bpo-36607: Eliminate RuntimeError raised by asyncio.all_tasks() (GH-13971)

If internal tasks weak set is changed by another thread during iteration. https://bugs.python.org/issue36607 (cherry picked from commit 65aa64f) Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>

Author: miss-islington

Lib/asyncio/tasks.py

@@ -35,9 +35,22 @@ def all_tasks(loop=None):
  """Return a set of all tasks for the loop."""
  if loop is None:
  loop = events.get_running_loop()
- # NB: set(_all_tasks) is required to protect
- # from https://bugs.python.org/issue34970 bug
- return {t for t in list(_all_tasks)
+ # Looping over a WeakSet (_all_tasks) isn't safe as it can be updated from another
+ # thread while we do so. Therefore we cast it to list prior to filtering. The list
+ # cast itself requires iteration, so we repeat it several times ignoring
+ # RuntimeErrors (which are not very likely to occur). See issues 34970 and 36607 for
+ # details.
+ i = 0
+ while True:
+ try:
+ tasks = list(_all_tasks)
+ except RuntimeError:
+ i += 1
+ if i >= 1000:
+ raise
+ else:
+ break
+ return {t for t in tasks
  if futures._get_loop(t) is loop and not t.done()}
 
 
@@ -47,9 +60,22 @@ def _all_tasks_compat(loop=None):
  # method.
  if loop is None:
  loop = events.get_event_loop()
- # NB: set(_all_tasks) is required to protect
- # from https://bugs.python.org/issue34970 bug
- return {t for t in list(_all_tasks) if futures._get_loop(t) is loop}
+ # Looping over a WeakSet (_all_tasks) isn't safe as it can be updated from another
+ # thread while we do so. Therefore we cast it to list prior to filtering. The list
+ # cast itself requires iteration, so we repeat it several times ignoring
+ # RuntimeErrors (which are not very likely to occur). See issues 34970 and 36607 for
+ # details.
+ i = 0
+ while True:
+ try:
+ tasks = list(_all_tasks)
+ except RuntimeError:
+ i += 1
+ if i >= 1000:
+ raise
+ else:
+ break
+ return {t for t in tasks if futures._get_loop(t) is loop}
 
 
 class Task(futures._PyFuture): # Inherit Python Task implementation

Misc/NEWS.d/next/Library/2019-06-11-13-52-04.bpo-36607.5_mJkQ.rst

@@ -0,0 +1,2 @@
+Eliminate :exc:`RuntimeError` raised by :func:`asyncio.all_tasks()` if
+internal tasks weak set is changed by another thread during iteration.