class Sequel::TimedQueueConnectionPool
A connection pool allowing multi-threaded access to a pool of connections, using a timed queue (only available in Ruby 3.2+).
Attributes
The maximum number of connections this pool will create.
Public Class Methods
The following additional options are respected:
- :max_connections
-
The maximum number of connections the connection pool will open (default 4)
- :pool_timeout
-
The amount of seconds to wait to acquire a connection before raising a PoolTimeout (default 5)
# File lib/sequel/connection_pool/timed_queue.rb, line 17 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 # Size inside array so this still works while the pool is frozen. @size = [0] @allocated = {} @allocated.compare_by_identity @timeout = Float(opts[:pool_timeout] || 5) @queue = Queue.new 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.
# File lib/sequel/connection_pool/timed_queue.rb, line 33 def all_connections hold do |conn| yield conn # Use a hash to record all connections already seen. As soon as we # come across a connection we've already seen, we stop the loop. conns = {} conns.compare_by_identity while true conn = nil begin break unless (conn = @queue.pop(timeout: 0)) && !conns[conn] conns[conn] = true yield conn ensure @queue.push(conn) if conn end end end end
Removes all connections currently in the pool's queue. This method has the effect of disconnecting from the database, assuming that no connections are currently being used.
Once a connection is requested using hold, the connection pool creates new connections to the database.
# File lib/sequel/connection_pool/timed_queue.rb, line 60 def disconnect(opts=OPTS) while conn = @queue.pop(timeout: 0) disconnect_connection(conn) end fill_queue nil 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/timed_queue.rb, line 81 def hold(server=nil) t = Sequel.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 sync{@allocated.delete(t)} fill_queue end raise ensure release(t) if conn end end
# File lib/sequel/connection_pool/timed_queue.rb, line 104 def pool_type :timed_queue end
The total number of connections in the pool.
# File lib/sequel/connection_pool/timed_queue.rb, line 109 def size sync{@size[0]} end
Private Instance Methods
Assigns a connection to the supplied thread, if one is available.
This should return a connection is one is available within the timeout, or raise PoolTimeout if a connection could not be acquired within the timeout.
Calling code should not have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 216 def acquire(thread) if conn = @queue.pop(timeout: 0) || try_make_new || @queue.pop(timeout: @timeout) sync{@allocated[thread] = conn} else name = db.opts[:name] raise ::Sequel::PoolTimeout, "timeout: #{@timeout}#{", database name: #{name}" if name}" end end
Whether the given size is less than the maximum size of the pool. In that case, the pool's current size is incremented. If this method returns true, space in the pool for the connection is preallocated, and #preallocated_make_new should be called to create the connection.
Calling code should have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 170 def can_make_new?(current_size) if @max_size > current_size @size[0] += 1 end end
Adds a connection to the queue of available connections, returns the connection.
# File lib/sequel/connection_pool/timed_queue.rb, line 258 def checkin_connection(conn) @queue.push(conn) conn end
Decrement the current size of the pool when disconnecting connections.
Calling code should not have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 137 def disconnect_connection(conn) sync{@size[0] -= 1} super end
If there are any threads waiting on the queue, try to create new connections in a separate thread if the pool is not yet at the maximum size.
The reason for this method is to handle cases where acquire could not retrieve a connection immediately, and the pool was already at the maximum size. In that case, the acquire will wait on the queue until the timeout. This method is called after disconnecting to potentially add new connections to the pool, so the threads that are currently waiting for connections do not timeout after the pool is no longer full.
# File lib/sequel/connection_pool/timed_queue.rb, line 153 def fill_queue if @queue.num_waiting > 0 Thread.new do while @queue.num_waiting > 0 && (conn = try_make_new) @queue.push(conn) end end 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/timed_queue.rb, line 227 def owned_connection(thread) sync{@allocated[thread]} end
Create a new connection, after the pool's current size has already been updated to account for the new connection. If there is an exception when creating the connection, decrement the current size.
This should only be called after can_make_new?. If there is an exception between when can_make_new? is called and when #preallocated_make_new is called, it has the effect of reducing the maximum size of the connection pool by 1, since the current size of the pool will show a higher number than the number of connections allocated or in the queue.
Calling code should not have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 127 def preallocated_make_new make_new(:default) rescue Exception sync{@size[0] -= 1} raise end
Create the maximum number of connections immediately. This should not be called with a true argument unless no code is currently operating on the database.
Calling code should not have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 235 def preconnect(concurrent = false) if concurrent if times = sync{@max_size > (size = @size[0]) ? @max_size - size : false} times.times.map{Thread.new{if conn = try_make_new; @queue.push(conn) end}}.map(&:value) end else while conn = try_make_new @queue.push(conn) end end nil end
Releases the connection assigned to the supplied thread back to the pool.
Calling code should not have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 252 def release(thread) checkin_connection(sync{@allocated.delete(thread)}) nil end
Yield to the block while inside the mutex.
Calling code should not have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 266 def sync @mutex.synchronize{yield} end
Try to make a new connection if there is space in the pool. If the pool is already full, look for dead threads/fibers and disconnect the related connections.
Calling code should not have the mutex when calling this.
# File lib/sequel/connection_pool/timed_queue.rb, line 181 def try_make_new return preallocated_make_new if sync{can_make_new?(@size[0])} to_disconnect = nil do_make_new = false sync do current_size = @size[0] @allocated.keys.each do |t| unless t.alive? (to_disconnect ||= []) << @allocated.delete(t) current_size -= 1 end end do_make_new = true if can_make_new?(current_size) end begin preallocated_make_new if do_make_new ensure if to_disconnect to_disconnect.each{|conn| disconnect_connection(conn)} fill_queue end end end