https://github.com/python/cpython/commit/5a1ecc8cc7d3dfedd14adea1c3cdc3cfeb79f0e1
commit: 5a1ecc8cc7d3dfedd14adea1c3cdc3cfeb79f0e1
branch: main
author: Fabio Zadrozny <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2024-01-23T14:12:50+02:00
summary:
gh-114423: Remove DummyThread from threading._active when thread dies
(GH-114424)
files:
A Misc/NEWS.d/next/Library/2024-01-22-11-43-38.gh-issue-114423.6mMoPH.rst
M Lib/test/test_threading.py
M Lib/threading.py
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 7160c53d691ba2..dbdc46fff1e313 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -227,8 +227,6 @@ def f():
tid = _thread.start_new_thread(f, ())
done.wait()
self.assertEqual(ident[0], tid)
- # Kill the "immortal" _DummyThread
- del threading._active[ident[0]]
# run with a small(ish) thread stack size (256 KiB)
def test_various_ops_small_stack(self):
@@ -256,11 +254,29 @@ def test_various_ops_large_stack(self):
def test_foreign_thread(self):
# Check that a "foreign" thread can use the threading module.
+ dummy_thread = None
+ error = None
def f(mutex):
- # Calling current_thread() forces an entry for the foreign
- # thread to get made in the threading._active map.
- threading.current_thread()
- mutex.release()
+ try:
+ nonlocal dummy_thread
+ nonlocal error
+ # Calling current_thread() forces an entry for the foreign
+ # thread to get made in the threading._active map.
+ dummy_thread = threading.current_thread()
+ tid = dummy_thread.ident
+ self.assertIn(tid, threading._active)
+ self.assertIsInstance(dummy_thread, threading._DummyThread)
+ self.assertIs(threading._active.get(tid), dummy_thread)
+ # gh-29376
+ self.assertTrue(
+ dummy_thread.is_alive(),
+ 'Expected _DummyThread to be considered alive.'
+ )
+ self.assertIn('_DummyThread', repr(dummy_thread))
+ except BaseException as e:
+ error = e
+ finally:
+ mutex.release()
mutex = threading.Lock()
mutex.acquire()
@@ -268,20 +284,25 @@ def f(mutex):
tid = _thread.start_new_thread(f, (mutex,))
# Wait for the thread to finish.
mutex.acquire()
- self.assertIn(tid, threading._active)
- self.assertIsInstance(threading._active[tid], threading._DummyThread)
- #Issue 29376
- self.assertTrue(threading._active[tid].is_alive())
- self.assertRegex(repr(threading._active[tid]), '_DummyThread')
-
+ if error is not None:
+ raise error
+ self.assertEqual(tid, dummy_thread.ident)
# Issue gh-106236:
with self.assertRaises(RuntimeError):
- threading._active[tid].join()
- threading._active[tid]._started.clear()
+ dummy_thread.join()
+ dummy_thread._started.clear()
with self.assertRaises(RuntimeError):
- threading._active[tid].is_alive()
-
- del threading._active[tid]
+ dummy_thread.is_alive()
+ # Busy wait for the following condition: after the thread dies, the
+ # related dummy thread must be removed from threading._active.
+ timeout = 5
+ timeout_at = time.monotonic() + timeout
+ while time.monotonic() < timeout_at:
+ if threading._active.get(dummy_thread.ident) is not dummy_thread:
+ break
+ time.sleep(.1)
+ else:
+ self.fail('It was expected that the created threading._DummyThread
was removed from threading._active.')
# PyThreadState_SetAsyncExc() is a CPython-only gimmick, not (currently)
# exposed at the Python level. This test relies on ctypes to get at it.
diff --git a/Lib/threading.py b/Lib/threading.py
index c561800a128059..ecf799bc26ab06 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -54,6 +54,13 @@
TIMEOUT_MAX = _thread.TIMEOUT_MAX
del _thread
+# get thread-local implementation, either from the thread
+# module, or from the python fallback
+
+try:
+ from _thread import _local as local
+except ImportError:
+ from _threading_local import local
# Support for profile and trace hooks
@@ -1476,10 +1483,36 @@ def __init__(self):
_active[self._ident] = self
+# Helper thread-local instance to detect when a _DummyThread
+# is collected. Not a part of the public API.
+_thread_local_info = local()
+
+
+class _DeleteDummyThreadOnDel:
+ '''
+ Helper class to remove a dummy thread from threading._active on __del__.
+ '''
+
+ def __init__(self, dummy_thread):
+ self._dummy_thread = dummy_thread
+ self._tident = dummy_thread.ident
+ # Put the thread on a thread local variable so that when
+ # the related thread finishes this instance is collected.
+ #
+ # Note: no other references to this instance may be created.
+ # If any client code creates a reference to this instance,
+ # the related _DummyThread will be kept forever!
+ _thread_local_info._track_dummy_thread_ref = self
+
+ def __del__(self):
+ with _active_limbo_lock:
+ if _active.get(self._tident) is self._dummy_thread:
+ _active.pop(self._tident, None)
+
+
# Dummy thread class to represent threads not started here.
-# These aren't garbage collected when they die, nor can they be waited for.
-# If they invoke anything in threading.py that calls current_thread(), they
-# leave an entry in the _active dict forever after.
+# These should be added to `_active` and removed automatically
+# when they die, although they can't be waited for.
# Their purpose is to return *something* from current_thread().
# They are marked as daemon threads so we won't wait for them
# when we exit (conform previous semantics).
@@ -1495,6 +1528,7 @@ def __init__(self):
self._set_native_id()
with _active_limbo_lock:
_active[self._ident] = self
+ _DeleteDummyThreadOnDel(self)
def _stop(self):
pass
@@ -1676,14 +1710,6 @@ def main_thread():
# XXX Figure this out for subinterpreters. (See gh-75698.)
return _main_thread
-# get thread-local implementation, either from the thread
-# module, or from the python fallback
-
-try:
- from _thread import _local as local
-except ImportError:
- from _threading_local import local
-
def _after_fork():
"""
diff --git
a/Misc/NEWS.d/next/Library/2024-01-22-11-43-38.gh-issue-114423.6mMoPH.rst
b/Misc/NEWS.d/next/Library/2024-01-22-11-43-38.gh-issue-114423.6mMoPH.rst
new file mode 100644
index 00000000000000..7b77b73295d948
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-01-22-11-43-38.gh-issue-114423.6mMoPH.rst
@@ -0,0 +1 @@
+``_DummyThread`` entries in ``threading._active`` are now automatically
removed when the related thread dies.
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