Issue #6915: Under Windows, os.listdir() didn't release the Global

Interpreter Lock around all system calls.  Original patch by Ryan Kelly.

Misc/ACKS

@@ -419,6 +419,7 @@ Jacob Kaplan-Moss
 Lou Kates
 Hiroaki Kawai
 Sebastien Keim
+Ryan Kelly
 Robert Kern
 Randall Kern
 Magnus Kessler

Misc/NEWS

@@ -30,6 +30,9 @@ Core and Builtins
 Extensions
 ----------
 
+- Issue #6915: Under Windows, os.listdir() didn't release the Global
+  Interpreter Lock around all system calls.  Original patch by Ryan Kelly.
+
 - Issue #8524: Add a detach() method to socket objects, so as to put the
   socket into the closed state without closing the underlying file
   descriptor.

Modules/posixmodule.c

@@ -2353,7 +2353,9 @@ posix_listdir(PyObject *self, PyObject *args)
             free(wnamebuf);
             return NULL;
         }
+        Py_BEGIN_ALLOW_THREADS
         hFindFile = FindFirstFileW(wnamebuf, &wFileData);
+        Py_END_ALLOW_THREADS
         if (hFindFile == INVALID_HANDLE_VALUE) {
             int error = GetLastError();
             if (error == ERROR_FILE_NOT_FOUND) {
@@ -2430,7 +2432,9 @@ posix_listdir(PyObject *self, PyObject *args)
     if ((d = PyList_New(0)) == NULL)
         return NULL;
 
+    Py_BEGIN_ALLOW_THREADS
     hFindFile = FindFirstFile(namebuf, &FileData);
+    Py_END_ALLOW_THREADS
     if (hFindFile == INVALID_HANDLE_VALUE) {
         int error = GetLastError();
         if (error == ERROR_FILE_NOT_FOUND)