Add basic snapshot comparison for tracking memory leaks

Gemfile.lock

@@ -230,7 +230,7 @@ GEM
       metaclass (~> 0.0.1)
     mock_redis (0.13.2)
     moneta (0.8.0)
-    msgpack (0.5.10)
+    msgpack (0.5.11)
     multi_json (1.10.1)
     multi_xml (0.5.5)
     multipart-post (2.0.0)

app/controllers/admin/diagnostics_controller.rb

@@ -3,7 +3,25 @@ class Admin::DiagnosticsController < Admin::AdminController
   skip_before_filter :check_xhr
 
   def memory_stats
-    render text: memory_report(class_report: params.key?(:full)), content_type: Mime::TEXT
+    text = nil
+
+    if params.key?(:diff)
+      if !File.exists?(snapshot_filename)
+        text = "No initial snapshot exists"
+      else
+        filename = snapshot_filename + ".new"
+        snapshot_current_process(filename)
+
+        text = compare(snapshot_filename, filename)
+      end
+    elsif params.key?(:snapshot)
+      snapshot_current_process
+      text = "Writing snapshot to: #{snapshot_filename}\n\nTo get a diff use ?diff=1"
+    else
+      text = memory_report(class_report: params.key?(:full))
+    end
+
+    render text: text, content_type: Mime::TEXT
   end
 
   def dump_heap
@@ -24,6 +42,80 @@ class Admin::DiagnosticsController < Admin::AdminController
 
   protected
 
+  def compare(from, to)
+    from = Marshal::load(IO.binread(from));
+    to = Marshal::load(IO.binread(to));
+
+    diff = from - to
+
+    report = "#{diff.length} objects have leaked\n"
+
+
+    require 'objspace'
+    diff = diff.map do |id|
+      ObjectSpace._id2ref(id) rescue nil
+    end.compact!
+
+    report << "Summary:\n"
+
+    summary = {}
+    diff.each do |obj|
+      begin
+        summary[obj.class] ||= 0
+        summary[obj.class] += 1
+      rescue
+        # don't care
+      end
+    end
+
+    report << summary.sort{|a,b| b[1] <=> a[1]}[0..50].map{|k,v|
+      "#{k}: #{v}"
+    }.join("\n")
+
+    report << "\nSample Items:\n"
+
+    diff[0..5000].each do |v|
+      report << "#{v.class}: #{String === v ? v[0..300] : (40 + ObjectSpace.memsize_of(v)).to_s + " bytes"}\n" rescue nil
+    end
+
+    report
+  end
+
+  def snapshot_path
+    "#{Rails.root}/tmp/mem_snapshots"
+  end
+
+  def snapshot_filename
+    "#{snapshot_path}/#{Process.pid}.snapshot"
+  end
+
+  def snapshot_current_process(filename=nil)
+    filename ||= snapshot_filename
+    pid=fork do
+      snapshot(filename)
+    end
+
+    Process.wait(pid)
+  end
+
+  def snapshot(filename)
+    require 'objspace'
+    FileUtils.mkdir_p snapshot_path
+    object_ids = []
+
+    full_gc
+
+    ObjectSpace.each_object do |o|
+      begin
+        object_ids << o.object_id
+      rescue
+        # skip
+      end
+    end
+
+    IO.binwrite(filename, Marshal::dump(object_ids))
+  end
+
   def memory_report(opts={})
     begin
       # ruby 2.1
@@ -74,4 +166,26 @@ Classes:
 TEXT
 
   end
+
+
+  def full_gc
+    # gc start may not collect everything
+    GC.start while new_count = decreased_count(new_count)
+  end
+
+  def decreased_count(old)
+    count = count_objects
+    if !old || count < old
+      count
+    else
+      nil
+    end
+  end
+
+  def count_objects
+    i = 0
+    ObjectSpace.each_object do |obj|
+      i += 1
+    end
+  end
 end