Class: ActiveRecord::ConnectionAdapters::ConnectionHandler

Inherits:
Object
  • Object
show all
Defined in:
lib/active_record/connection_adapters/abstract/connection_pool.rb

Overview

ConnectionHandler is a collection of ConnectionPool objects. It is used for keeping separate connection pools that connect to different databases.

For example, suppose that you have 5 models, with the following hierarchy:

class Author < ActiveRecord::Base
end

class BankAccount < ActiveRecord::Base
end

class Book < ActiveRecord::Base
  establish_connection :library_db
end

class ScaryBook < Book
end

class GoodBook < Book
end

And a database.yml that looked like this:

development:
  database: my_application
  host: localhost

library_db:
  database: library
  host: some.library.org

Your primary database in the development environment is “my_application” but the Book model connects to a separate database called “library_db” (this can even be a database on a different machine).

Book, ScaryBook and GoodBook will all use the same connection pool to “library_db” while Author, BankAccount, and any other models you create will use the default connection pool to “my_application”.

The various connection pools are managed by a single instance of ConnectionHandler accessible via ActiveRecord::Base.connection_handler. All Active Record models use this handler to determine the connection pool that they should use.

The ConnectionHandler class is not coupled with the Active models, as it has no knowledge about the model. The model needs to pass a specification name to the handler, in order to look up the correct connection pool.

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ ConnectionHandler

Returns a new instance of ConnectionHandler.



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1016

def initialize
  # These caches are keyed by spec.name (ConnectionSpecification#name).
  @owner_to_pool = ConnectionHandler.create_owner_to_pool

  # Backup finalizer: if the forked child never needed a pool, the above
  # early discard has not occurred
  ObjectSpace.define_finalizer self, ConnectionHandler.unowned_pool_finalizer(@owner_to_pool)
end

Class Method Details

.create_owner_to_pool ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 994

def self.create_owner_to_pool # :nodoc:
  Concurrent::Map.new(initial_capacity: 2) do |h, k|
    # Discard the parent's connection pools immediately; we have no need
    # of them
    discard_unowned_pools(h)

    h[k] = Concurrent::Map.new(initial_capacity: 2)
  end
end

.discard_unowned_pools(pid_map) ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1010

def self.discard_unowned_pools(pid_map) # :nodoc:
  pid_map.each do |pid, pools|
    pools.values.compact.each(&:discard!) unless pid == Process.pid
  end
end

.unowned_pool_finalizer(pid_map) ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1004

def self.unowned_pool_finalizer(pid_map) # :nodoc:
  lambda do |_|
    discard_unowned_pools(pid_map)
  end
end

Instance Method Details

#active_connections? ⇒ Boolean

Returns true if there are any active connections among the connection pools that the ConnectionHandler is managing.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1074

def active_connections?
  connection_pool_list.any?(&:active_connection?)
end

#clear_active_connections! ⇒ Object

Returns any connections in use by the current thread back to the pool, and also returns connections to the pool cached by threads that are no longer alive.



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1081

def clear_active_connections!
  connection_pool_list.each(&:release_connection)
end

#clear_all_connections! ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1092

def clear_all_connections!
  connection_pool_list.each(&:disconnect!)
end

#clear_reloadable_connections! ⇒ Object

Clears the cache which maps classes.

See ConnectionPool#clear_reloadable_connections! for details.



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1088

def clear_reloadable_connections!
  connection_pool_list.each(&:clear_reloadable_connections!)
end

#connected?(spec_name) ⇒ Boolean

Returns true if a connection that’s accessible to this class has already been opened.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1124

def connected?(spec_name)
  pool = retrieve_connection_pool(spec_name)
  pool && pool.connected?
end

#connection_pool_list ⇒ Object Also known as: connection_pools 



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1045

def connection_pool_list
  owner_to_pool.values.compact
end

#establish_connection(config) ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1050

def establish_connection(config)
  resolver = ConnectionSpecification::Resolver.new(Base.configurations)
  spec = resolver.spec(config)

  remove_connection(spec.name)

  message_bus = ActiveSupport::Notifications.instrumenter
  payload = {
    connection_id: object_id
  }
  if spec
    payload[:spec_name] = spec.name
    payload[:config] = spec.config
  end

  message_bus.instrument("!connection.active_record", payload) do
    owner_to_pool[spec.name] = ConnectionAdapters::ConnectionPool.new(spec)
  end

  owner_to_pool[spec.name]
end

#flush_idle_connections! ⇒ Object

Disconnects all currently idle connections.

See ConnectionPool#flush! for details.



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1099

def flush_idle_connections!
  connection_pool_list.each(&:flush!)
end

#prevent_writes ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1025

def prevent_writes # :nodoc:
  Thread.current[:prevent_writes]
end

#prevent_writes=(prevent_writes) ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1029

def prevent_writes=(prevent_writes) # :nodoc:
  Thread.current[:prevent_writes] = prevent_writes
end

#remove_connection(spec_name) ⇒ Object

Remove the connection for this class. This will close the active connection and the defined connection (if they exist). The result can be used as an argument for #establish_connection, for easily re-establishing the connection.



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1133

def remove_connection(spec_name)
  if pool = owner_to_pool.delete(spec_name)
    pool.automatic_reconnect = false
    pool.disconnect!
    pool.spec.config
  end
end

#retrieve_connection(spec_name) ⇒ Object

Locate the connection of the nearest super class. This can be an active or defined connection: if it is the latter, it will be opened and set as the active connection for the class it was defined for (not necessarily the current class).



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1107

def retrieve_connection(spec_name) #:nodoc:
  pool = retrieve_connection_pool(spec_name)

  unless pool
    # multiple database application
    if ActiveRecord::Base.connection_handler != ActiveRecord::Base.default_connection_handler
      raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found for the '#{ActiveRecord::Base.current_role}' role."
    else
      raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found."
    end
  end

  pool.connection
end

#retrieve_connection_pool(spec_name) ⇒ Object

Retrieving the connection pool happens a lot, so we cache it in @owner_to_pool. This makes retrieving the connection pool O(1) once the process is warm. When a connection is established or removed, we invalidate the cache.



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1144

def retrieve_connection_pool(spec_name)
  owner_to_pool.fetch(spec_name) do
    # Check if a connection was previously established in an ancestor process,
    # which may have been forked.
    if ancestor_pool = pool_from_any_process_for(spec_name)
      # A connection was established in an ancestor process that must have
      # subsequently forked. We can't reuse the connection, but we can copy
      # the specification and establish a new connection with it.
      establish_connection(ancestor_pool.spec.to_hash).tap do |pool|
        pool.schema_cache = ancestor_pool.schema_cache if ancestor_pool.schema_cache
      end
    else
      owner_to_pool[spec_name] = nil
    end
  end
end

#while_preventing_writes(enabled = true) ⇒ Object

Prevent writing to the database regardless of role.

In some cases you may want to prevent writes to the database even if you are on a database that can write. ‘while_preventing_writes` will prevent writes to the database for the duration of the block.



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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1038

def while_preventing_writes(enabled = true)
  original, self.prevent_writes = self.prevent_writes, enabled
  yield
ensure
  self.prevent_writes = original
end