ActiveRecord's connection pool is based on threads. Since we are working with EM and a single thread, multiple fiber design, we need to provide our own connection pool that keys off of Fiber.current so that different fibers running in the same thread don't try to use the same connection.
# File lib/active_record/fiber_patches.rb, line 52 def initialize(spec) @spec = spec # The cache of reserved connections mapped to threads @reserved_connections = {} # The mutex used to synchronize pool access @connection_mutex = FiberedMonitor.new @queue = @connection_mutex.new_cond # default 5 second timeout unless on ruby 1.9 @timeout = spec.config[:wait_timeout] || 5 # default max pool size to 5 @size = (spec.config[:pool] && spec.config[:pool].to_i) || 5 @connections = [] @checked_out = [] @automatic_reconnect = true @tables = {} @columns = Hash.new do |h, table_name| h[table_name] = with_connection do |conn| # Fetch a list of columns conn.columns(table_name, "#{table_name} Columns").tap do |columns| # set primary key information columns.each do |column| column.primary = column.name == primary_keys[table_name] end end end end @columns_hash = Hash.new do |h, table_name| h[table_name] = Hash[columns[table_name].map { |col| [col.name, col] }] end @primary_keys = Hash.new do |h, table_name| h[table_name] = with_connection do |conn| table_exists?(table_name) ? conn.primary_key(table_name) : 'id' end end end
# File lib/active_record/fiber_patches.rb, line 100 def clear_stale_cached_connections! cache = @reserved_connections keys = Set.new(cache.keys) ActiveRecord::ConnectionAdapters.fiber_pools.each do |pool| pool.busy_fibers.each_pair do |object_id, fiber| keys.delete(object_id) end end keys.each do |key| next unless cache.has_key?(key) checkin cache[key] cache.delete(key) end end