FIX: pool drainer to use Rails 5.2 implementation

old implementation did not reap abandoned connections

lib/discourse.rb

@@ -500,6 +500,9 @@ module Discourse
     ObjectSpace.each_object(ActiveRecord::ConnectionAdapters::ConnectionPool) { |pool| pools << pool }
 
     pools.each do |pool|
+      # reap recovers connections that were aborted
+      # eg a thread died or a dev forgot to check it in
+      pool.reap
       pool.drain(idle.seconds, max_age.seconds)
     end
   end

lib/freedom_patches/pool_drainer.rb

@@ -25,31 +25,23 @@ class ActiveRecord::ConnectionAdapters::ConnectionPool
   # drain all idle connections
   # if idle_time is specified only connections idle for N seconds will be drained
   def drain(idle_time = nil, max_age = nil)
-    synchronize do
-      if @available && @connections
-        @available.clear
-        @connections.delete_if do |conn|
-          try_drain?(conn, idle_time, max_age)
-        end
+    return if !(@connections && @available)
 
-        @connections.each do |conn|
-          @available.add conn if !conn.in_use?
-        end
+    idle_connections = synchronize do
+      @connections.select do |conn|
+        !conn.in_use? && ((idle_time && conn.last_use <= idle_time.seconds.ago) || (max_age && conn.first_use < max_age.seconds.ago))
+      end.each do |conn|
+        conn.lease
+
+        @available.delete conn
+        @connections.delete conn
       end
     end
 
-  end
-
-  private
-
-  def try_drain?(conn, idle_time, max_age)
-    if !conn.in_use?
-      if !idle_time || conn.last_use < idle_time.seconds.ago || (max_age && conn.first_use < max_age.seconds.ago)
+    idle_connections.each do |conn|
       conn.disconnect!
-        return true
-      end
     end
 
-    false
   end
+
 end

spec/components/freedom_patches/pool_drainer_spec.rb

@@ -6,7 +6,10 @@ describe 'pool drainer' do
   end
 
   it 'can correctly drain the connection pool' do
-    pool.drain
+
+    pool.reap
+    pool.drain(0)
+
     old = pool.connections.length
     expect(old).to eq(1)
 
@@ -16,7 +19,9 @@ describe 'pool drainer' do
     end.join
 
     expect(pool.connections.length).to eq(old + 1)
-    pool.drain
+
+    freeze_time 1.second.from_now
+    pool.drain(0)
     expect(pool.connections.length).to eq(old)
   end