force unicorn to terminate before restarting

lib/capistrano/tasks/unicorn.cap

@@ -0,0 +1,16 @@
+namespace :unicorn do
+  desc "Terminate unicorn processes (blocks until complete)"
+  task :terminate do
+    on roles(:app) do
+      n = 0
+      while n < 10 && !capture("pgrep -f unicorn").blank?
+        execute "pgrep -f unicorn | xargs -SIGTERM"
+        n += 1
+      end
+
+      if n == 10
+        execute "pgrep -f unicorn | xargs -SIGKILL"
+      end
+    end
+  end
+end