gh-121474: Add threading.Barrier parties arg sanity check.

Lib/test/lock_tests.py

@@ -1013,6 +1013,10 @@ def multipass(self, results, n):
         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

Lib/threading.py

@@ -689,6 +689,8 @@ def __init__(self, parties, action=None, timeout=None):
         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

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).