Make polling a cursor that's not in an async query raise an exception.

If there is an asynchronous query, polling a cursor that did not
initiate it will raise an exception. Polling while there is no
asynchronous query underway still works, because the user needs to
have a way to get asynchronous NOTIFYs.

psycopg/cursor_type.c

@@ -1480,6 +1480,12 @@ psyco_curs_poll(cursorObject *self)
 {
     EXC_IF_CURS_CLOSED(self);
 
+    if (self->conn->async_cursor != NULL &&
+        self->conn->async_cursor != (PyObject *) self) {
+        PyErr_SetString(ProgrammingError, "poll with wrong cursor");
+        return NULL;
+    }
+
     Dprintf("curs_poll: polling with status %d", self->conn->async_status);
 
     if (self->conn->async_status == ASYNC_WRITE) {

tests/test_async.py

@@ -299,7 +299,6 @@ class AsyncTests(unittest.TestCase):
         self.assert_(not conn.issync())
         conn.close()
 
-
     def test_flush_on_write(self):
         # a very large query requires a flush loop to be sent to the backend
         curs = self.conn.cursor()
@@ -315,6 +314,34 @@ class AsyncTests(unittest.TestCase):
 
         self.fail("sending a large query didn't trigger block on write.")
 
+    def test_sync_poll(self):
+        cur = self.sync_conn.cursor()
+        # polling a sync cursor works
+        cur.poll()
+
+    def test_async_poll_wrong_cursor(self):
+        cur1 = self.conn.cursor()
+        cur2 = self.conn.cursor()
+        cur1.execute("select 1")
+
+        # polling a cursor that's not currently executing is an error
+        self.assertRaises(psycopg2.ProgrammingError, cur2.poll)
+
+        self.wait_for_query(cur1)
+        self.assertEquals(cur1.fetchone()[0], 1)
+
+    def test_async_fetch_wrong_cursor(self):
+        cur1 = self.conn.cursor()
+        cur2 = self.conn.cursor()
+        cur1.execute("select 1")
+
+        self.wait_for_query(cur1)
+        self.assertFalse(self.conn.executing())
+        # fetching from a cursor with no results is an error
+        self.assertRaises(psycopg2.ProgrammingError, cur2.fetchone)
+        # fetching from the correct cursor works
+        self.assertEquals(cur1.fetchone()[0], 1)
+
 def test_suite():
     return unittest.TestLoader().loadTestsFromName(__name__)