Index: PC/winreg.c
===================================================================
--- PC/winreg.c	(revision 81396)
+++ PC/winreg.c	(working copy)
@@ -1096,7 +1096,14 @@
     int index;
     long rc;
     PyObject *retStr;
-    wchar_t tmpbuf[256]; /* max key name length is 255 */
+
+    /* The Windows docs claim that the max key name length is 255
+     * characters, plus a terminating nul character.  However,
+     * empirical testing demonstrates that it is possible to
+     * create a 256 character key that is missing the terminating
+     * nul.  RegEnumKeyEx requires a 257 character buffer to
+     * retrieve such a key name. */
+    wchar_t tmpbuf[257];
     DWORD len = sizeof(tmpbuf); /* includes NULL terminator */
 
     if (!PyArg_ParseTuple(args, "Oi:EnumKey", &obKey, &index))
@@ -1123,8 +1130,8 @@
     long rc;
     wchar_t *retValueBuf;
     BYTE *retDataBuf;
-    DWORD retValueSize;
-    DWORD retDataSize;
+    DWORD retValueSize, bufValueSize;
+    DWORD retDataSize, bufDataSize;
     DWORD typ;
     PyObject *obData;
     PyObject *retVal;
@@ -1142,6 +1149,8 @@
                                                    "RegQueryInfoKey");
     ++retValueSize;    /* include null terminators */
     ++retDataSize;
+    bufDataSize = retDataSize;
+    bufValueSize = retValueSize;
     retValueBuf = (wchar_t *)PyMem_Malloc(sizeof(wchar_t) * retValueSize);
     if (retValueBuf == NULL)
         return PyErr_NoMemory();
@@ -1151,17 +1160,34 @@
         return PyErr_NoMemory();
     }
 
-    Py_BEGIN_ALLOW_THREADS
-    rc = RegEnumValueW(hKey,
-                      index,
-                      retValueBuf,
-                      &retValueSize,
-                      NULL,
-                      &typ,
-                      retDataBuf,
-                      &retDataSize);
-    Py_END_ALLOW_THREADS
+    while (1) {
+        wchar_t *tmp;
+        Py_BEGIN_ALLOW_THREADS
+        rc = RegEnumValueW(hKey,
+                  index,
+                  retValueBuf,
+                  &retValueSize,
+                  NULL,
+                  &typ,
+                  (BYTE *)retDataBuf,
+                  &retDataSize);
+        Py_END_ALLOW_THREADS
 
+        if (rc != ERROR_MORE_DATA)
+            break;
+
+        bufDataSize *= 2;
+        tmp = (char *)PyMem_Realloc(retDataBuf, bufDataSize);
+        if (tmp == NULL) {
+            PyErr_NoMemory();
+            retVal = NULL;
+            goto fail;
+        }
+        retDataBuf = tmp;
+        retDataSize = bufDataSize;
+        retValueSize = bufValueSize;
+    }
+
     if (rc != ERROR_SUCCESS) {
         retVal = PyErr_SetFromWindowsErrWithFunction(rc,
                                                      "PyRegEnumValue");
@@ -1317,23 +1343,44 @@
     long rc;
     PyObject *retStr;
     wchar_t *retBuf;
-    long bufSize = 0;
+    DWORD bufSize = 0;
+    DWORD retSize = 0;
+    wchar_t *tmp;
 
     if (!PyArg_ParseTuple(args, "OZ:QueryValue", &obKey, &subKey))
         return NULL;
 
     if (!PyHKEY_AsHKEY(obKey, &hKey, FALSE))
         return NULL;
-    if ((rc = RegQueryValueW(hKey, subKey, NULL, &bufSize))
-        != ERROR_SUCCESS)
+
+    rc = RegQueryValueW(hKey, subKey, NULL, &retSize);
+    if (rc == ERROR_MORE_DATA)
+        retSize = 256;
+    else if (rc != ERROR_SUCCESS)
         return PyErr_SetFromWindowsErrWithFunction(rc,
                                                    "RegQueryValue");
-    retBuf = (wchar_t *)PyMem_Malloc(bufSize);
+
+    bufSize = retSize;
+    retBuf = (wchar_t *) PyMem_Malloc(bufSize);
     if (retBuf == NULL)
         return PyErr_NoMemory();
 
-    if ((rc = RegQueryValueW(hKey, subKey, retBuf, &bufSize))
-        != ERROR_SUCCESS) {
+    while (1) {
+        retSize = bufSize;
+        rc = RegQueryValueW(hKey, subKey, retBuf, &retSize);
+        if (rc != ERROR_MORE_DATA)
+            break;
+
+        bufSize *= 2;
+        tmp = (wchar_t *) PyMem_Realloc(retBuf, bufSize);
+        if (tmp == NULL) {
+            PyMem_Free(retBuf);
+            return PyErr_NoMemory();
+        }
+        retBuf = tmp;
+    }
+
+    if (rc != ERROR_SUCCESS) {
         PyMem_Free(retBuf);
         return PyErr_SetFromWindowsErrWithFunction(rc,
                                                    "RegQueryValue");
@@ -1352,8 +1399,8 @@
     wchar_t *valueName;
 
     long rc;
-    BYTE *retBuf;
-    DWORD bufSize = 0;
+    BYTE *retBuf, *tmp;
+    DWORD bufSize = 0, retSize;
     DWORD typ;
     PyObject *obData;
     PyObject *result;
@@ -1363,18 +1410,34 @@
 
     if (!PyHKEY_AsHKEY(obKey, &hKey, FALSE))
         return NULL;
-    if ((rc = RegQueryValueExW(hKey, valueName,
-                              NULL, NULL, NULL,
-                              &bufSize))
-        != ERROR_SUCCESS)
+
+    rc = RegQueryValueExW(hKey, valueName, NULL, NULL, NULL, &bufSize);
+    if (rc == ERROR_MORE_DATA)
+        bufSize = 256;
+    else if (rc != ERROR_SUCCESS)
         return PyErr_SetFromWindowsErrWithFunction(rc,
                                                    "RegQueryValueEx");
     retBuf = (BYTE *)PyMem_Malloc(bufSize);
     if (retBuf == NULL)
         return PyErr_NoMemory();
-    if ((rc = RegQueryValueExW(hKey, valueName, NULL,
-                              &typ, retBuf, &bufSize))
-        != ERROR_SUCCESS) {
+
+    while (1) {
+        retSize = bufSize;
+        rc = RegQueryValueExW(hKey, valueName, NULL, &typ,
+                             (BYTE *)retBuf, &retSize);
+        if (rc != ERROR_MORE_DATA)
+            break;
+
+        bufSize *= 2;
+        tmp = (char *) PyMem_Realloc(retBuf, bufSize);
+        if (tmp == NULL) {
+            PyMem_Free(retBuf);
+            return PyErr_NoMemory();
+        }
+       retBuf = tmp;
+    }
+
+    if (rc != ERROR_SUCCESS) {
         PyMem_Free(retBuf);
         return PyErr_SetFromWindowsErrWithFunction(rc,
                                                    "RegQueryValueEx");
Index: Lib/test/test_winreg.py
===================================================================
--- Lib/test/test_winreg.py	(revision 81396)
+++ Lib/test/test_winreg.py	(working copy)
@@ -5,6 +5,7 @@
 import os, sys
 import unittest
 from test import support
+threading = support.import_module("threading")
 from platform import machine
 
 # Do this first so test will be skipped if module doesn't exist
@@ -227,6 +228,58 @@
         except WindowsError:
             self.assertEqual(h.handle, 0)
 
+    def test_changing_value(self):
+        # Issue2810: A race condition in 2.6 and 3.1 may cause
+        # EnumValue or QueryValue to throw "WindowsError: More data is
+        # available"
+        done = False
+
+        class VeryActiveThread(threading.Thread):
+            def run(self):
+                with CreateKey(HKEY_CURRENT_USER, test_key_name) as key:
+                    use_short = True
+                    long_string = 'x'*2000
+                    while not done:
+                        s = 'x' if use_short else long_string
+                        use_short = not use_short
+                        SetValue(key, 'changing_value', REG_SZ, s)
+
+        thread = VeryActiveThread()
+        thread.start()
+        try:
+            with CreateKey(HKEY_CURRENT_USER,
+                           test_key_name+'\\changing_value') as key:
+                for _ in range(1000):
+                    num_subkeys, num_values, t = QueryInfoKey(key)
+                    for i in range(num_values):
+                        name = EnumValue(key, i)
+                        QueryValue(key, name[0])
+        finally:
+            done = True
+            thread.join()
+            DeleteKey(HKEY_CURRENT_USER, test_key_name+'\\changing_value')
+            DeleteKey(HKEY_CURRENT_USER, test_key_name)
+
+    def test_long_key(self):
+        # Issue2810, in 2.6 and 3.1 when the key name was exactly 256
+        # characters, EnumKey threw "WindowsError: More data is
+        # available"
+        name = 'x'*256
+        try:
+            with CreateKey(HKEY_CURRENT_USER, test_key_name) as key:
+                SetValue(key, name, REG_SZ, 'x')
+                num_subkeys, num_values, t = QueryInfoKey(key)
+                EnumKey(key, 0)
+        finally:
+            DeleteKey(HKEY_CURRENT_USER, '\\'.join((test_key_name, name)))
+            DeleteKey(HKEY_CURRENT_USER, test_key_name)
+
+    def test_dynamic_key(self):
+        # Issue2810, when the value is dynamically generated, these
+        # throw "WindowsError: More data is available" in 2.6 and 3.1
+        EnumValue(HKEY_PERFORMANCE_DATA, 0)
+        QueryValueEx(HKEY_PERFORMANCE_DATA, None)
+
     # Reflection requires XP x64/Vista at a minimum. XP doesn't have this stuff
     # or DeleteKeyEx so make sure their use raises NotImplementedError
     @unittest.skipUnless(WIN_VER < (5, 2), "Requires Windows XP")