Make many parts of Rails lazy. In order to facilitate this,

add lazy_load_hooks.rb, which allows us to declare code that
should be run at some later time. For instance, this allows
us to defer requiring ActiveRecord::Base at boot time purely
to apply configuration. Instead, we register a hook that should
apply configuration once ActiveRecord::Base is loaded.

With these changes, brings down total boot time of a
new app to 300ms in production and 400ms in dev.

TODO: rename base_hook

3 files changed, 197 insertions, 180 deletions

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 042a67b490..52587ef251 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -13,172 +13,10 @@ require 'active_support/core_ext/hash/slice'
 require 'active_support/core_ext/string/behavior'
 require 'active_support/core_ext/object/singleton_class'
 require 'active_support/core_ext/module/delegation'
+require 'arel'
+require 'active_record/errors'
 
 module ActiveRecord #:nodoc:
-  # Generic Active Record exception class.
-  class ActiveRecordError < StandardError
-  end
-
-  # Raised when the single-table inheritance mechanism fails to locate the subclass
-  # (for example due to improper usage of column that +inheritance_column+ points to).
-  class SubclassNotFound < ActiveRecordError #:nodoc:
-  end
-
-  # Raised when an object assigned to an association has an incorrect type.
-  #
-  #   class Ticket < ActiveRecord::Base
-  #     has_many :patches
-  #   end
-  #
-  #   class Patch < ActiveRecord::Base
-  #     belongs_to :ticket
-  #   end
-  #
-  #   # Comments are not patches, this assignment raises AssociationTypeMismatch.
-  #   @ticket.patches << Comment.new(:content => "Please attach tests to your patch.")
-  class AssociationTypeMismatch < ActiveRecordError
-  end
-
-  # Raised when unserialized object's type mismatches one specified for serializable field.
-  class SerializationTypeMismatch < ActiveRecordError
-  end
-
-  # Raised when adapter not specified on connection (or configuration file <tt>config/database.yml</tt> misses adapter field).
-  class AdapterNotSpecified < ActiveRecordError
-  end
-
-  # Raised when Active Record cannot find database adapter specified in <tt>config/database.yml</tt> or programmatically.
-  class AdapterNotFound < ActiveRecordError
-  end
-
-  # Raised when connection to the database could not been established (for example when <tt>connection=</tt> is given a nil object).
-  class ConnectionNotEstablished < ActiveRecordError
-  end
-
-  # Raised when Active Record cannot find record by given id or set of ids.
-  class RecordNotFound < ActiveRecordError
-  end
-
-  # Raised by ActiveRecord::Base.save! and ActiveRecord::Base.create! methods when record cannot be
-  # saved because record is invalid.
-  class RecordNotSaved < ActiveRecordError
-  end
-
-  # Raised when SQL statement cannot be executed by the database (for example, it's often the case for MySQL when Ruby driver used is too old).
-  class StatementInvalid < ActiveRecordError
-  end
-
-  # Raised when SQL statement is invalid and the application gets a blank result.
-  class ThrowResult < ActiveRecordError
-  end
-
-  # Parent class for all specific exceptions which wrap database driver exceptions
-  # provides access to the original exception also.
-  class WrappedDatabaseException < StatementInvalid
-    attr_reader :original_exception
-
-    def initialize(message, original_exception)
-      super(message)
-      @original_exception = original_exception
-    end
-  end
-
-  # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
-  class RecordNotUnique < WrappedDatabaseException
-  end
-
-  # Raised when a record cannot be inserted or updated because it references a non-existent record.
-  class InvalidForeignKey < WrappedDatabaseException
-  end
-
-  # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
-  # does not match number of expected variables.
-  #
-  # For example, in
-  #
-  #   Location.find :all, :conditions => ["lat = ? AND lng = ?", 53.7362]
-  #
-  # two placeholders are given but only one variable to fill them.
-  class PreparedStatementInvalid < ActiveRecordError
-  end
-
-  # Raised on attempt to save stale record. Record is stale when it's being saved in another query after
-  # instantiation, for example, when two users edit the same wiki page and one starts editing and saves
-  # the page before the other.
-  #
-  # Read more about optimistic locking in ActiveRecord::Locking module RDoc.
-  class StaleObjectError < ActiveRecordError
-  end
-
-  # Raised when association is being configured improperly or
-  # user tries to use offset and limit together with has_many or has_and_belongs_to_many associations.
-  class ConfigurationError < ActiveRecordError
-  end
-
-  # Raised on attempt to update record that is instantiated as read only.
-  class ReadOnlyRecord < ActiveRecordError
-  end
-
-  # ActiveRecord::Transactions::ClassMethods.transaction uses this exception
-  # to distinguish a deliberate rollback from other exceptional situations.
-  # Normally, raising an exception will cause the +transaction+ method to rollback
-  # the database transaction *and* pass on the exception. But if you raise an
-  # ActiveRecord::Rollback exception, then the database transaction will be rolled back,
-  # without passing on the exception.
-  #
-  # For example, you could do this in your controller to rollback a transaction:
-  #
-  #   class BooksController < ActionController::Base
-  #     def create
-  #       Book.transaction do
-  #         book = Book.new(params[:book])
-  #         book.save!
-  #         if today_is_friday?
-  #           # The system must fail on Friday so that our support department
-  #           # won't be out of job. We silently rollback this transaction
-  #           # without telling the user.
-  #           raise ActiveRecord::Rollback, "Call tech support!"
-  #         end
-  #       end
-  #       # ActiveRecord::Rollback is the only exception that won't be passed on
-  #       # by ActiveRecord::Base.transaction, so this line will still be reached
-  #       # even on Friday.
-  #       redirect_to root_url
-  #     end
-  #   end
-  class Rollback < ActiveRecordError
-  end
-
-  # Raised when attribute has a name reserved by Active Record (when attribute has name of one of Active Record instance methods).
-  class DangerousAttributeError < ActiveRecordError
-  end
-
-  # Raised when unknown attributes are supplied via mass assignment.
-  class UnknownAttributeError < NoMethodError
-  end
-
-  # Raised when an error occurred while doing a mass assignment to an attribute through the
-  # <tt>attributes=</tt> method. The exception has an +attribute+ property that is the name of the
-  # offending attribute.
-  class AttributeAssignmentError < ActiveRecordError
-    attr_reader :exception, :attribute
-    def initialize(message, exception, attribute)
-      @exception = exception
-      @attribute = attribute
-      @message = message
-    end
-  end
-
-  # Raised when there are multiple errors while doing a mass assignment through the +attributes+
-  # method. The exception has an +errors+ property that contains an array of AttributeAssignmentError
-  # objects, each corresponding to the error while assigning to an attribute.
-  class MultiparameterAssignmentErrors < ActiveRecordError
-    attr_reader :errors
-    def initialize(errors)
-      @errors = errors
-    end
-  end
-
   # Active Record objects don't specify their attributes directly, but rather infer them from the table definition with
   # which they're linked. Adding, removing, and changing attributes and their type is done directly in the database. Any change
   # is instantly reflected in the Active Record objects. The mapping that binds a given Active Record class to a certain
@@ -551,7 +389,7 @@ module ActiveRecord #:nodoc:
     class << self # Class methods
       def colorize_logging(*args)
         ActiveSupport::Deprecation.warn "ActiveRecord::Base.colorize_logging and " <<
-          "config.active_record.colorize_logging are deprecated. Please use " << 
+          "config.active_record.colorize_logging are deprecated. Please use " <<
           "Rails::LogSubscriber.colorize_logging or config.colorize_logging instead", caller
       end
       alias :colorize_logging= :colorize_logging
@@ -2401,8 +2239,10 @@ module ActiveRecord #:nodoc:
 
     include Aggregations, Transactions, Reflection, Serialization
 
+    NilClass.add_whiner(self) if NilClass.respond_to?(:add_whiner)
   end
 end
 
 # TODO: Remove this and make it work with LAZY flag
 require 'active_record/connection_adapters/abstract_adapter'
+ActiveRecord.run_base_hooks(ActiveRecord::Base)
\ No newline at end of file
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
new file mode 100644
index 0000000000..cf5ddca2ba
--- /dev/null
+++ b/activerecord/lib/active_record/errors.rb
@@ -0,0 +1,165 @@
+module ActiveRecord
+  # Generic Active Record exception class.
+  class ActiveRecordError < StandardError
+  end
+
+  # Raised when the single-table inheritance mechanism fails to locate the subclass
+  # (for example due to improper usage of column that +inheritance_column+ points to).
+  class SubclassNotFound < ActiveRecordError #:nodoc:
+  end
+
+  # Raised when an object assigned to an association has an incorrect type.
+  #
+  #   class Ticket < ActiveRecord::Base
+  #     has_many :patches
+  #   end
+  #
+  #   class Patch < ActiveRecord::Base
+  #     belongs_to :ticket
+  #   end
+  #
+  #   # Comments are not patches, this assignment raises AssociationTypeMismatch.
+  #   @ticket.patches << Comment.new(:content => "Please attach tests to your patch.")
+  class AssociationTypeMismatch < ActiveRecordError
+  end
+
+  # Raised when unserialized object's type mismatches one specified for serializable field.
+  class SerializationTypeMismatch < ActiveRecordError
+  end
+
+  # Raised when adapter not specified on connection (or configuration file <tt>config/database.yml</tt> misses adapter field).
+  class AdapterNotSpecified < ActiveRecordError
+  end
+
+  # Raised when Active Record cannot find database adapter specified in <tt>config/database.yml</tt> or programmatically.
+  class AdapterNotFound < ActiveRecordError
+  end
+
+  # Raised when connection to the database could not been established (for example when <tt>connection=</tt> is given a nil object).
+  class ConnectionNotEstablished < ActiveRecordError
+  end
+
+  # Raised when Active Record cannot find record by given id or set of ids.
+  class RecordNotFound < ActiveRecordError
+  end
+
+  # Raised by ActiveRecord::Base.save! and ActiveRecord::Base.create! methods when record cannot be
+  # saved because record is invalid.
+  class RecordNotSaved < ActiveRecordError
+  end
+
+  # Raised when SQL statement cannot be executed by the database (for example, it's often the case for MySQL when Ruby driver used is too old).
+  class StatementInvalid < ActiveRecordError
+  end
+
+  # Raised when SQL statement is invalid and the application gets a blank result.
+  class ThrowResult < ActiveRecordError
+  end
+
+  # Parent class for all specific exceptions which wrap database driver exceptions
+  # provides access to the original exception also.
+  class WrappedDatabaseException < StatementInvalid
+    attr_reader :original_exception
+
+    def initialize(message, original_exception)
+      super(message)
+      @original_exception = original_exception
+    end
+  end
+
+  # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
+  class RecordNotUnique < WrappedDatabaseException
+  end
+
+  # Raised when a record cannot be inserted or updated because it references a non-existent record.
+  class InvalidForeignKey < WrappedDatabaseException
+  end
+
+  # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
+  # does not match number of expected variables.
+  #
+  # For example, in
+  #
+  #   Location.find :all, :conditions => ["lat = ? AND lng = ?", 53.7362]
+  #
+  # two placeholders are given but only one variable to fill them.
+  class PreparedStatementInvalid < ActiveRecordError
+  end
+
+  # Raised on attempt to save stale record. Record is stale when it's being saved in another query after
+  # instantiation, for example, when two users edit the same wiki page and one starts editing and saves
+  # the page before the other.
+  #
+  # Read more about optimistic locking in ActiveRecord::Locking module RDoc.
+  class StaleObjectError < ActiveRecordError
+  end
+
+  # Raised when association is being configured improperly or
+  # user tries to use offset and limit together with has_many or has_and_belongs_to_many associations.
+  class ConfigurationError < ActiveRecordError
+  end
+
+  # Raised on attempt to update record that is instantiated as read only.
+  class ReadOnlyRecord < ActiveRecordError
+  end
+
+  # ActiveRecord::Transactions::ClassMethods.transaction uses this exception
+  # to distinguish a deliberate rollback from other exceptional situations.
+  # Normally, raising an exception will cause the +transaction+ method to rollback
+  # the database transaction *and* pass on the exception. But if you raise an
+  # ActiveRecord::Rollback exception, then the database transaction will be rolled back,
+  # without passing on the exception.
+  #
+  # For example, you could do this in your controller to rollback a transaction:
+  #
+  #   class BooksController < ActionController::Base
+  #     def create
+  #       Book.transaction do
+  #         book = Book.new(params[:book])
+  #         book.save!
+  #         if today_is_friday?
+  #           # The system must fail on Friday so that our support department
+  #           # won't be out of job. We silently rollback this transaction
+  #           # without telling the user.
+  #           raise ActiveRecord::Rollback, "Call tech support!"
+  #         end
+  #       end
+  #       # ActiveRecord::Rollback is the only exception that won't be passed on
+  #       # by ActiveRecord::Base.transaction, so this line will still be reached
+  #       # even on Friday.
+  #       redirect_to root_url
+  #     end
+  #   end
+  class Rollback < ActiveRecordError
+  end
+
+  # Raised when attribute has a name reserved by Active Record (when attribute has name of one of Active Record instance methods).
+  class DangerousAttributeError < ActiveRecordError
+  end
+
+  # Raised when unknown attributes are supplied via mass assignment.
+  class UnknownAttributeError < NoMethodError
+  end
+
+  # Raised when an error occurred while doing a mass assignment to an attribute through the
+  # <tt>attributes=</tt> method. The exception has an +attribute+ property that is the name of the
+  # offending attribute.
+  class AttributeAssignmentError < ActiveRecordError
+    attr_reader :exception, :attribute
+    def initialize(message, exception, attribute)
+      @exception = exception
+      @attribute = attribute
+      @message = message
+    end
+  end
+
+  # Raised when there are multiple errors while doing a mass assignment through the +attributes+
+  # method. The exception has an +errors+ property that contains an array of AttributeAssignmentError
+  # objects, each corresponding to the error while assigning to an attribute.
+  class MultiparameterAssignmentErrors < ActiveRecordError
+    attr_reader :errors
+    def initialize(errors)
+      @errors = errors
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index b38bd9a644..60addd46c6 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -24,31 +24,39 @@ module ActiveRecord
     log_subscriber ActiveRecord::Railties::LogSubscriber.new
 
     initializer "active_record.initialize_timezone" do
-      ActiveRecord::Base.time_zone_aware_attributes = true
-      ActiveRecord::Base.default_timezone = :utc
+      ActiveRecord.base_hook do
+        self.time_zone_aware_attributes = true
+        self.default_timezone = :utc
+      end
     end
 
     initializer "active_record.logger" do
-      ActiveRecord::Base.logger ||= ::Rails.logger
+      ActiveRecord.base_hook { self.logger ||= ::Rails.logger }
     end
 
     initializer "active_record.set_configs" do |app|
-      app.config.active_record.each do |k,v|
-        ActiveRecord::Base.send "#{k}=", v
+      ActiveRecord.base_hook do
+        app.config.active_record.each do |k,v|
+          send "#{k}=", v
+        end
       end
     end
 
     # This sets the database configuration from Configuration#database_configuration
     # and then establishes the connection.
     initializer "active_record.initialize_database" do |app|
-      ActiveRecord::Base.configurations = app.config.database_configuration
-      ActiveRecord::Base.establish_connection
+      ActiveRecord.base_hook do
+        self.configurations = app.config.database_configuration
+        establish_connection
+      end
     end
 
     # Expose database runtime to controller for logging.
     initializer "active_record.log_runtime" do |app|
       require "active_record/railties/controller_runtime"
-      ActionController::Base.send :include, ActiveRecord::Railties::ControllerRuntime
+      ActionController.base_hook do
+        include ActiveRecord::Railties::ControllerRuntime
+      end
     end
 
     # Setup database middleware after initializers have run
@@ -64,18 +72,22 @@ module ActiveRecord
     end
 
     initializer "active_record.load_observers" do
-      ActiveRecord::Base.instantiate_observers
+      ActiveRecord.base_hook { instantiate_observers }
 
-      ActionDispatch::Callbacks.to_prepare(:activerecord_instantiate_observers) do
-        ActiveRecord::Base.instantiate_observers
+      ActiveRecord.base_hook do
+        ActionDispatch::Callbacks.to_prepare(:activerecord_instantiate_observers) do
+          ActiveRecord::Base.instantiate_observers
+        end
       end
     end
 
     initializer "active_record.set_dispatch_hooks", :before => :set_clear_dependencies_hook do |app|
-      unless app.config.cache_classes
-        ActionDispatch::Callbacks.after do
-          ActiveRecord::Base.reset_subclasses
-          ActiveRecord::Base.clear_reloadable_connections!
+      ActiveRecord.base_hook do
+        unless app.config.cache_classes
+          ActionDispatch::Callbacks.after do
+            ActiveRecord::Base.reset_subclasses
+            ActiveRecord::Base.clear_reloadable_connections!
+          end
         end
       end
     end