BUG: numpy.lib.recfunctions.structured_to_unstructured is not thread-safe #21320
Description
Describe the issue:
numpy.lib.recfunctions.structured_to_unstructured uses numpy.testing.suppress_warnings, which is inherently thread unsafe. However, structured_to_unstructured is not documented as thread unsafe, and would otherwise not be expected to alter global state.
If this function is used in a multi-threaded program, multiple suppress_warnings context managers may be entered and exited out of order, leaving the global warnings.show_warnings handler in an invalid state. Any subsequent code that issues any warning will trigger an AttributeError instead. This issue resulted in a crash of one of our production services. This error is related to #8413, and an example of this failure is constructed below.
From a quick search, this usage in structured_to_unstructured appears to be the only usage of suppress_warnings in the numpy library outside of testing routines. It would seem this suppress_warnings context manager is only suitable for testing purposes, and should not be used in library or production code.
Reproduce the code example:
import logging
import warnings
import threading
from numpy.testing import suppress_warnings
def thread_a():
logging.info("Entering a")
with suppress_warnings() as sup:
logging.info("Entered a")
entered_a.set()
entered_b.wait()
logging.info("Exiting a")
logging.info("Exited a")
exited_a.set()
def thread_b():
logging.info("Entering b")
entered_a.wait()
with suppress_warnings() as sup:
logging.info("Entered b")
entered_b.set()
exited_a.wait()
logging.info("Exiting b")
logging.info("Exited b")
exited_b.set()
entered_a = threading.Event()
exited_a = threading.Event()
entered_b = threading.Event()
exited_b = threading.Event()
thread1 = threading.Thread(target=thread_a)
thread2 = threading.Thread(target=thread_b)
entered_a.clear()
exited_a.clear()
entered_b.clear()
exited_b.clear()
thread1.start()
thread2.start()
exited_b.wait()
warnings.warn('test')Error message:
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
Input In [11], in <cell line: 14>()
10 thread2.start()
12 exited_b.wait()
---> 14 warnings.warn('test')
File /usr/lib/python3.10/warnings.py:109, in _showwarnmsg(msg)
105 if not callable(sw):
106 raise TypeError("warnings.showwarning() must be set to a "
107 "function or method")
--> 109 sw(msg.message, msg.category, msg.filename, msg.lineno,
110 msg.file, msg.line)
111 return
112 _showwarnmsg_impl(msg)
File /usr/lib/python3.10/site-packages/numpy/testing/_private/utils.py:2273, in suppress_warnings._showwarning(self, message, category, filename, lineno, use_warnmsg, *args, **kwargs)
2271 if self._forwarding_rule == "always":
2272 if use_warnmsg is None:
-> 2273 self._orig_show(message, category, filename, lineno,
2274 *args, **kwargs)
2275 else:
2276 self._orig_showmsg(use_warnmsg)
AttributeError: 'suppress_warnings' object has no attribute '_orig_show'NumPy/Python version information:
1.22.3 3.10.4 (main, Mar 23 2022, 23:05:40) [GCC 11.2.0]