diff -r f6c4c178da56 Modules/selectmodule.c
--- a/Modules/selectmodule.c	Sun Nov 11 14:01:23 2012 +0100
+++ b/Modules/selectmodule.c	Sun Nov 11 23:48:21 2012 +0200
@@ -315,7 +315,8 @@
 typedef struct {
     PyObject_HEAD
     PyObject *dict;
-    int ufd_uptodate;
+    int tag;
+    int ufd_tag;
     int ufd_len;
     struct pollfd *ufds;
 } pollObject;
@@ -347,7 +348,7 @@
         self->ufds[i].events = (short)PyInt_AsLong(value);
         i++;
     }
-    self->ufd_uptodate = 1;
+    self->ufd_tag = self->tag;
     return 1;
 }
 
@@ -388,7 +389,7 @@
     if (err < 0)
         return NULL;
 
-    self->ufd_uptodate = 0;
+    self->tag += 1;
 
     Py_INCREF(Py_None);
     return Py_None;
@@ -435,7 +436,7 @@
     if (err < 0)
         return NULL;
 
-    self->ufd_uptodate = 0;
+    self->tag += 1;
 
     Py_INCREF(Py_None);
     return Py_None;
@@ -469,7 +470,7 @@
     }
 
     Py_DECREF(key);
-    self->ufd_uptodate = 0;
+    self->tag += 1;
 
     Py_INCREF(Py_None);
     return Py_None;
@@ -484,8 +485,9 @@
 poll_poll(pollObject *self, PyObject *args)
 {
     PyObject *result_list = NULL, *tout = NULL;
-    int timeout = 0, poll_result, i, j;
+    int timeout = 0, poll_result, i, j, ufd_tag, ufd_len;
     PyObject *value = NULL, *num = NULL;
+    struct pollfd *ufds;
 
     if (!PyArg_UnpackTuple(args, "poll", 0, 1, &tout)) {
         return NULL;
@@ -510,29 +512,32 @@
     }
 
     /* Ensure the ufd array is up to date */
-    if (!self->ufd_uptodate)
+    if (!self->ufds || (self->ufd_tag != self->tag))
         if (update_ufd_array(self) == 0)
             return NULL;
 
+    ufd_tag = self->ufd_tag;
+    ufd_len = self->ufd_len;
+    ufds = self->ufds;
+    self->ufds = NULL;
+
     /* call poll() */
     Py_BEGIN_ALLOW_THREADS
-    poll_result = poll(self->ufds, self->ufd_len, timeout);
+    poll_result = poll(ufds, ufd_len, timeout);
     Py_END_ALLOW_THREADS
 
     if (poll_result < 0) {
         PyErr_SetFromErrno(SelectError);
-        return NULL;
+        goto done;
     }
 
     /* build the result list */
 
     result_list = PyList_New(poll_result);
-    if (!result_list)
-        return NULL;
-    else {
+    if (result_list) {
         for (i = 0, j = 0; j < poll_result; j++) {
             /* skip to the next fired descriptor */
-            while (!self->ufds[i].revents) {
+            while (!ufds[i].revents) {
                 i++;
             }
             /* if we hit a NULL return, set value to NULL
@@ -541,7 +546,7 @@
             value = PyTuple_New(2);
             if (value == NULL)
                 goto error;
-            num = PyInt_FromLong(self->ufds[i].fd);
+            num = PyInt_FromLong(ufds[i].fd);
             if (num == NULL) {
                 Py_DECREF(value);
                 goto error;
@@ -552,7 +557,7 @@
                is a 16-bit short, and IBM assigned POLLNVAL
                to be 0x8000, so the conversion to int results
                in a negative number. See SF bug #923315. */
-            num = PyInt_FromLong(self->ufds[i].revents & 0xffff);
+            num = PyInt_FromLong(ufds[i].revents & 0xffff);
             if (num == NULL) {
                 Py_DECREF(value);
                 goto error;
@@ -565,11 +570,19 @@
             i++;
         }
     }
+  done:
+    if (self->ufds == NULL && self->tag == ufd_tag) {
+        self->ufds = ufds;
+        self->ufd_tag = ufd_tag;
+        self->ufd_len = ufd_len;
+    } else {
+        PyMem_FREE(ufds);
+    }
     return result_list;
 
   error:
-    Py_DECREF(result_list);
-    return NULL;
+    Py_CLEAR(result_list);
+    goto done;
 }
 
 static PyMethodDef poll_methods[] = {
@@ -591,9 +604,10 @@
     self = PyObject_New(pollObject, &poll_Type);
     if (self == NULL)
         return NULL;
-    /* ufd_uptodate is a Boolean, denoting whether the
-       array pointed to by ufds matches the contents of the dictionary. */
-    self->ufd_uptodate = 0;
+    /* tag is an int which is incremented every time the dictionary is
+       updated; ufd_tag is the tag that currently belong to the ufds array
+       if ufds != NULL && tag == ufd_tag, then ufds is up-to-date */
+    self->tag = 0;
     self->ufds = NULL;
     self->dict = PyDict_New();
     if (self->dict == NULL) {