bpo-31249: Fix ref cycle in ThreadPoolExecutor (#3178)

vstinner · web-flow · commit bc6131537705 · 2017-08-22T16:50:42.000+02:00
* bpo-31249: Fix ref cycle in ThreadPoolExecutor concurrent.futures: WorkItem.run() used by ThreadPoolExecutor now breaks a reference cycle between an exception object and the WorkItem object. ThreadPoolExecutor.shutdown() now also clears its threads set. * shutdown() now only clears threads if wait is true. * Revert changes on shutdown()
diff --git a/Lib/concurrent/futures/thread.py b/Lib/concurrent/futures/thread.py
@@ -54,8 +54,10 @@ def run(self):
 
         try:
             result = self.fn(*self.args, **self.kwargs)
-        except BaseException as e:
-            self.future.set_exception(e)
+        except BaseException as exc:
+            self.future.set_exception(exc)
+            # Break a reference cycle with the exception 'exc'
+            self = None
         else:
             self.future.set_result(result)
 
diff --git a/Misc/NEWS.d/next/Library/2017-08-22-12-44-48.bpo-31249.STPbb9.rst b/Misc/NEWS.d/next/Library/2017-08-22-12-44-48.bpo-31249.STPbb9.rst
@@ -0,0 +1,2 @@
+concurrent.futures: WorkItem.run() used by ThreadPoolExecutor now breaks a
+reference cycle between an exception object and the WorkItem object.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+concurrent.futures: WorkItem.run() used by ThreadPoolExecutor now breaks a`
	`2`	`+reference cycle between an exception object and the WorkItem object.`