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gh-151644: Fix data race in sys.setdlopenflags/getdlopenflags under free-threading #151768

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gh-151644: Fix data race in sys.setdlopenflags/getdlopenflags under free-threading #151768

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99b6011
gh-151644: Fix data race in sys.setdlopenflags/getdlopenflags under f…
zangjiucheng Jun 20, 2026
f75b2c7
Misc/NEWS.d: fix news entry filename format for gh-151644
zangjiucheng Jun 20, 2026
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21 changes: 21 additions & 0 deletions Lib/test/test_free_threading/test_sys.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,27 @@


class SysModuleTest(unittest.TestCase):
@unittest.skipUnless(hasattr(sys, "setdlopenflags"),
"test needs sys.setdlopenflags()")
def test_dlopenflags_concurrent(self):
# gh-151644: getdlopenflags() and setdlopenflags() must be safe to
# call concurrently in free-threaded builds.
original = sys.getdlopenflags()
self.addCleanup(sys.setdlopenflags, original)

# Use a small set of known-valid flag values to avoid integer overflow.
flag_values = [1, 2, 256, 257]

def worker(worker_id):
for i in range(20_000):
if worker_id % 2 == 0:
sys.getdlopenflags()
else:
sys.setdlopenflags(flag_values[worker_id % len(flag_values)])

workers = [lambda i=i: worker(i) for i in range(6)]
threading_helper.run_concurrently(workers)

def test_int_max_str_digits_thread(self):
# gh-151218: Check that it's safe to call get_int_max_str_digits() and
# set_int_max_str_digits() in parallel. Previously, this test triggered
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4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-18-00-00-00.gh-issue-151644.5cFffN.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
Fix a data race in :func:`sys.setdlopenflags` and :func:`sys.getdlopenflags`
when called concurrently in the free-threaded build. The underlying
``_PyImport_GetDLOpenFlags`` and ``_PyImport_SetDLOpenFlags`` functions now
use atomic load/store operations.
4 changes: 2 additions & 2 deletions Python/import.c
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Original file line number Diff line number Diff line change
Expand Up @@ -908,13 +908,13 @@ _PyImport_SwapPackageContext(const char *newcontext)
int
_PyImport_GetDLOpenFlags(PyInterpreterState *interp)
{
return DLOPENFLAGS(interp);
return FT_ATOMIC_LOAD_INT_RELAXED(DLOPENFLAGS(interp));
}

void
_PyImport_SetDLOpenFlags(PyInterpreterState *interp, int new_val)
{
DLOPENFLAGS(interp) = new_val;
FT_ATOMIC_STORE_INT_RELAXED(DLOPENFLAGS(interp), new_val);
}
#endif // HAVE_DLOPEN

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