Merge pull request #54 from Shopify/info-shutting-down

Implement Pitchfork::Info.shutting_down?

CHANGELOG.md

@@ -4,6 +4,7 @@
 - Implement `before_worker_exit` callback.
 - Make each mold and worker a process group leader.
 - Get rid of `Pitchfork::PrereadInput`.
+- Add `Pitchfork.shutting_down?` to allow health check endpoints to fail sooner on graceful shutdowns.
 - Treat `TERM` as graceful shutdown rather than quick shutdown.
 - Implement `after_worker_hard_timeout` callback.
 

lib/pitchfork/http_server.rb

@@ -338,9 +338,11 @@ def monitor_loop(sleep = true)
 
         master_sleep(sleep_time) if sleep
       when :QUIT, :TERM # graceful shutdown
+        SharedMemory.shutting_down!
         logger.info "#{message} received, starting graceful shutdown"
         return StopIteration
       when :INT # immediate shutdown
+        SharedMemory.shutting_down!
         logger.info "#{message} received, starting immediate shutdown"
         stop(false)
         return StopIteration
@@ -375,6 +377,7 @@ def monitor_loop(sleep = true)
     # Terminates all workers, but does not exit master process
     def stop(graceful = true)
       @respawn = false
+      SharedMemory.shutting_down!
       wait_for_pending_workers
       self.listeners = []
       limit = Pitchfork.time_now + timeout

lib/pitchfork/info.rb

@@ -15,6 +15,16 @@ def live_workers_count
           SharedMemory.worker_deadline(nr).value > now
         end
       end
+
+      # Returns true if the server is shutting down.
+      # This can be useful to implement health check endpoints, so they
+      # can fail immediately after TERM/QUIT/INT was received by the master
+      # process.
+      # Otherwise they may succeed while Pitchfork is draining requests causing
+      # more requests to be sent.
+      def shutting_down?
+        SharedMemory.shutting_down?
+      end
     end
   end
 end

lib/pitchfork/shared_memory.rb

@@ -8,8 +8,9 @@ module SharedMemory
 
     PER_DROP = Raindrops::PAGE_SIZE / Raindrops::SIZE
     CURRENT_GENERATION_OFFSET = 0
-    MOLD_TICK_OFFSET = 1
-    WORKER_TICK_OFFSET = 2
+    SHUTDOWN_OFFSET = 1
+    MOLD_TICK_OFFSET = 2
+    WORKER_TICK_OFFSET = 3
 
     DROPS = [Raindrops.new(PER_DROP)]
 
@@ -21,6 +22,14 @@ def current_generation=(value)
       DROPS[0][CURRENT_GENERATION_OFFSET] = value
     end
 
+    def shutting_down!
+      DROPS[0][SHUTDOWN_OFFSET] = 1
+    end
+
+    def shutting_down?
+      DROPS[0][SHUTDOWN_OFFSET] > 0
+    end
+
     class Field
       def initialize(offset)
         @drop = DROPS.fetch(offset / PER_DROP)