* Use weakref's of DBCursor objects for the iterator cursors to avoid a

  memory leak that would've occurred for all iterators that were
  destroyed before having iterated until they raised StopIteration.

* Simplify some code.

* Add new test cases to check for the memleak and ensure that mixing
  iteration with modification of the values for existing keys works.

2 files changed, 121 insertions, 50 deletions

diff --git a/Lib/bsddb/__init__.py b/Lib/bsddb/__init__.py
index 778ad29..99499c5 100644
--- a/Lib/bsddb/__init__.py
+++ b/Lib/bsddb/__init__.py
@@ -67,77 +67,76 @@ import sys
 if sys.version >= '2.3':
     exec """
 import UserDict
+from weakref import ref
 class _iter_mixin(UserDict.DictMixin):
+    def _make_iter_cursor(self):
+        cur = self.db.cursor()
+        key = id(cur)
+        self._cursor_refs[key] = ref(cur, self._gen_cref_cleaner(key))
+        return cur
+
+    def _gen_cref_cleaner(self, key):
+        # use generate the function for the weakref callback here
+        # to ensure that we do not hold a strict reference to cur
+        # in the callback.
+        return lambda ref: self._cursor_refs.pop(key, None)
+
     def __iter__(self):
         try:
-            cur = self.db.cursor()
-            self._iter_cursors[str(cur)] = cur
+            cur = self._make_iter_cursor()
+
+            # FIXME-20031102-greg: race condition.  cursor could
+            # be closed by another thread before this call.
 
             # since we're only returning keys, we call the cursor
             # methods with flags=0, dlen=0, dofs=0
-            curkey = cur.first(0,0,0)[0]
-            yield curkey
+            key = cur.first(0,0,0)[0]
+            yield key
 
             next = cur.next
             while 1:
                 try:
-                    curkey = next(0,0,0)[0]
-                    yield curkey
+                    key = next(0,0,0)[0]
+                    yield key
                 except _bsddb.DBCursorClosedError:
-                    # our cursor object was closed since we last yielded
-                    # create a new one and attempt to reposition to the
-                    # right place
-                    cur = self.db.cursor()
-                    self._iter_cursors[str(cur)] = cur
+                    cur = self._make_iter_cursor()
                     # FIXME-20031101-greg: race condition.  cursor could
-                    # be closed by another thread before this set call.
-                    try:
-                        cur.set(curkey,0,0,0)
-                    except _bsddb.DBCursorClosedError:
-                        # halt iteration on race condition...
-                        raise _bsddb.DBNotFoundError
+                    # be closed by another thread before this call.
+                    cur.set(key,0,0,0)
                     next = cur.next
         except _bsddb.DBNotFoundError:
-            try:
-                del self._iter_cursors[str(cur)]
-            except KeyError:
-                pass
+            return
+        except _bsddb.DBCursorClosedError:
+            # the database was modified during iteration.  abort.
             return
 
     def iteritems(self):
         try:
-            cur = self.db.cursor()
-            self._iter_cursors[str(cur)] = cur
+            cur = self._make_iter_cursor()
+
+            # FIXME-20031102-greg: race condition.  cursor could
+            # be closed by another thread before this call.
 
             kv = cur.first()
-            curkey = kv[0]
+            key = kv[0]
             yield kv
 
             next = cur.next
             while 1:
                 try:
                     kv = next()
-                    curkey = kv[0]
+                    key = kv[0]
                     yield kv
                 except _bsddb.DBCursorClosedError:
-                    # our cursor object was closed since we last yielded
-                    # create a new one and attempt to reposition to the
-                    # right place
-                    cur = self.db.cursor()
-                    self._iter_cursors[str(cur)] = cur
+                    cur = self._make_iter_cursor()
                     # FIXME-20031101-greg: race condition.  cursor could
-                    # be closed by another thread before this set call.
-                    try:
-                        cur.set(curkey,0,0,0)
-                    except _bsddb.DBCursorClosedError:
-                        # halt iteration on race condition...
-                        raise _bsddb.DBNotFoundError
+                    # be closed by another thread before this call.
+                    cur.set(key,0,0,0)
                     next = cur.next
         except _bsddb.DBNotFoundError:
-            try:
-                del self._iter_cursors[str(cur)]
-            except KeyError:
-                pass
+            return
+        except _bsddb.DBCursorClosedError:
+            # the database was modified during iteration.  abort.
             return
 """
 else:
@@ -159,7 +158,7 @@ class _DBWithCursor(_iter_mixin):
         # thread while doing a put or delete in another thread.  The
         # reason is that _checkCursor and _closeCursors are not atomic
         # operations.  Doing our own locking around self.dbc,
-        # self.saved_dbc_key and self._iter_cursors could prevent this.
+        # self.saved_dbc_key and self._cursor_refs could prevent this.
         # TODO: A test case demonstrating the problem needs to be written.
 
         # self.dbc is a DBCursor object used to implement the
@@ -169,15 +168,11 @@ class _DBWithCursor(_iter_mixin):
 
         # a collection of all DBCursor objects currently allocated
         # by the _iter_mixin interface.
-        self._iter_cursors = {}
-
+        self._cursor_refs = {}
 
     def __del__(self):
         self.close()
 
-    def _get_dbc(self):
-        return self.dbc
-
     def _checkCursor(self):
         if self.dbc is None:
             self.dbc = self.db.cursor()
@@ -197,7 +192,10 @@ class _DBWithCursor(_iter_mixin):
                 self.saved_dbc_key = c.current(0,0,0)[0]
             c.close()
             del c
-        map(lambda c: c.close(), self._iter_cursors.values())
+        for cref in self._cursor_refs.values():
+            c = cref()
+            if c is not None:
+                c.close()
 
     def _checkOpen(self):
         if self.db is None:
diff --git a/Lib/test/test_bsddb.py b/Lib/test/test_bsddb.py
index ff8c355..1ec4801 100755
--- a/Lib/test/test_bsddb.py
+++ b/Lib/test/test_bsddb.py
@@ -3,6 +3,7 @@
    Adapted to unittest format and expanded scope by Raymond Hettinger
 """
 import os, sys
+import copy
 import bsddb
 import dbhash # Just so we know it's imported
 import unittest
@@ -64,6 +65,56 @@ class TestBSDDB(unittest.TestCase):
         self.assertSetEquals(d.itervalues(), f.itervalues())
         self.assertSetEquals(d.iteritems(), f.iteritems())
 
+    def test_iter_while_modifying_values(self):
+        if not hasattr(self.f, '__iter__'):
+            return
+
+        di = iter(self.d)
+        while 1:
+            try:
+                key = di.next()
+                self.d[key] = 'modified '+key
+            except StopIteration:
+                break
+
+        # it should behave the same as a dict.  modifying values
+        # of existing keys should not break iteration.  (adding
+        # or removing keys should)
+        fi = iter(self.f)
+        while 1:
+            try:
+                key = fi.next()
+                self.f[key] = 'modified '+key
+            except StopIteration:
+                break
+
+        self.test_mapping_iteration_methods()
+
+    def test_iteritems_while_modifying_values(self):
+        if not hasattr(self.f, 'iteritems'):
+            return
+
+        di = self.d.iteritems()
+        while 1:
+            try:
+                k, v = di.next()
+                self.d[k] = 'modified '+v
+            except StopIteration:
+                break
+
+        # it should behave the same as a dict.  modifying values
+        # of existing keys should not break iteration.  (adding
+        # or removing keys should)
+        fi = self.f.iteritems()
+        while 1:
+            try:
+                k, v = fi.next()
+                self.f[k] = 'modified '+v
+            except StopIteration:
+                break
+
+        self.test_mapping_iteration_methods()
+
     def test_first_next_looping(self):
         items = [self.f.first()]
         for i in xrange(1, len(self.f)):
@@ -111,15 +162,16 @@ class TestBSDDB(unittest.TestCase):
         # the cursor's read lock will deadlock the write lock request..
 
         # test the iterator interface (if present)
-        if hasattr(self, 'iteritems'):
+        if hasattr(self.f, 'iteritems'):
             if debug: print "D"
-            k,v = self.f.iteritems()
+            i = self.f.iteritems()
+            k,v = i.next()
             if debug: print "E"
             self.f[k] = "please don't deadlock"
             if debug: print "F"
             while 1:
                 try:
-                    k,v = self.f.iteritems()
+                    k,v = i.next()
                 except StopIteration:
                     break
             if debug: print "F2"
@@ -144,6 +196,27 @@ class TestBSDDB(unittest.TestCase):
         self.f[k] = "be gone with ye deadlocks"
         self.assert_(self.f[k], "be gone with ye deadlocks")
 
+    def test_for_cursor_memleak(self):
+        if not hasattr(self.f, 'iteritems'):
+            return
+
+        # do the bsddb._DBWithCursor _iter_mixin internals leak cursors?
+        nc1 = len(self.f._cursor_refs)
+        # create iterator
+        i = self.f.iteritems()
+        nc2 = len(self.f._cursor_refs)
+        # use the iterator (should run to the first yeild, creating the cursor)
+        k, v = i.next()
+        nc3 = len(self.f._cursor_refs)
+        # destroy the iterator; this should cause the weakref callback
+        # to remove the cursor object from self.f._cursor_refs
+        del i
+        nc4 = len(self.f._cursor_refs)
+
+        self.assertEqual(nc1, nc2)
+        self.assertEqual(nc1, nc4)
+        self.assert_(nc3 == nc1+1)
+
     def test_popitem(self):
         k, v = self.f.popitem()
         self.assert_(k in self.d)