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

max_size[R]

The maximum number of connections this pool will create.

Public Class Methods

new(db, opts = OPTS) click to toggle source

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)

Calls superclass method Sequel::ConnectionPool.new
# 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

all_connections() { |conn| ... } click to toggle source

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
disconnect(opts=OPTS) click to toggle source

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
hold(server=nil) { |conn| ... } click to toggle source

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
pool_type() click to toggle source
# File lib/sequel/connection_pool/timed_queue.rb, line 104
def pool_type
  :timed_queue
end
size() click to toggle source

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

acquire(thread) click to toggle source

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
can_make_new?(current_size) click to toggle source

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
checkin_connection(conn) click to toggle source

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
disconnect_connection(conn) click to toggle source

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
fill_queue() click to toggle source

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
owned_connection(thread) click to toggle source

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
preallocated_make_new() click to toggle source

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
preconnect(concurrent = false) click to toggle source

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
release(thread) click to toggle source

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
sync() { || ... } click to toggle source

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_make_new() click to toggle source

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