[3.13] gh-121474: Add threading.Barrier parties arg sanity check. (GH-121480) (GH-122444)

(cherry picked from commit d27a53fc02a87e76066fc4e15ff1fff3922a482d)

Co-authored-by: Clinton <pygeek@users.noreply.github.com>

3 files changed, 8 insertions, 0 deletions

diff --git a/Lib/test/lock_tests.py b/Lib/test/lock_tests.py
index 024c6de..8c8f890 100644
--- a/Lib/test/lock_tests.py
+++ b/Lib/test/lock_tests.py
@@ -1013,6 +1013,10 @@ class BarrierTests(BaseTestCase):
         self.assertEqual(self.barrier.n_waiting, 0)
         self.assertFalse(self.barrier.broken)
 
+    def test_constructor(self):
+        self.assertRaises(ValueError, self.barriertype, parties=0)
+        self.assertRaises(ValueError, self.barriertype, parties=-1)
+
     def test_barrier(self, passes=1):
         """
         Test that a barrier is passed in lockstep
diff --git a/Lib/threading.py b/Lib/threading.py
index 2dcdd0c..94ea2f0 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -689,6 +689,8 @@ class Barrier:
         default for all subsequent 'wait()' calls.
 
         """
+        if parties < 1:
+            raise ValueError("parties must be > 0")
         self._cond = Condition(Lock())
         self._action = action
         self._timeout = timeout
diff --git a/Misc/NEWS.d/next/Library/2024-07-08-03-45-34.gh-issue-121474.NsvrUN.rst b/Misc/NEWS.d/next/Library/2024-07-08-03-45-34.gh-issue-121474.NsvrUN.rst
new file mode 100644
index 0000000..605f30d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-07-08-03-45-34.gh-issue-121474.NsvrUN.rst
@@ -0,0 +1,2 @@
+Fix missing sanity check for ``parties`` arg in :class:`threading.Barrier`
+constructor. Patch by Clinton Christian (pygeek).