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::Core.connection_handler. Active Record models use this to determine the connection pool that they should use.

Public Class Methods

new() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 488
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

active_connections?() click to toggle source

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 520
def active_connections?
  connection_pool_list.any?(&:active_connection?)
end
clear_active_connections!() click to toggle source

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 527
def clear_active_connections!
  connection_pool_list.each(&:release_connection)
end
clear_all_connections!() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 536
def clear_all_connections!
  connection_pool_list.each(&:disconnect!)
end
clear_reloadable_connections!() click to toggle source

Clears the cache which maps classes.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 532
def clear_reloadable_connections!
  connection_pool_list.each(&:clear_reloadable_connections!)
end
connected?(klass) click to toggle source

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 551
def connected?(klass)
  conn = retrieve_connection_pool(klass)
  conn && conn.connected?
end
connection_pool_list() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 500
def connection_pool_list
  owner_to_pool.values.compact
end
connection_pools() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 504
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
establish_connection(owner, spec) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 512
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_connection(owner) click to toggle source

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 560
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
retrieve_connection_pool(klass) click to toggle source

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 578
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

class_to_pool() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 595
def class_to_pool
  @class_to_pool[Process.pid]
end
owner_to_pool() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 591
def owner_to_pool
  @owner_to_pool[Process.pid]
end
pool_for(owner) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 599
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
pool_from_any_process_for(owner) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 612
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