Fix CurlAsyncHTTPClient cause memory leak with `force_instance=True`

The CurlAsyncHTTPClient will cause memory leak when set `force_instance=True`,
because the `self._multi` and `self._force_timeout_callback` hold some methods
that belong the instance of `CurlAsyncHTTPClient`, it will cause circular reference.

diff --git a/tornado/curl_httpclient.py b/tornado/curl_httpclient.py
index eef4a17a6b4a7e6e30c2db0ab5b1f44c2791ebea..554710ee4dd56b090c0cdb7b09bc36432fcb8898 100644 (file)
--- a/tornado/curl_httpclient.py
+++ b/tornado/curl_httpclient.py
@@ -74,6 +74,12 @@ class CurlAsyncHTTPClient(AsyncHTTPClient):
         self._multi.close()
         super(CurlAsyncHTTPClient, self).close()
 
+        # Set below properties to None to reduce the reference count of current
+        # instance, because those properties hold some methods of current
+        # instance that will case circular reference.
+        self._force_timeout_callback = None
+        self._multi = None
+
     def fetch_impl(self, request, callback):
         self._requests.append((request, callback))
         self._process_queue()