Remove thread join from threadexception plugin (#13027)

As per review comment: #13016 (comment).

Closes #13028.

---------

Co-authored-by: Bruno Oliveira <[email protected]>

Author: graingert

changelog/13016.improvement.rst

@@ -1,7 +1,6 @@
 A number of :ref:`threadexception <unraisable>` enhancements:
 
 * Set the excepthook as early as possible and unset it as late as possible, to collect the most possible number of unhandled exceptions from threads.
-* join threads for 1 second just before unsetting the excepthook, to collect any straggling exceptions
 * Collect multiple thread exceptions per test phase.
 * Report the :mod:`tracemalloc` allocation traceback (if available).
 * Avoid using a generator based hook to allow handling :class:`StopIteration` in test failures.

src/_pytest/threadexception.py

@@ -5,7 +5,6 @@
 import functools
 import sys
 import threading
-import time
 import traceback
 from typing import NamedTuple
 from typing import TYPE_CHECKING
@@ -25,22 +24,6 @@
     from exceptiongroup import ExceptionGroup
 
 
-def join_threads() -> None:
-    start = time.monotonic()
-    current_thread = threading.current_thread()
-    # This function is executed right at the end of the pytest run, just
-    # before we return an exit code, which is where the interpreter joins
-    # any remaining non-daemonic threads anyway, so it's ok to join all the
-    # threads. However there might be threads that depend on some shutdown
-    # signal that happens after pytest finishes, so we want to limit the
-    # join time somewhat. A one second timeout seems reasonable.
-    timeout = 1
-    for thread in threading.enumerate():
-        if thread is not current_thread and not thread.daemon:
-            # TODO: raise an error/warning if there's dangling threads.
-            thread.join(timeout - (time.monotonic() - start))
-
-
 class ThreadExceptionMeta(NamedTuple):
     msg: str
     cause_msg: str
@@ -96,7 +79,9 @@ def cleanup(
 ) -> None:
     try:
         try:
-            join_threads()
+            # We don't join threads here, so exceptions raised from any
+            # threads still running by the time _threading_atexits joins them
+            # do not get captured (see #13027).
             collect_thread_exception(config)
         finally:
             threading.excepthook = prev_hook

testing/test_threadexception.py

@@ -195,17 +195,16 @@ def test_2(): pass
 def test_unhandled_thread_exception_after_teardown(pytester: Pytester) -> None:
     pytester.makepyfile(
         test_it="""
-        import time
         import threading
         import pytest
 
         def thread():
             def oops():
-                time.sleep(0.5)
                 raise ValueError("Oops")
 
             t = threading.Thread(target=oops, name="MyThread")
             t.start()
+            t.join()
 
         def test_it(request):
             request.config.add_cleanup(thread)