RuntimeError,
"cannot exit context: %R has not been entered", ctx);
return -1;
@@ -243,7 +248,7 @@ _PyContext_Exit(PyThreadState *ts, PyObject *octx)
Py_SETREF(ts->context, (PyObject *)ctx->ctx_prev);
ctx->ctx_prev = NULL;
- ctx->ctx_entered = 0;
+ FT_ATOMIC_STORE_INT(ctx->ctx_entered, 0);
context_switched(ts);
return 0;
}
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