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)

Source

   # File lib/sequel/connection_pool/timed_queue.rb
18 def initialize(db, opts = OPTS)
19   super
20   @max_size = Integer(opts[:max_connections] || 4)
21   raise(Sequel::Error, ':max_connections must be positive') if @max_size < 1
22   @mutex = Mutex.new  
23   # Size inside array so this still works while the pool is frozen.
24   @size = [0]
25   @allocated = {}
26   @allocated.compare_by_identity
27   @timeout = Float(opts[:pool_timeout] || 5)
28   @queue = Queue.new
29 end

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

Public Instance Methods

all_connections () { |conn| ... }

Source

   # File lib/sequel/connection_pool/timed_queue.rb
34 def all_connections
35   hold do |conn|
36     yield conn
37 
38     # Use a hash to record all connections already seen.  As soon as we
39     # come across a connection we've already seen, we stop the loop.
40     conns = {}
41     conns.compare_by_identity
42     while true
43       conn = nil
44       begin
45         break unless (conn = @queue.pop(timeout: 0)) && !conns[conn]
46         conns[conn] = true
47         yield conn
48       ensure
49         @queue.push(conn) if conn
50       end
51     end
52   end
53 end

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.

disconnect (opts=OPTS)

Source

   # File lib/sequel/connection_pool/timed_queue.rb
61 def disconnect(opts=OPTS)
62   while conn = @queue.pop(timeout: 0)
63     disconnect_connection(conn)
64   end
65   fill_queue
66   nil
67 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.

hold (server=nil) { |conn| ... }

Source

    # File lib/sequel/connection_pool/timed_queue.rb
 82 def hold(server=nil)
 83   t = Sequel.current
 84   if conn = owned_connection(t)
 85     return yield(conn)
 86   end
 87 
 88   begin
 89     conn = acquire(t)
 90     yield conn
 91   rescue Sequel::DatabaseDisconnectError, *@error_classes => e
 92     if disconnect_error?(e)
 93       oconn = conn
 94       conn = nil
 95       disconnect_connection(oconn) if oconn
 96       sync{@allocated.delete(t)}
 97       fill_queue
 98     end
 99     raise
100   ensure
101     release(t) if conn
102   end
103 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.

num_waiting (_server=:default)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
106 def num_waiting(_server=:default)
107   @queue.num_waiting
108 end

The number of threads waiting to check out a connection.

pool_type ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
110 def pool_type
111   :timed_queue
112 end

size ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
115 def size
116   sync{@size[0]}
117 end

The total number of connections in the pool.

Private Instance Methods

acquire (thread)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
222 def acquire(thread)
223   if conn = @queue.pop(timeout: 0) || try_make_new || @queue.pop(timeout: @timeout)
224     sync{@allocated[thread] = conn}
225   else
226     name = db.opts[:name]
227     raise ::Sequel::PoolTimeout, "timeout: #{@timeout}#{", database name: #{name}" if name}"
228   end
229 end

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.

can_make_new? (current_size)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
176 def can_make_new?(current_size)
177   if @max_size > current_size
178     @size[0] += 1
179   end
180 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.

checkin_connection (conn)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
264 def checkin_connection(conn)
265   @queue.push(conn)
266   conn
267 end

Adds a connection to the queue of available connections, returns the connection.

disconnect_connection (conn)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
143 def disconnect_connection(conn)
144   sync{@size[0] -= 1}
145   super
146 end

Decrement the current size of the pool when disconnecting connections.

Calling code should not have the mutex when calling this.

Calls superclass method Sequel::ConnectionPool#disconnect_connection

fill_queue ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
159 def fill_queue
160   if @queue.num_waiting > 0
161     Thread.new do
162       while @queue.num_waiting > 0 && (conn = try_make_new)
163         @queue.push(conn)
164       end
165     end
166   end
167 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.

owned_connection (thread)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
233 def owned_connection(thread)
234   sync{@allocated[thread]}
235 end

Returns the connection owned by the supplied thread, if any. The calling code should NOT already have the mutex before calling this.

preallocated_make_new ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
133 def preallocated_make_new
134   make_new(:default)
135 rescue Exception
136   sync{@size[0] -= 1}
137   raise
138 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.

preconnect (concurrent = false)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
241 def preconnect(concurrent = false)
242   if concurrent
243     if times = sync{@max_size > (size = @size[0]) ? @max_size - size : false}
244       Array.new(times){Thread.new{if conn = try_make_new; @queue.push(conn) end}}.map(&:value)
245     end
246   else
247     while conn = try_make_new
248       @queue.push(conn)
249     end
250   end
251 
252   nil
253 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.

release (thread)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
258 def release(thread)
259   checkin_connection(sync{@allocated.delete(thread)})
260   nil
261 end

Releases the connection assigned to the supplied thread back to the pool.

Calling code should not have the mutex when calling this.

sync () { || ... }

Source

    # File lib/sequel/connection_pool/timed_queue.rb
272 def sync
273   @mutex.synchronize{yield}
274 end

Yield to the block while inside the mutex.

Calling code should not have the mutex when calling this.

try_make_new ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
187 def try_make_new
188   return preallocated_make_new if sync{can_make_new?(@size[0])}
189 
190   to_disconnect = nil
191   do_make_new = false
192 
193   sync do
194     current_size = @size[0]
195     @allocated.keys.each do |t|
196       unless t.alive?
197         (to_disconnect ||= []) << @allocated.delete(t)
198         current_size -= 1
199       end
200     end
201   
202     do_make_new = true if can_make_new?(current_size)
203   end
204 
205   begin
206     preallocated_make_new if do_make_new
207   ensure
208     if to_disconnect
209       to_disconnect.each{|conn| disconnect_connection(conn)}
210       fill_queue
211     end
212   end
213 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.