Increase the open file soft limit to the hard limit

[edolstra]

Motivation

On some platforms (macOS), the default soft limit is very low, but the hard limit is high. So let's just raise it the maximum permitted.

Context

Summary by CodeRabbit

• Chores
  • Improved system-level file descriptor handling on non-Windows platforms to raise the soft limit up to the hard limit where possible.
  • Applied automatically during application initialization as a best-effort step; failures are ignored to avoid impacting startup.
  • Aims to support higher concurrent file operations without changing existing initialization behavior.

[coderabbitai]

📝 Walkthrough

Walkthrough

A new non-Windows-only function bumpFileLimit() was added to raise the process soft limit for open file descriptors (RLIMIT_NOFILE) up to the hard limit using getrlimit/setrlimit; it is called at the end of initNix(bool loadConfig) during initialization. (46 words)

Changes

Cohort / File(s)	Summary
File Descriptor Limit Configuration src/libmain/shared.cc	Added bumpFileLimit() (non-Windows) which reads RLIMIT_NOFILE via getrlimit and, if needed, sets the soft limit to the hard limit with setrlimit (errors ignored). Invoked at end of initNix(bool loadConfig). Also added #include <sys/resource.h> guarded by platform.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 I nudged the limits, soft to hard,

More files to open, working hard.
A tiny bump, a sysadmin's cheer,
Nix wakes up with room to steer.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Increase the open file soft limit to the hard limit' directly and specifically describes the main change made in the pull request, which adds a bumpFileLimit() function to increase the soft limit for open files (RLIMIT_NOFILE) to the hard limit.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch bump-file-limit

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No actionable comments were generated in the recent review. 🎉

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/libmain/shared.cc`:
- Around line 119-137: The build breaks on some platforms because
bumpFileLimit() uses struct rlimit and the getrlimit/setrlimit functions without
directly including the header that declares them; add a platform-guarded include
of <sys/resource.h> at the top of the file (guarded by `#ifndef` _WIN32 if needed)
so that struct rlimit, getrlimit, and setrlimit are declared where
bumpFileLimit() is defined.

[github-actions]

🚀 Deployed on https://698ceac0b1b376af404020cd--determinate-nix.netlify.app

[edolstra]

Upstream NixOS#15205.