Add a before_fork callback called before forking new molds and new …

…workers.

Fix: #76

docs/CONFIGURATION.md

@@ -284,6 +284,16 @@ after_monitor_ready do |server|
 end
 ```
 
+### `before_fork`
+
+Called by the mold before forking a new workers, and by workers before they spawn a new mold.
+
+```ruby
+before_fork do |server|
+  server.logger.info("About to fork, closing connections!")
+end
+```
+
 ### `after_mold_fork`
 
 ```ruby

lib/pitchfork/configurator.rb

@@ -37,6 +37,7 @@ class Configurator
       :timeout => 22,
       :logger => default_logger,
       :worker_processes => 1,
+      :before_fork => nil,
       :after_worker_fork => lambda { |server, worker|
         server.logger.info("worker=#{worker.nr} gen=#{worker.generation} pid=#{$$} spawned")
       },
@@ -133,6 +134,10 @@ def logger(obj)
       set[:logger] = obj
     end
 
+    def before_fork(*args, &block)
+      set_hook(:before_fork, block_given? ? block : args[0], 1)
+    end
+
     def after_worker_fork(*args, &block)
       set_hook(:after_worker_fork, block_given? ? block : args[0])
     end

lib/pitchfork/http_server.rb

@@ -75,7 +75,7 @@ def extend_deadline(extra_time)
 
     # :stopdoc:
     attr_accessor :app, :timeout, :soft_timeout, :cleanup_timeout, :spawn_timeout, :worker_processes,
-                  :after_worker_fork, :after_mold_fork,
+                  :before_fork, :after_worker_fork, :after_mold_fork,
                   :listener_opts, :children,
                   :orig_app, :config, :ready_pipe,
                   :default_middleware, :early_hints
@@ -563,6 +563,7 @@ def spawn_worker(worker, detach:)
       # reason it gets stuck before reaching the worker loop,
       # the monitor process will kill it.
       worker.update_deadline(@spawn_timeout)
+      @before_fork&.call(self)
       Pitchfork.fork_sibling do
         worker.pid = Process.pid
 
@@ -870,6 +871,8 @@ def worker_loop(worker)
     def spawn_mold(current_generation)
       return false unless @promotion_lock.try_lock
 
+      @before_fork&.call(self)
+
       begin
         Pitchfork.fork_sibling do
           mold = Worker.new(nil, pid: Process.pid, generation: current_generation)

test/integration/test_configuration.rb

@@ -26,6 +26,22 @@ def test_after_request_complete
     assert_clean_shutdown(pid)
   end
 
+  def test_before_fork
+    addr, port = unused_port
+
+    pid = spawn_server(app: File.join(ROOT, "test/integration/env.ru"), config: <<~CONFIG)
+      listen "#{addr}:#{port}"
+      worker_processes 1
+
+      before_fork do |server|
+        $stderr.puts "[before_fork]"
+      end
+    CONFIG
+
+    assert_healthy("http://#{addr}:#{port}")
+    assert_stderr("[before_fork]")
+    assert_clean_shutdown(pid)
+  end
   def test_before_worker_exit
     addr, port = unused_port