Fix race condition in PyStringMap keys method [GH-156]

If the map was modified during a call to keys(), the keyset would change
size and cause an ArrayIndexOutOfBoundsException. This creates a copy of
the keyset and uses that throughout the method.

--HG--
extra : amend_source : 025dd98595b444af0c4ffb67ae4bd4252fb752b4

NEWS

@@ -8,6 +8,7 @@ https://github.com/jythontools/jython
 
 Jython 2.7.2b4
   Bugs fixed
+    - [ GH-156 ] Race condition in PyStringMap keys method
     - [ 2862 ] Jython fails on Linux for normal user when installed by root
 
 Jython 2.7.2b3

src/org/python/core/PyStringMap.java

@@ -637,9 +637,10 @@ public PyList keys() {
 
     @ExposedMethod(doc = BuiltinDocs.dict_keys_doc)
     final PyList stringmap_keys() {
-        PyObject[] keyArray = new PyObject[table.size()];
+        Object[] keys = table.keySet().toArray();
+        PyObject[] keyArray = new PyObject[keys.length];
         int i = 0;
-        for (Object key : table.keySet()) {
+        for (Object key : keys) {
             keyArray[i++] = keyToPy(key);
         }
         return new PyList(keyArray);