MySQL specific gaplock protection is configurable

Instead of depending on the name of the ActiveRecord adapter to identify if the database is MySQL, gaplock protection is configurable, as suggested by @jurre on #399

.circleci/config.yml

@@ -38,6 +38,7 @@ jobs:
           - RAILS_VERSION=5.2.4
           - DATABASE_URL=mysql2://[email protected]/statesman_test
           - DATABASE_DEPENDENCY_PORT=3306
+          - GAPLOCK_PROTECTION=true
       - image: circleci/mysql:5.7.18
         environment:
           - MYSQL_ALLOW_EMPTY_PASSWORD=true
@@ -66,6 +67,7 @@ jobs:
           - RAILS_VERSION=6.0.2
           - DATABASE_URL=mysql2://[email protected]/statesman_test
           - DATABASE_DEPENDENCY_PORT=3306
+          - GAPLOCK_PROTECTION=true
       - image: circleci/mysql:5.7.18
         environment:
           - MYSQL_ALLOW_EMPTY_PASSWORD=true
@@ -93,6 +95,7 @@ jobs:
           - RAILS_VERSION=master
           - DATABASE_URL=mysql2://[email protected]/statesman_test
           - DATABASE_DEPENDENCY_PORT=3306
+          - GAPLOCK_PROTECTION=true
       - image: circleci/mysql:5.7.18
         environment:
           - MYSQL_ALLOW_EMPTY_PASSWORD=true
@@ -122,6 +125,7 @@ jobs:
           - RAILS_VERSION=6.0.2
           - DATABASE_URL=mysql2://[email protected]/statesman_test
           - DATABASE_DEPENDENCY_PORT=3306
+          - GAPLOCK_PROTECTION=true
       - image: circleci/mysql:5.7.18
         environment:
           - MYSQL_ALLOW_EMPTY_PASSWORD=true
@@ -149,6 +153,7 @@ jobs:
           - RAILS_VERSION=master
           - DATABASE_URL=mysql2://[email protected]/statesman_test
           - DATABASE_DEPENDENCY_PORT=3306
+          - GAPLOCK_PROTECTION=true
       - image: circleci/mysql:5.7.18
         environment:
           - MYSQL_ALLOW_EMPTY_PASSWORD=true

lib/statesman.rb

@@ -23,11 +23,18 @@ module Adapters
   #   end
   #
   def self.configure(&block)
-    config = Config.new(block)
-    @storage_adapter = config.adapter_class
+    @config = Config.new(block)
   end
 
   def self.storage_adapter
-    @storage_adapter || Adapters::Memory
+    config.adapter_class || Adapters::Memory
+  end
+
+  def self.gaplock_protection_enabled?
+    !!config.gaplock_protection_enabled
+  end
+
+  def self.config
+    @config
   end
 end

lib/statesman/adapters/active_record.rb

@@ -74,7 +74,7 @@ def create_transition(from, to, metadata)
         ::ActiveRecord::Base.transaction(requires_new: true) do
           @observer.execute(:before, from, to, transition)
 
-          if db_mysql?
+          if gaplock_protection_enabled?
             # We save the transition first with most_recent falsy, then mark most_recent
             # true after to avoid letting MySQL acquire a next-key lock which can cause
             # deadlocks.
@@ -136,7 +136,7 @@ def update_most_recents(most_recent_id = nil)
         # MySQL will validate index constraints across the intermediate result of an
         # update. This means we must order our update to deactivate the previous
         # most_recent before setting the new row to be true.
-        update.order(transition_table[:most_recent].desc) if db_mysql?
+        update.order(transition_table[:most_recent].desc) if gaplock_protection_enabled?
 
         ::ActiveRecord::Base.connection.update(update.to_sql)
       end
@@ -292,8 +292,8 @@ def updated_column_and_timestamp
         ]
       end
 
-      def db_mysql?
-        ::ActiveRecord::Base.connection.adapter_name.downcase.starts_with?("mysql")
+      def gaplock_protection_enabled?
+        Statesman.gaplock_protection_enabled?
       end
 
       def db_true

lib/statesman/config.rb

@@ -5,14 +5,19 @@
 
 module Statesman
   class Config
-    attr_reader :adapter_class
+    attr_reader :adapter_class, :gaplock_protection_enabled
 
     def initialize(block = nil)
+      @gaplock_protection_enabled = false
       instance_eval(&block) unless block.nil?
     end
 
     def storage_adapter(adapter_class)
       @adapter_class = adapter_class
     end
+
+    def mysql_gaplock_protection(gaplock_protection)
+      @gaplock_protection_enabled = gaplock_protection
+    end
   end
 end

spec/spec_helper.rb

@@ -15,6 +15,11 @@
 require "rspec/its"
 require "pry"
 
+Statesman.configure do
+  # These ENV vars are only set on the MySQL builds
+  mysql_gaplock_protection ENV.has_key?("GAPLOCK_PROTECTION")
+end
+
 RSpec.configure do |config|
   config.raise_errors_for_deprecations!
   config.mock_with(:rspec) { |mocks| mocks.verify_partial_doubles = true }