Changed the automatic garbage collection when opening a connection to only

apply the garbage collections on those connections in the pool that are
closed. (This fixed issue 113932.)

NEWS.txt

@@ -62,6 +62,10 @@ Connection management
   and/or store limited resources (such as RDB connections) in connection
   caches may benefit.
 
+- (3.7.0c1) Changed the automatic garbage collection when opening a connection
+  to only apply the garbage collections on those connections in the pool that
+  are closed. (This fixed issue 113932.)
+
 DemoStorage
 -----------
 

src/ZODB/DB.py

@@ -145,9 +145,17 @@ class _ConnectionPool(object):
             assert result in self.all
         return result
 
-    # For every live connection c, invoke f(c).
-    def map(self, f):
-        self.all.map(f)
+    def map(self, f, open_connections=True):
+        """For every live connection c, invoke f(c).
+
+        If `open_connections` is false then only call f(c) on closed
+        connections.
+
+        """
+        if open_connections:
+            self.all.map(f)
+        else:
+            map(f, self.available)
 
 class DB(object):
     """The Object Database
@@ -304,12 +312,17 @@ class DB(object):
         finally:
             self._r()
 
-    # Call f(c) for all connections c in all pools in all versions.
-    def _connectionMap(self, f):
+    def _connectionMap(self, f, open_connections=True):
+        """Call f(c) for all connections c in all pools in all versions.
+
+        If `open_connections` is false then f(c) is only called on closed
+        connections.
+
+        """
         self._a()
         try:
             for pool in self._pools.values():
-                pool.map(f)
+                pool.map(f, open_connections=open_connections)
         finally:
             self._r()
 
@@ -548,7 +561,7 @@ class DB(object):
             result.open(transaction_manager, mvcc, synch)
 
             # A good time to do some cache cleanup.
-            self._connectionMap(lambda c: c.cacheGC())
+            self._connectionMap(lambda c: c.cacheGC(), open_connections=False)
 
             return result
 

src/ZODB/tests/test_cache.py

@@ -51,6 +51,9 @@ class RegularObject(Persistent):
 
     init = classmethod(init)
 
+class PersistentObject(Persistent):
+    pass
+
 class CacheTests:
 
     def test_cache(self):
@@ -204,6 +207,35 @@ class CacheTests:
         4
         """
 
+    def test_gc_on_open_connections(self):
+        r"""Test that automatic GC is not applied to open connections.
+
+        This test (and the corresponding fix) was introduced because of bug
+        report 113923.
+
+        We start with a persistent object and add a list attribute::
+
+            >>> db = databaseFromString("<zodb>\n"
+            ...                         "cache-size 0\n"
+            ...                         "<mappingstorage/>\n"
+            ...                         "</zodb>")
+            >>> cn1 = db.open()
+            >>> r = cn1.root()
+            >>> r['ob'] = PersistentObject()
+            >>> r['ob'].l = []
+            >>> transaction.commit()
+
+        Now, let's modify the object in a way that doesn't get noticed. Then,
+        we open another connection which triggers automatic garbage
+        connection. After that, the object should not have been ghostified::
+
+            >>> r['ob'].l.append(1)
+            >>> cn2 = db.open()
+            >>> r['ob'].l
+            [1]
+
+        """
+
 
 def test_suite():
     return doctest.DocTestSuite()