On Wed, Sep 12, 2018 at 06:59:44AM -0700, Ethan Furman wrote: > On 09/12/2018 05:17 AM, Steven D'Aprano wrote: [...] > >We could solve this race condition with locking, or by making the pair > >of steps:
[...] > >I'm not an expert on threaded code, so it is possible I've missed some > >non-obvious fix for this, but I expect not. In general, solving race > >conditions without deadlocks is a hard problem. > > I believe the solution is `threading.local()`, and Python would > automatically use it in these situations. I'm finding it hard to understand the documentation for threading.local(): https://docs.python.org/3/library/threading.html#threading.local as there isn't any *wink* although it does refer to the docstring of a private implementation module. But I can't get it to work. Perhaps I'm doing something wrong: import time from threading import Thread, local def func(): pass def attach(value): func.__params__ = local() func.__params__.value = value def worker(i): print("called from thread %s" % i) attach(i) assert func.__params__.value == i time.sleep(3) value = func.__params__.value if value != i: print("mismatch", i, value) for i in range(5): t = Thread(target=worker, args=(i,)) t.start() print() When I run that, each of the threads print their "called from ..." message, the assertions all pass, then a couple of seconds later they consistently all raise exceptions: Exception in thread Thread-1: Traceback (most recent call last): File "/usr/local/lib/python3.5/threading.py", line 914, in _bootstrap_inner self.run() File "/usr/local/lib/python3.5/threading.py", line 862, in run self._target(*self._args, **self._kwargs) File "<stdin>", line 5, in worker AttributeError: '_thread._local' object has no attribute 'value' In any case, if Steve Barnes didn't actually intend for the __params__ to be attached to the function object as an externally visible attribute, the whole point is moot. -- Steve _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
