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require 'monitor'
require 'set'
module ActiveRecord
module ConnectionAdapters
# Connection pool base class and ActiveRecord database connections.
class ConnectionPool
# Factory method for connection pools.
# Determines pool type to use based on contents of connection specification.
# FIXME: specification configuration TBD.
def self.create(spec)
ConnectionPerThread.new(spec)
end
delegate :verification_timeout, :to => "::ActiveRecord::Base"
attr_reader :spec
def initialize(spec)
@spec = spec
# The cache of reserved connections mapped to threads
@reserved_connections = {}
# The mutex used to synchronize pool access
@connection_mutex = Monitor.new
end
# Retrieve the connection associated with the current thread, or call
# #checkout to obtain one if necessary.
#
# #connection can be called any number of times; the connection is
# held in a hash keyed by the thread id.
def connection
if conn = @reserved_connections[active_connection_name]
conn.verify!(verification_timeout)
conn
else
@reserved_connections[active_connection_name] = checkout
end
end
# Signal that the thread is finished with the current connection.
# #release_thread_connection releases the connection-thread association
# and returns the connection to the pool.
def release_thread_connection
conn = @reserved_connections.delete(active_connection_name)
checkin conn if conn
end
# Reserve a connection, and yield it to a block. Ensure the connection is
# checked back in when finished.
def with_connection
conn = checkout
yield conn
ensure
checkin conn
end
# Returns true if a connection has already been opened.
def connected?
!connections.empty?
end
# Disconnect all connections in the pool.
def disconnect!
@reserved_connections.each do |name,conn|
checkin conn
end
connections.each do |conn|
conn.disconnect!
end
@reserved_connections = {}
end
# Clears the cache which maps classes
def clear_reloadable_connections!
@reserved_connections.each do |name, conn|
checkin conn
end
@reserved_connections = {}
connections.each do |conn|
if conn.requires_reloading?
conn.disconnect!
remove_connection conn
end
end
end
# Verify active connections.
def verify_active_connections! #:nodoc:
remove_stale_cached_threads!(@reserved_connections) do |name, conn|
checkin conn
end
connections.each do |connection|
connection.verify!(verification_timeout)
end
end
# Check-out a database connection from the pool.
def checkout
raise NotImplementedError, "checkout is an abstract method"
end
# Check-in a database connection back into the pool.
def checkin(connection)
raise NotImplementedError, "checkin is an abstract method"
end
def remove_connection(conn)
raise NotImplementedError, "remove_connection is an abstract method"
end
private :remove_connection
# Array containing all connections (reserved or available) in the pool.
def connections
raise NotImplementedError, "connections is an abstract method"
end
private :connections
synchronize :connection, :release_thread_connection, :checkout, :checkin,
:clear_reloadable_connections!, :verify_active_connections!,
:connected?, :disconnect!, :with => :@connection_mutex
private
def active_connection_name #:nodoc:
Thread.current.object_id
end
# Remove stale threads from the cache.
def remove_stale_cached_threads!(cache, &block)
keys = Set.new(cache.keys)
Thread.list.each do |thread|
keys.delete(thread.object_id) if thread.alive?
end
keys.each do |key|
next unless cache.has_key?(key)
block.call(key, cache[key])
cache.delete(key)
end
end
end
class ConnectionPerThread < ConnectionPool
def active_connection
@reserved_connections[active_connection_name]
end
def active_connections; @reserved_connections; end
def checkout
new_connection
end
def checkin(conn)
conn.disconnect!
end
private
# Set the connection for the class.
def new_connection
config = spec.config.reverse_merge(:allow_concurrency => ActiveRecord::Base.allow_concurrency)
ActiveRecord::Base.send(spec.adapter_method, config)
end
def connections
@reserved_connections.values
end
def remove_connection(conn)
@reserved_connections.delete_if {|k,v| v == conn}
end
end
module ConnectionHandlerMethods
def initialize(pools = {})
@connection_pools = pools
end
def connection_pools
@connection_pools ||= {}
end
def establish_connection(name, spec)
@connection_pools[name] = ConnectionAdapters::ConnectionPool.create(spec)
end
# for internal use only and for testing;
# only works with ConnectionPerThread pool class
def active_connections #:nodoc:
@connection_pools.inject({}) do |hash,kv|
hash[kv.first] = kv.last.active_connection
hash.delete(kv.first) unless hash[kv.first]
hash
end
end
# Clears the cache which maps classes to connections.
def clear_active_connections!
@connection_pools.each_value {|pool| pool.release_thread_connection }
end
# Clears the cache which maps classes
def clear_reloadable_connections!
@connection_pools.each_value {|pool| pool.clear_reloadable_connections! }
end
def clear_all_connections!
@connection_pools.each_value {|pool| pool.disconnect! }
end
# Verify active connections.
def verify_active_connections! #:nodoc:
@connection_pools.each_value {|pool| pool.verify_active_connections!}
end
# 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).
def retrieve_connection(klass) #:nodoc:
pool = retrieve_connection_pool(klass)
(pool && pool.connection) or raise ConnectionNotEstablished
end
# Returns true if a connection that's accessible to this class has
# already been opened.
def connected?(klass)
retrieve_connection_pool(klass).connected?
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.
def remove_connection(klass)
pool = @connection_pools[klass.name]
@connection_pools.delete_if { |key, value| value == pool }
pool.disconnect! if pool
pool.spec.config if pool
end
private
def retrieve_connection_pool(klass)
loop do
pool = @connection_pools[klass.name]
return pool if pool
return nil if ActiveRecord::Base == klass
klass = klass.superclass
end
end
end
# This connection handler is not thread-safe, as it does not protect access
# to the underlying connection pools.
class SingleThreadConnectionHandler
include ConnectionHandlerMethods
end
# This connection handler is thread-safe. Each access or modification of a thread
# pool is synchronized by an internal monitor.
class MultipleThreadConnectionHandler
attr_reader :connection_pools_lock
include ConnectionHandlerMethods
def initialize(pools = {})
super
@connection_pools_lock = Monitor.new
end
# Apply monitor to all public methods that access the pool.
synchronize :establish_connection, :retrieve_connection,
:connected?, :remove_connection, :active_connections,
:clear_active_connections!, :clear_reloadable_connections!,
:clear_all_connections!, :verify_active_connections!,
:with => :connection_pools_lock
end
end
end
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