[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

STINNER Victor  added the comment:

Cool, my threading change works as expected! The name of the target function 
was logged in bpo-41739 issue.

https://buildbot.python.org/all/#/builders/509/builds/172

0:00:28 load avg: 3.58 [ 36/424/1] test_logging failed (env changed)
Warning -- threading_cleanup() failed to cleanup 2 threads (count: 2, dangling: 
3)
Warning -- Dangling thread: 
Warning -- Dangling thread: 
Warning -- Dangling thread: <_MainThread(MainThread, started 4396920310576)>

See "": the two 
leaked threads are running the removeTarget() function which come from 
MemoryHandlerTest.test_race_between_set_target_and_flush().

By the way, Serhiy was right about the name of having an unique repr() even if 
the target is the same, since it's the case here ;-) Well "4396862667024" is 
different than "4396595259664", but it's more convinient to have short numbers 
like "Thread-4" and "Thread-11".

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

STINNER Victor  added the comment:

I merged my change with "Thread-1 (func)" format: add the target name, but keep 
"Thread-3" to distinguish two different threads with the same target name.

--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 98c16c991d6e70a48f4280a7cd464d807bdd9f2b by Victor Stinner in 
branch 'master':
bpo-41833: threading.Thread now uses the target name (GH-22357)
https://github.com/python/cpython/commit/98c16c991d6e70a48f4280a7cd464d807bdd9f2b


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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

STINNER Victor  added the comment:

> Ideally, I would prefer separate counters for different names

IMO if you want to go at the level of details, I suggest you to generate 
yourself thread names:

threads = [threading.Thread(name=f"MyThread-{i}") for i in range(1, 6)]

Maintaining a list of thread names sounds overkill to me. It would be quite 
complicated and would increase the memory footprint, for little benefit.

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Ideally, I would prefer separate counters for different names, and omitting a 
number for the first thread with unique name:

  doit
  doit-2
  Thread-1
  Thread-2
  print
  print-2
  doit-3

But it is not feasible. It would require supporting a cache which can grow with 
every new thread and non-trivial code to avoid race conditions. So I am fine 
with Ammar's idea.

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

STINNER Victor  added the comment:

I rewrote my PR to generate names like "Thread-3 (func)", rather than just 
"func". So if two target functions have the same name, or if two threads use 
the same target, it remains possible to distinguish the two threads.

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[Ammar Askar]

Ammar Askar  added the comment:

Having the target in the thread name definitely seems like a good idea and 
would help ease debugging, not just for our tests but when printing thread 
objects in general. 

I would agree with the suggestion of placing the counter in there for when 
multiple threads get spawned with the same target or maybe even using names 
like:

  Thread-1 (doit)
  Thread-2
  Thread-3 (print)

might be better just for people who are familiar with them.

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nosy: +ammar2

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

STINNER Victor  added the comment:

See also bpo-15500 "Python should support exporting thread names to the OS".

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

STINNER Victor  added the comment:

> And what if run different threads with the same target or with different 
> targets with the same name?

If multiple Thread objects using the same target (or different targets with the 
same name), they all get the same name using my PR 22357.

> Would not "Thread-3" be more useful in this case?

Well, that's an open question. In my experience, "Thread" name is pretty 
useless.

What if I modify my PR to add "-{counter}" (ex: "func-3" for 
target.__name__="func") to the default name? Reuse _counter().

Pseudo-code:

self._name = str(name)
try:
base_name = target.__name__
except AttributeError:
base_name = "Thread"
if not self._name:
self._name = "{base_name)-{_counter()}"

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

And what if run different threads with the same target or with different 
targets with the same name? Would not "Thread-3" be more useful in this case?

for i in range(10):
Thread(target=print, args=(i,)).start()

for i in range(10):
def doit(i=i):
print(i)
Thread(target=doit).start()

--
nosy: +serhiy.storchaka

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

Change by STINNER Victor :


--
keywords: +patch
pull_requests: +21395
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/22357

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[issue41833] threading.Thread: use target name if the name parameter is omitted

[STINNER Victor]

New submission from STINNER Victor :

When debugging race conditions in a multithreaded application with many 
threads, it's hard to debug when threads have generic names like "Thread-3".

I propose to use the target name in threading.Thread constructor if the name 
parameter is omitted.


See for example bpo-41739 with "Dangling thread: ": the "Thread-3" name is not helpful. I suspect that the 
bug comes from threading.Thread(target=remove_loop, args=(fn, del_count)): with 
my proposed change, the thread would be called "target=remove_loop", which is 
more helpful than "Thread".

Fall back on _newname() as usual if target.__name__ attribute does not exist.

Attached PR implements this idea.

--
components: Library (Lib)
messages: 377314
nosy: vstinner
priority: normal
severity: normal
status: open
title: threading.Thread: use target name if the name parameter is omitted
versions: Python 3.10

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