Simplify termination handling for forked supervisor

No need to raise exceptions and rescue them, we can just check if a stop
has been requested and terminate accordingly.

Author: rosa

lib/solid_queue/processes/runnable.rb

@@ -7,7 +7,7 @@ module Runnable
     attr_writer :mode
 
     def start
-      @stopping = false
+      @stopped = false
 
       SolidQueue.instrument(:start_process, process: self) do
         run_callbacks(:boot) { boot }
@@ -21,7 +21,7 @@ def start
     end
 
     def stop
-      @stopping = true
+      @stopped = true
       @thread&.join
     end
 
@@ -40,15 +40,15 @@ def boot
       end
 
       def shutting_down?
-        stopping? || supervisor_went_away? || finished?
+        stopped? || supervisor_went_away? || finished?
       end
 
       def run
         raise NotImplementedError
       end
 
-      def stopping?
-        @stopping
+      def stopped?
+        @stopped
       end
 
       def finished?

lib/solid_queue/supervisor.rb

@@ -4,9 +4,6 @@ module SolidQueue
   class Supervisor < Processes::Base
     include Maintenance
 
-    class GracefulTerminationRequested < Interrupt; end
-    class ImmediateTerminationRequested < Interrupt; end
-
     class << self
       def start(mode: :fork, load_configuration_from: nil)
         SolidQueue.supervisor = true
@@ -26,26 +23,35 @@ def start
       start_processes
       launch_maintenance_task
 
-      supervise
-    rescue GracefulTerminationRequested
-      terminate_gracefully
-    rescue ImmediateTerminationRequested
-      terminate_immediately
+      loop do
+        break if stopped?
+
+        supervise
+      end
     ensure
       run_callbacks(:shutdown) { shutdown }
     end
 
+    def stop
+      @stopped = true
+    end
+
     private
       attr_reader :configuration
 
       def boot
+        @stopped = false
         sync_std_streams
       end
 
       def start_processes
         configuration.processes.each { |configured_process| start_process(configured_process) }
       end
 
+      def stopped?
+        @stopped
+      end
+
       def supervise
         raise NotImplementedError
       end
@@ -54,12 +60,6 @@ def start_process(configured_process)
         raise NotImplementedError
       end
 
-      def terminate_gracefully
-      end
-
-      def terminate_immediately
-      end
-
       def shutdown
         stop_maintenance_task
       end

lib/solid_queue/supervisor/fork_supervisor.rb

@@ -17,10 +17,10 @@ def kind
       attr_reader :forks
 
       def supervise
-        loop do
-          procline "supervising #{forks.keys.join(", ")}"
+        procline "supervising #{forks.keys.join(", ")}"
+        process_signal_queue
 
-          process_signal_queue
+        unless stopped?
           reap_and_replace_terminated_forks
           interruptible_sleep(1.second)
         end

lib/solid_queue/supervisor/signals.rb

@@ -37,22 +37,16 @@ def process_signal_queue
         def handle_signal(signal)
           case signal
           when :TERM, :INT
-            request_graceful_termination
+            stop
+            terminate_gracefully
           when :QUIT
-            request_immediate_termination
+            stop
+            terminate_immediately
           else
             SolidQueue.instrument :unhandled_signal_error, signal: signal
           end
         end
 
-        def request_graceful_termination
-          raise GracefulTerminationRequested
-        end
-
-        def request_immediate_termination
-          raise ImmediateTerminationRequested
-        end
-
         def signal_processes(pids, signal)
           pids.each do |pid|
             signal_process pid, signal