From 2b8d4508e51b85c6b36594aec2ebcbc269ee3daf Mon Sep 17 00:00:00 2001
From: Sam <sam.saffron@gmail.com>
Date: Thu, 23 Nov 2017 15:48:47 +1100
Subject: [PATCH] PERF: stop running background work between requests

Use a dedicated thread to run Scheduler::Defer

This avoids blocking of a worker during operations that require waiting.

In particular uploads risked blocking a unicorn.

This also add a queue "length" that discourse prometheus consumes.
---
 config/initializers/099-defer.rb        |  1 +
 config/initializers/099-unicorn.rb      |  7 -------
 lib/scheduler/defer.rb                  | 14 ++++----------
 spec/components/scheduler/defer_spec.rb |  2 ++
 4 files changed, 7 insertions(+), 17 deletions(-)
 create mode 100644 config/initializers/099-defer.rb
 delete mode 100644 config/initializers/099-unicorn.rb

diff --git a/config/initializers/099-defer.rb b/config/initializers/099-defer.rb
new file mode 100644
index 00000000000..9d020433c1d
--- /dev/null
+++ b/config/initializers/099-defer.rb
@@ -0,0 +1 @@
+require_dependency 'scheduler/defer'
diff --git a/config/initializers/099-unicorn.rb b/config/initializers/099-unicorn.rb
deleted file mode 100644
index e6152b69d70..00000000000
--- a/config/initializers/099-unicorn.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-require_dependency 'scheduler/defer'
-
-if defined? Unicorn::HttpServer
-  ObjectSpace.each_object(Unicorn::HttpServer) do |s|
-    s.extend(Scheduler::Defer::Unicorn)
-  end
-end
diff --git a/lib/scheduler/defer.rb b/lib/scheduler/defer.rb
index 6346b16dae1..e63cde145a0 100644
--- a/lib/scheduler/defer.rb
+++ b/lib/scheduler/defer.rb
@@ -8,6 +8,10 @@ module Scheduler
       @thread = nil
     end
 
+    def length
+      @queue.length
+    end
+
     def pause
       stop!
       @paused = true
@@ -80,16 +84,6 @@ module Scheduler
   end
 
   class Defer
-
-    module Unicorn
-      def process_client(client)
-        Defer.pause
-        super(client)
-        Defer.do_all_work
-        Defer.resume
-      end
-    end
-
     extend Deferrable
     initialize
   end
diff --git a/spec/components/scheduler/defer_spec.rb b/spec/components/scheduler/defer_spec.rb
index c00829b3c34..e7f57315e6f 100644
--- a/spec/components/scheduler/defer_spec.rb
+++ b/spec/components/scheduler/defer_spec.rb
@@ -31,6 +31,8 @@ describe Scheduler::Defer do
       x = 2
     end
 
+    expect(@defer.length).to eq(1)
+
     @defer.do_all_work
 
     expect(x).to eq(2)