class ActiveRecord::ConnectionAdapters::ConnectionHandler
ConnectionHandler is a collection of ConnectionPool objects. It is used for keeping separate connection pools for Active Record models that connect to different databases.
For example, suppose that you have 5 models, with the following hierarchy:
| +-- Book | | | +-- ScaryBook | +-- GoodBook +-- Author +-- BankAccount
Suppose that Book is to connect to a separate database (i.e. one other than the default database). Then Book, ScaryBook and GoodBook will all use the same connection pool. Likewise, Author and BankAccount will use the same connection pool. However, the connection pool used by Author/BankAccount is not the same as the one used by Book/ScaryBook/GoodBook.
Normally there is only a single ConnectionHandler instance, accessible via ActiveRecord::Base.connection_handler. Active Record models use this to determine the connection pool that they should use.
Public Class Methods
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 483 def initialize # These caches are keyed by klass.name, NOT klass. Keying them by klass # alone would lead to memory leaks in development mode as all previous # instances of the class would stay in memory. @owner_to_pool = ThreadSafe::Cache.new(:initial_capacity => 2) do |h,k| h[k] = ThreadSafe::Cache.new(:initial_capacity => 2) end @class_to_pool = ThreadSafe::Cache.new(:initial_capacity => 2) do |h,k| h[k] = ThreadSafe::Cache.new end end
Public Instance Methods
Returns true if there are any active connections among the connection pools that the ConnectionHandler is managing.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 515 def active_connections? connection_pool_list.any?(&:active_connection?) end
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.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 522 def clear_active_connections! connection_pool_list.each(&:release_connection) end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 531 def clear_all_connections! connection_pool_list.each(&:disconnect!) end
Clears the cache which maps classes.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 527 def clear_reloadable_connections! connection_pool_list.each(&:clear_reloadable_connections!) end
Returns true if a connection that's accessible to this class has already been opened.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 546 def connected?(klass) conn = retrieve_connection_pool(klass) conn && conn.connected? end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 495 def connection_pool_list owner_to_pool.values.compact end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 499 def connection_pools ActiveSupport::Deprecation.warn( "In the next release, this will return the same as #connection_pool_list. " "(An array of pools, rather than a hash mapping specs to pools.)" ) Hash[connection_pool_list.map { |pool| [pool.spec, pool] }] end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 507 def establish_connection(owner, spec) @class_to_pool.clear raise RuntimeError, "Anonymous class is not allowed." unless owner.name owner_to_pool[owner.name] = ConnectionAdapters::ConnectionPool.new(spec) end
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.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 555 def remove_connection(owner) if pool = owner_to_pool.delete(owner.name) @class_to_pool.clear pool.automatic_reconnect = false pool.disconnect! pool.spec.config end end
Retrieving the connection pool happens a lot so we cache it in @class_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.
Ideally we would use fetch here, as class_to_pool may sometimes be nil. However, benchmarking (gist.github.com/jonleighton/3552829) showed that fetch is significantly slower than []. So in the nil case, no caching will take place, but that's ok since the nil case is not the common one that we wish to optimise for.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 573 def retrieve_connection_pool(klass) class_to_pool[klass.name] ||= begin until pool = pool_for(klass) klass = klass.superclass break unless klass <= Base end class_to_pool[klass.name] = pool end end
Private Instance Methods
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 590 def class_to_pool @class_to_pool[Process.pid] end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 586 def owner_to_pool @owner_to_pool[Process.pid] end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 594 def pool_for(owner) owner_to_pool.fetch(owner.name) { if ancestor_pool = pool_from_any_process_for(owner) # 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 owner, ancestor_pool.spec else owner_to_pool[owner.name] = nil end } end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 607 def pool_from_any_process_for(owner) owner_to_pool = @owner_to_pool.values.find { |v| v[owner.name] } owner_to_pool && owner_to_pool[owner.name] end