Give the Puma plugin the pid of the litestream process

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## [Unreleased]
 
+- The Puma plugin holds the pid of the litestream process itself, so stopping Puma stops replication instead of leaving the daemon running.
+
 ## [0.14.0] - 2025-06-14
 
 - Change async behaviour of replicate and other commands ([@hschne](https://github.com/fractaledmind/litestream-ruby/pull/62))

lib/litestream/commands.rb

@@ -94,9 +94,9 @@ def executable(exe_path: DEFAULT_DIR)
         exe_file
       end
 
-      # Replicate can be run either as a fork or in the same process, depending on the context.
-      # Puma will start replication as a forked process, while running replication from a rake
-      # tasks won't.
+      # Replicate runs either as a child process or in the foreground, depending on the context.
+      # The Puma plugin starts it as a child and gets its pid back; the rake task runs it in the
+      # foreground and streams its output.
       def replicate(async: false, **argv)
         cmd = prepare("replicate", argv)
         run_replicate(cmd, async: async)
@@ -169,9 +169,13 @@ def run(cmd, tabled_output:)
         rows.map { keys.zip(_1).to_h }
       end
 
+      # Async replication returns the pid of the litestream process itself so a
+      # supervisor can signal and wait on it. Forking a Ruby child that then
+      # execs would hand back a pid that exits (as a zombie) while the daemon
+      # is reparented to init and outlives its supervisor.
       def run_replicate(cmd, async:)
         if async
-          exec(*cmd) if fork.nil?
+          Process.spawn(*cmd)
         else
           # When running in-process, we capture output continuously and write to stdout.
           IO.popen(cmd, err: [:child, :out]) do |io|

lib/puma/plugin/litestream.rb

@@ -2,17 +2,13 @@
 
 # Copied from https://github.com/rails/solid_queue/blob/15408647f1780033dad223d3198761ea2e1e983e/lib/puma/plugin/solid_queue.rb
 Puma::Plugin.create do
-  attr_reader :puma_pid, :litestream_pid, :log_writer
+  attr_reader :litestream_pid, :log_writer
 
   def start(launcher)
     @log_writer = launcher.log_writer
-    @puma_pid = $$
 
     launcher.events.on_booted do
-      @litestream_pid = fork do
-        Thread.new { monitor_puma }
-        Litestream::Commands.replicate(async: true)
-      end
+      @litestream_pid = Litestream::Commands.replicate(async: true)
 
       in_background do
         monitor_litestream
@@ -33,10 +29,6 @@ def stop_litestream
   rescue Errno::ECHILD, Errno::ESRCH
   end
 
-  def monitor_puma
-    monitor(:puma_dead?, "Detected Puma has gone away, stopping Litestream...")
-  end
-
   def monitor_litestream
     monitor(:litestream_dead?, "Detected Litestream has gone away, stopping Puma...")
   end
@@ -59,10 +51,6 @@ def litestream_dead?
     true
   end
 
-  def puma_dead?
-    Process.ppid != puma_pid
-  end
-
   def log(...)
     log_writer.log(...)
   end

test/litestream/test_commands.rb

@@ -873,3 +873,29 @@ def test_output_formatting_generates_formatted_table
     end
   end
 end
+
+class TestReplicateProcess < ActiveSupport::TestCase
+  def test_async_replicate_returns_the_pid_of_the_litestream_process
+    Dir.mktmpdir do |dir|
+      executable = File.join(dir, "litestream")
+      pid_file = File.join(dir, "pid")
+      # Exits cleanly on INT like the real daemon, so Process.wait leaves a
+      # normal exit status behind for tests that read $? after a stubbed command.
+      File.write(executable, "#!/bin/sh\ntrap 'exit 0' INT TERM\necho $$ > #{pid_file}\nwhile :; do sleep 1; done\n")
+      File.chmod(0o755, executable)
+
+      Litestream::Commands.stub :executable, executable do
+        pid = Litestream::Commands.replicate(async: true)
+        sleep 0.2 until File.exist?(pid_file) && !File.read(pid_file).strip.empty?
+
+        assert_equal File.read(pid_file).to_i, pid
+      ensure
+        if pid
+          Process.kill(:INT, pid)
+          Process.wait(pid)
+          assert_raises(Errno::ECHILD) { Process.wait(pid, Process::WNOHANG) }
+        end
+      end
+    end
+  end
+end