Merge pull request #322 from Pylons/connection-overflow-warning

warn when the server stops listening for connections because it's in overflow

3 files changed, 43 insertions, 1 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index f4d1acc..c62602e 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -3,6 +3,12 @@
 
 - Drop Python 2.7 support
 
+- The server now issues warning output when it there are enough open
+  connections (controlled by "connection_limit"), that it is no longer
+  accepting new connections. This situation was previously difficult to
+  diagnose.
+  See https://github.com/Pylons/waitress/pull/322
+
 1.4.4 (2020-06-01)
 ------------------
 
diff --git a/src/waitress/server.py b/src/waitress/server.py
index b053c69..b37980e 100644
--- a/src/waitress/server.py
+++ b/src/waitress/server.py
@@ -179,6 +179,7 @@ class BaseWSGIServer(wasyncore.dispatcher):
     next_channel_cleanup = 0
     socketmod = socket  # test shim
     asyncore = wasyncore  # test shim
+    in_connection_overflow = False
 
     def __init__(
         self,
@@ -296,7 +297,28 @@ class BaseWSGIServer(wasyncore.dispatcher):
         if now >= self.next_channel_cleanup:
             self.next_channel_cleanup = now + self.adj.cleanup_interval
             self.maintenance(now)
-        return self.accepting and len(self._map) < self.adj.connection_limit
+
+        if self.accepting:
+            if (
+                not self.in_connection_overflow
+                and len(self._map) >= self.adj.connection_limit
+            ):
+                self.in_connection_overflow = True
+                self.logger.warning(
+                    "total open connections reached the connection limit, "
+                    "no longer accepting new connections"
+                )
+            elif (
+                self.in_connection_overflow
+                and len(self._map) < self.adj.connection_limit
+            ):
+                self.in_connection_overflow = False
+                self.logger.info(
+                    "total open connections dropped below the connection limit, "
+                    "listening again"
+                )
+            return not self.in_connection_overflow
+        return False
 
     def writable(self):
         return False
diff --git a/tests/test_server.py b/tests/test_server.py
index 05f6b4e..508b382 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -185,6 +185,7 @@ class TestWSGIServer(unittest.TestCase):
         inst.adj = DummyAdj
         inst._map = {"a": 1, "b": 2}
         self.assertFalse(inst.readable())
+        self.assertTrue(inst.in_connection_overflow)
 
     def test_readable_maplen_lt_connection_limit(self):
         inst = self._makeOneWithMap()
@@ -192,6 +193,19 @@ class TestWSGIServer(unittest.TestCase):
         inst.adj = DummyAdj
         inst._map = {}
         self.assertTrue(inst.readable())
+        self.assertFalse(inst.in_connection_overflow)
+
+    def test_readable_maplen_toggles_connection_overflow(self):
+        inst = self._makeOneWithMap()
+        inst.accepting = True
+        inst.adj = DummyAdj
+        inst._map = {"a": 1, "b": 2}
+        self.assertFalse(inst.in_connection_overflow)
+        self.assertFalse(inst.readable())
+        self.assertTrue(inst.in_connection_overflow)
+        inst._map = {}
+        self.assertTrue(inst.readable())
+        self.assertFalse(inst.in_connection_overflow)
 
     def test_readable_maintenance_false(self):
         import time