Module: Tailwindcss::ProcessRunner

Defined in:
lib/tailwindcss/process_runner.rb

Overview

Runs a child process and forwards stop signals (INT/TERM) to it, blocking until it exits, so a process manager that signals this process directly (e.g. foreman) doesn’t leave the child orphaned. Shaped like Process.spawn/+Kernel#system+: it takes an env hash followed by the command.

Constant Summary collapse

FORWARDED_SIGNALS =

Signals we forward to the spawned process so it shuts down with us instead of being orphaned.

%w[INT TERM].freeze

Class Method Summary collapse

Class Method Details

.spawn_and_wait(env, *command) ⇒ Object

Spawn command with env and block until it exits, forwarding INT (Ctrl-C) and TERM (e.g. foreman shutdown) to it so a process manager that signals us directly doesn’t leave an orphaned child behind. Restores the previous signal handlers before returning so the process-global traps aren’t left changed. Returns the name of the signal that was received (e.g. “TERM”), or nil if the child exited on its own.



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# File 'lib/tailwindcss/process_runner.rb', line 19

def spawn_and_wait(env, *command)
  pid = nil
  received_signal = nil
  previous_traps = {}

  forward_signal = ->(signal) do
    if pid
      Process.kill(signal, pid)
    end
  rescue Errno::ESRCH
    # the child already exited
  end

  # Trap immediately before spawning. If a signal lands before pid is
  # assigned, remember it and forward it once the child exists.
  FORWARDED_SIGNALS.each do |signal|
    previous_traps[signal] = trap(signal) do
      received_signal ||= signal
      forward_signal.call(signal)
    end
  end

  pid = Process.spawn(env, *command)
  # If a signal arrived during spawn (before pid was set), the handler
  # couldn't forward it yet, so forward it now.
  if received_signal
    forward_signal.call(received_signal)
  end
  Process.wait(pid)
  # Drop the pid so a late signal can't kill a process that reused it.
  pid = nil

  received_signal
ensure
  previous_traps.each do |signal, previous_trap|
    trap(signal, previous_trap)
  end
end