ninja-build/ninja

linux: `pool = console` does not forward signals (e.g. SIGTERM) to the console process

Open

#2116 opened on Apr 2, 2022

View on GitHub
 (2 comments) (0 reactions) (0 assignees)C++ (10,194 stars) (1,544 forks)batch import
bughelp wanted

Description

If I have a simple build.ninja:

rule sleep
  command = $
    echo hi $
    && sleep 100

build sleep : sleep
  pool = console

And I run ninja sleep, I get a process tree like this:

sh (PID: 1)
└─ ninja sleep (PID: 2)
   └─ sleep 100 (PID: 3)

If I now send a SIGTERM to ninja (kill 2), I’d expect that signal to be forwarded to sleep. However, ninja will swallow the signal and nothing happens. The same happens with e.g. SIGINT.

If I remove pool = console, the SIGTERM is forwarded correctly (this was fixed in https://github.com/ninja-build/ninja/pull/743) cc @nicolasdespres

Forwarding signals is quite important if I want to run ninja processes inside a service manager. For example if I want to run ninja sleep (or any program executable I build) inside of s6, s6-supervise will send SIGTERM (or any other signal) to ninja sleep, expecting it to stop running.

Contributor guide

Tech stack
cpp
Domain
build system
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++signal handlingprocess management
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
55
Research direction
Investigate the signal forwarding mechanism in ninja's source code, specifically in `src/subprocess.cc` or related files. The issue notes that without `pool = console`, signals are forwarded correctly (fixed in PR #743). For the console pool, find where the process group is set or where signal handlers are configured. Compare the console pool implementation with the default pool to identify the missing signal forwarding. Look at how `SIGTERM` and `SIGINT` are handled in the subprocess code. Consider adding appropriate signal forwarding for console pool processes.