Add a Puma plugin for Solid Queue

lib/puma/plugin/solid_queue.rb

@@ -0,0 +1,63 @@
+require "puma/plugin"
+
+Puma::Plugin.create do
+  attr_reader :puma_pid, :solid_queue_pid, :log_writer
+
+  def start(launcher)
+    @log_writer = launcher.log_writer
+    @puma_pid = $$
+    @solid_queue_pid = fork do
+      Thread.new { monitor_puma }
+      SolidQueue::Supervisor.start(mode: :all)
+    end
+
+    launcher.events.on_stopped { stop_solid_queue }
+
+    in_background do
+      monitor_solid_queue
+    end
+  end
+
+  private
+    def stop_solid_queue
+      Process.waitpid(solid_queue_pid, Process::WNOHANG)
+      log "Stopping Solid Queue..."
+      Process.kill(:INT, solid_queue_pid) if solid_queue_pid
+      Process.wait(solid_queue_pid)
+    rescue Errno::ECHILD, Errno::ESRCH
+    end
+
+    def monitor_puma
+      monitor(:puma_dead?, "Detected Puma has gone away, stopping Solid Queue...")
+    end
+
+    def monitor_solid_queue
+      monitor(:solid_queue_dead?, "Detected Solid Queue has gone away, stopping Puma...")
+    end
+
+    def monitor(process_dead, message)
+      loop do
+        if send(process_dead)
+          log message
+          Process.kill(:INT, $$)
+          break
+        end
+        sleep 2
+      end
+    end
+
+    def solid_queue_dead?
+      Process.waitpid(solid_queue_pid, Process::WNOHANG)
+      false
+    rescue Errno::ECHILD, Errno::ESRCH
+      true
+    end
+
+    def puma_dead?
+      Process.ppid != puma_pid
+    end
+
+    def log(...)
+      log_writer.log(...)
+    end
+end