Missing Sync bound on PyCFunction::new_closure closures
| Details |
|
| Package |
pyo3 |
| Version |
0.28.3 |
| URL |
PyO3/pyo3#6096 |
| Date |
2026-06-11 |
| Patched versions |
>=0.29.0 |
PyCFunction::new_closure (and the temporary new_closure_bound complement in
the 0.21–0.22 series) required the supplied closure to be Send + 'static but
not Sync. The resulting PyCFunction is a Python callable that can be
invoked from any Python thread, which means the closure may be called
concurrently from multiple threads, and needs a Sync bound to prevent
possible data races.
The problem exists under all Python versions but is particularly vulnerable under
the newer free-threaded Python variant, which do not have serial execution
imposed by the Global Interpreter Lock. Under releases protected by the GIL,
the ability to "detach" from the Python interpreter temporarily inside the closure
(e.g. by Python::detach) makes it possible for interleaved and/or concurrent
execution of various portions of the closure.
PyO3 0.29.0 added a Sync bound to close this thread-safety bug.
See advisory page for additional details.
pyo30.28.3>=0.29.0PyCFunction::new_closure(and the temporarynew_closure_boundcomplement inthe 0.21–0.22 series) required the supplied closure to be
Send + 'staticbutnot
Sync. The resultingPyCFunctionis a Python callable that can beinvoked from any Python thread, which means the closure may be called
concurrently from multiple threads, and needs a
Syncbound to preventpossible data races.
The problem exists under all Python versions but is particularly vulnerable under
the newer free-threaded Python variant, which do not have serial execution
imposed by the Global Interpreter Lock. Under releases protected by the GIL,
the ability to "detach" from the Python interpreter temporarily inside the closure
(e.g. by
Python::detach) makes it possible for interleaved and/or concurrentexecution of various portions of the closure.
PyO3 0.29.0 added a
Syncbound to close this thread-safety bug.See advisory page for additional details.