lake sometimes hangs on NetBSD

Prerequisites

• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

After packaging lean 4.32.1, I've been building it repeatedly in a clean environment. Sometimes (1 out of 3? 5? times) during a build, lake will hang.

I've attached a debugger once, reading the backtrace there is a process hanging in pthread_join, one in fread, the others are idle in pthread_cond_timedwait.

I can only see one fread() in the code, in src/runtime/io.cpp - perhaps this code should have a timeout (i.e. use select or poll and non-blocking reads.

Context

n/a

Steps to Reproduce

1. Build lean4 4.32.1 repeatedly.
2. be unlucky

Expected behavior: [Clear and concise description of what you expect to happen]

lake should not hang.

Actual behavior: [Clear and concise description of what actually happens]

lake sometimes does hang.

Versions

4.32.1
NetBSD 11.99.7/x86_64

Additional Information

n/a

Impact

Start with src/runtime/io.cpp and the reported backtraces involving fread, pthread_join, and pthread_cond_timedwait. Repeatedly build Lean 4.32.1 on NetBSD 11.99.7 to investigate the intermittent hang; done means lake completes without hanging during repeated clean builds.