class Sequel::ThreadedConnectionPool
A connection pool allowing multi-threaded access to a pool of connections. This is the default connection pool used by Sequel.
Constants
- USE_WAITER
Attributes
A hash with thread keys and connection values for currently allocated connections.
An array of connections that are available for use by the pool.
The maximum number of connections this pool will create (per shard/server if sharding).
Public Class Methods
The following additional options are respected:
-
:connection_handling - Set how to handle available connections. By default, uses a a queue for fairness. Can be set to :stack to use a stack, which may offer better performance.
-
:max_connections - The maximum number of connections the connection pool will open (default 4)
-
:pool_sleep_time - The amount of time to sleep before attempting to acquire a connection again, only used on ruby 1.8. (default 0.001)
-
:pool_timeout - The amount of seconds to wait to acquire a connection before raising a PoolTimeoutError (default 5)
# File lib/sequel/connection_pool/threaded.rb, line 34 def initialize(db, opts = OPTS) super @max_size = Integer(opts[:max_connections] || 4) raise(Sequel::Error, ':max_connections must be positive') if @max_size < 1 @mutex = Mutex.new @connection_handling = opts[:connection_handling] @available_connections = [] @allocated = {} @timeout = Float(opts[:pool_timeout] || 5) if USE_WAITER @waiter = ConditionVariable.new else # :nocov: @sleep_time = Float(opts[:pool_sleep_time] || 0.001) # :nocov: end end
Public Instance Methods
Yield all of the available connections, and the one currently allocated to this thread. This will not yield connections currently allocated to other threads, as it is not safe to operate on them. This holds the mutex while it is yielding all of the available connections, which means that until the method's block returns, the pool is locked.
# File lib/sequel/connection_pool/threaded.rb, line 58 def all_connections hold do |c| sync do yield c @available_connections.each{|conn| yield conn} end end end
Removes all connections currently available, optionally yielding each
connection to the given block. This method has the effect of disconnecting
from the database, assuming that no connections are currently being used.
If you want to be able to disconnect connections that are currently in use,
use the ShardedThreadedConnectionPool, which can do that. This connection
pool does not, for performance reasons. To use the sharded pool, pass the
:servers=>{}
option when connecting to the database.
Once a connection is requested using hold, the connection pool creates new connections to the database.
# File lib/sequel/connection_pool/threaded.rb, line 77 def disconnect(opts=OPTS) conns = nil sync do conns = @available_connections.dup @available_connections.clear end conns.each{|conn| disconnect_connection(conn)} end
Chooses the first available connection, or if none are available, creates a new connection. Passes the connection to the supplied block:
pool.hold {|conn| conn.execute('DROP TABLE posts')}
Pool#hold is re-entrant, meaning it can be called recursively in the same thread without blocking.
If no connection is immediately available and the pool is already using the maximum number of connections, Pool#hold will block until a connection is available or the timeout expires. If the timeout expires before a connection can be acquired, a Sequel::PoolTimeout is raised.
# File lib/sequel/connection_pool/threaded.rb, line 100 def hold(server=nil) t = Thread.current if conn = owned_connection(t) return yield(conn) end begin conn = acquire(t) yield conn rescue Sequel::DatabaseDisconnectError, *@error_classes => e if disconnect_error?(e) oconn = conn conn = nil disconnect_connection(oconn) if oconn @allocated.delete(t) end raise ensure sync{release(t)} if conn end end
# File lib/sequel/connection_pool/threaded.rb, line 121 def pool_type :threaded end
The total number of connections opened, either available or allocated. This may not be completely accurate as it isn't protected by the mutex.
# File lib/sequel/connection_pool/threaded.rb, line 127 def size @allocated.length + @available_connections.length end
Private Instance Methods
Assigns a connection to the supplied thread, if one is available. The calling code should already have the mutex when calling this.
# File lib/sequel/connection_pool/threaded.rb, line 136 def _acquire(thread) if conn = available @allocated[thread] = conn end end
Assigns a connection to the supplied thread, if one is available. The calling code should NOT already have the mutex when calling this.
This should return a connection is one is available within the timeout, or nil if a connection could not be acquired within the timeout.
# File lib/sequel/connection_pool/threaded.rb, line 149 def acquire(thread) sync do if conn = _acquire(thread) return conn end time = Time.now @waiter.wait(@mutex, @timeout) # Not sure why this is helpful, but calling Thread.pass after conditional # variable access dramatically increases reliability when under heavy # resource contention (almost eliminating timeouts), at a small cost to # runtime performance. Thread.pass until conn = _acquire(thread) deadline ||= time + @timeout current_time = Time.now raise_pool_timeout(current_time - time) if current_time > deadline # :nocov: # It's difficult to get to this point, it can only happen if there is a race condition # where a connection cannot be acquired even after the thread is signalled by the condition @waiter.wait(@mutex, deadline - current_time) Thread.pass # :nocov: end conn end end
Returns an available connection. If no connection is available, tries to create a new connection. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 200 def available next_available || make_new(DEFAULT_SERVER) end
Return a connection to the pool of available connections, returns the connection. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 206 def checkin_connection(conn) @available_connections << conn if USE_WAITER @waiter.signal Thread.pass end conn end
Alias the default #make_new method, so subclasses can call it directly.
Creates a new connection to the given server if the size of the pool for the server is less than the maximum size of the pool. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 223 def make_new(server) if (n = size) >= @max_size @allocated.keys.each{|t| release(t) unless t.alive?} n = nil end super if (n || size) < @max_size end
Return the next available connection in the pool, or nil if there is not currently an available connection. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 234 def next_available case @connection_handling when :stack @available_connections.pop else @available_connections.shift end end
Returns the connection owned by the supplied thread, if any. The calling code should NOT already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 245 def owned_connection(thread) sync{@allocated[thread]} end
Create the maximum number of connections immediately.
# File lib/sequel/connection_pool/threaded.rb, line 250 def preconnect(concurrent = false) enum = (max_size - size).times if concurrent enum.map{Thread.new{make_new(nil)}}.map(&:join).each{|t| checkin_connection(t.value)} else enum.each{checkin_connection(make_new(nil))} end end
Raise a PoolTimeout error showing the current timeout, the elapsed time, and the database's name (if any).
# File lib/sequel/connection_pool/threaded.rb, line 262 def raise_pool_timeout(elapsed) name = db.opts[:name] raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}#{", database name: #{name}" if name}" end
Releases the connection assigned to the supplied thread back to the pool. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 269 def release(thread) conn = @allocated.delete(thread) if @connection_handling == :disconnect disconnect_connection(conn) else checkin_connection(conn) end end
Yield to the block while inside the mutex. The calling code should NOT already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 281 def sync @mutex.synchronize{yield} end