[Python-checkins] bpo-46787: Fix `ProcessPoolExecutor exception` memory leak (GH-31408) (#31408)

[JelleZijlstra]

https://github.com/python/cpython/commit/9c204b148fad9742ed19b3bce173073cdec79819
commit: 9c204b148fad9742ed19b3bce173073cdec79819
branch: main
author: themylogin <themylogin at gmail.com>
committer: JelleZijlstra <jelle.zijlstra at gmail.com>
date: 2022-05-02T14:24:39-06:00
summary:

bpo-46787: Fix `ProcessPoolExecutor exception` memory leak (GH-31408) (#31408)

Do not store `ProcessPoolExecutor` work item exception traceback that prevents
exception frame locals from being garbage collected.

files:
A Misc/NEWS.d/next/Library/2022-02-18-20-09-29.bpo-46787.juwWc0.rst
M Lib/concurrent/futures/process.py

diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
index 695f7733305ed..0d49379c9bf7c 100644
--- a/Lib/concurrent/futures/process.py
+++ b/Lib/concurrent/futures/process.py
@@ -125,6 +125,9 @@ class _ExceptionWithTraceback:
     def __init__(self, exc, tb):
         tb = ''.join(format_exception(type(exc), exc, tb))
         self.exc = exc
+        # Traceback object needs to be garbage-collected as its frames
+        # contain references to all the objects in the exception scope
+        self.exc.__traceback__ = None
         self.tb = '\n"""\n%s"""' % tb
     def __reduce__(self):
         return _rebuild_exc, (self.exc, self.tb)
diff --git a/Misc/NEWS.d/next/Library/2022-02-18-20-09-29.bpo-46787.juwWc0.rst b/Misc/NEWS.d/next/Library/2022-02-18-20-09-29.bpo-46787.juwWc0.rst
new file mode 100644
index 0000000000000..cf167ff48115b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-02-18-20-09-29.bpo-46787.juwWc0.rst
@@ -0,0 +1 @@
+Fix :class:`concurrent.futures.ProcessPoolExecutor` exception memory leak