Use os.closerange instead of counting to 1 billion

[phihag]

In billiard.compat.close_open_fds, after checking whether os.closerange exists, if it exists we did not use it, which makes no sense at all.

Instead, the implementation called os.close, os.sysconf("SC_OPENMAX") - len(keep) times.

On most systems, SC_OPENMAX is something like 1024, 4096, or 65536.
In the latter case, calling it will already take 30ms on my system, almost noticable for humans.

But docker (and some systems) uses a really high value:

docker run --rm python python -c 'import os;print(os.sysconf("SC_OPEN_MAX"))'
1073741816

In other words, when running in docker we were counting to 1 billlion, at 2 million per second.
The single function call close_open_fd([0,1,2]) takes almost 10 minutes there!

The fix is trivial: When os.closerange is available, use the existing implementation. It's right there!

An alternative approach would be to just list all open handles with psutil.Process().open_files() or so, and then just close those few.

[auvipy]

can you please add unit tests to verify this? and there is no regression?

[Copilot]

Pull Request Overview

This PR simplifies close_open_fds by removing the manual per-FD fallback loop and always using the existing closerange helper, improving performance especially on systems with very high SC_OPEN_MAX.

• Always invoke closerange to close descriptor ranges instead of iterating each FD
• Removed the else block that manually closed each FD in reverse
• No functional changes to get_errno

Comments suppressed due to low confidence (4)

billiard/compat.py:130

• The custom closerange implementation still iterates over each file descriptor. To leverage the optimized system call when available, consider aliasing closerange = os.closerange if os.closerange exists or calling os.closerange directly.

def closerange(fd_low, fd_high):  # noqa

billiard/compat.py:141

• [nitpick] The variable names kL and kH are not descriptive. Consider renaming them to something like lower_bounds and upper_bounds (or starts and ends) to clarify their purpose.

for low, high in zip_longest(kL, kH):

billiard/compat.py:134

• [nitpick] Add a docstring for close_open_fds to describe its behavior, parameters (keep list), and side effects, improving maintainability.

def close_open_fds(keep=None):

billiard/compat.py:134

• Include unit tests to verify that close_open_fds correctly closes ranges via closerange for very large FD limits and respects the keep list.

def close_open_fds(keep=None):