Merge pull request #36296 from jhawthorn/dont_fear_the_reaper

Use a single thread for all ConnectionPool Reapers

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -294,15 +294,33 @@ module ActiveRecord
           @frequency = frequency
         end
 
-        def run
-          return unless frequency && frequency > 0
-          Thread.new(frequency, pool) { |t, p|
+        @@mutex = Mutex.new
+        @@pools = {}
+
+        def self.register_pool(pool, frequency) # :nodoc:
+          @@mutex.synchronize do
+            if @@pools.key?(frequency)
+              @@pools[frequency] << pool
+            else
+              @@pools[frequency] = [pool]
+              Thread.new(frequency) do |t|
                 loop do
                   sleep t
+                  @@mutex.synchronize do
+                    @@pools[frequency].each do |p|
                       p.reap
                       p.flush
                     end
-          }
+                  end
+                end
+              end
+            end
+          end
+        end
+
+        def run
+          return unless frequency && frequency > 0
+          self.class.register_pool(pool, frequency)
         end
       end