New submission from Gregory P. Smith <g...@krypto.org>:
It'd be handy to have a function to determine if there are multiple threads in
the current process or not - at least on POSIXish systems. This would be
useful anytime a library is trying to use os.fork(), as fork() is not safe in a
multi-threaded process.
Motivation: I want to _use_ this API to consider raising RuntimeWarnings in
libraries that call fork() to highlight the problem to people attempting to use
that code in multithreaded processes.
As POSIXy OSes don't usually have a simple API to get this information, one
implementation such as this could make sense:
```
def is_process_multithreaded() -> bool:
"""Are there multiple threads in this process? OSError if no such OS API is
available."""
threads = 0
ourself = str(os.gettid())
i_feel_seen = False
try:
# Linux, NetBSD, any others?
with os.scandir('/proc/self/task') as tasks:
for task_dir_entry in tasks:
# tid named subdirs should be the only thing that exists.
# We do a simple conformity check just in case.
if task_dir_entry.name.isdigit():
if task_dir_entry.name == ourself:
i_feel_seen = True
threads += 1
if i_feel_seen and threads > 1:
return True # Multiple threads confirmed.
except EnvironmentError:
raise OSError('Unable to count threads on this platform.')
if i_feel_seen and threads == 1:
return False
else:
raise OSError(f'Unclear. Found {threads} in /proc/self/task and did not
find ourself.')
```
macOS has mach darwin kernel APIs that can do this. Not well documented but
they do work -
https://stackoverflow.com/questions/21478229/how-to-count-number-of-alive-threads-in-ios
FreeBSD has APIs that can do this (see FreeBSD usr.bin/procstat/ source).
configure.ac checks and an extension module would be needed to integrate those.
My use case is not relevant to Windows (a platform unburdened by fork) but
Windows APIs to answer the question exist if anyone has a reason to want this
there as well -
https://stackoverflow.com/questions/3749668/how-to-query-the-thread-count-of-a-process-using-the-regular-windows-c-c-apis
----------
components: Library (Lib)
messages: 411420
nosy: gregory.p.smith
priority: normal
severity: normal
stage: needs patch
status: open
title: Add an API to indicate if the process might have multiple threads
type: enhancement
versions: Python 3.11
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue46493>
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