semaphore: Don't hog a semaphore if someone else is waiting for ittm

https://github.com/eventlet/eventlet/issues/136
https://github.com/eventlet/eventlet/pull/163

(comment by Sergey Shepelev) _waiters is now deque, watch out for O(N) acquire()

1 files changed, 20 insertions, 1 deletions

diff --git a/tests/semaphore_test.py b/tests/semaphore_test.py
index 1316330..ced9136 100644
--- a/tests/semaphore_test.py
+++ b/tests/semaphore_test.py
@@ -45,5 +45,24 @@ class TestSemaphore(LimitedTestCase):
         self.assertRaises(ValueError, sem.acquire, blocking=False, timeout=1)
 
 
+def test_semaphore_contention():
+    g_mutex = semaphore.Semaphore()
+    counts = [0, 0]
+
+    def worker(no):
+        while min(counts) < 200:
+            with g_mutex:
+                counts[no - 1] += 1
+                eventlet.sleep(0.001)
+
+    t1 = eventlet.spawn(worker, no=1)
+    t2 = eventlet.spawn(worker, no=2)
+    eventlet.sleep(0.5)
+    t1.kill()
+    t2.kill()
+
+    assert abs(counts[0] - counts[1]) < int(min(counts) * 0.1), counts
+
+
 if __name__ == '__main__':
-    unittest.main()
+    unittest.main()
\ No newline at end of file