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 = available) && !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   nconns = 0
63   while conn = available
64     nconns += 1
65     disconnect_connection(conn)
66   end
67   fill_queue(nconns)
68   nil
69 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
 84 def hold(server=nil)
 85   t = Sequel.current
 86   if conn = owned_connection(t)
 87     return yield(conn)
 88   end
 89 
 90   begin
 91     conn = acquire(t)
 92     yield conn
 93   rescue Sequel::DatabaseDisconnectError, *@error_classes => e
 94     if disconnect_error?(e)
 95       oconn = conn
 96       conn = nil
 97       disconnect_connection(oconn) if oconn
 98       sync{@allocated.delete(t)}
 99       fill_queue(1)
100     end
101     raise
102   ensure
103     release(t) if conn
104   end
105 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
108 def num_waiting(_server=:default)
109   @queue.num_waiting
110 end

The number of threads waiting to check out a connection.

pool_type ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
112 def pool_type
113   :timed_queue
114 end

size ()

Source

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

The total number of connections in the pool.

Private Instance Methods

acquire (thread)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
227 def acquire(thread)
228   if conn = available || try_make_new || wait_until_available
229     sync{@allocated[thread] = conn}
230   else
231     name = db.opts[:name]
232     raise ::Sequel::PoolTimeout, "timeout: #{@timeout}#{", database name: #{name}" if name}"
233   end
234 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.

available ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
238 def available
239   @queue.pop(timeout: 0)
240 end

Return the next connection in the pool if there is one available. Returns nil if no connection is currently available.

can_make_new? (current_size)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
181 def can_make_new?(current_size)
182   if @max_size > current_size
183     @size[0] += 1
184   end
185 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
282 def checkin_connection(conn)
283   @queue.push(conn)
284   conn
285 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
145 def disconnect_connection(conn)
146   sync{@size[0] -= 1}
147   super
148 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 (nconns)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
164 def fill_queue(nconns)
165   if nconns > 0 && @queue.num_waiting > 0
166     Thread.new do
167       while nconns > 0 && @queue.num_waiting > 0 && (conn = try_make_new)
168         @queue.push(conn)
169       end
170     end
171   end
172 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.

nconns specifies the maximum number of connections to add, which should be the number of connections that were disconnected.

owned_connection (thread)

Source

    # File lib/sequel/connection_pool/timed_queue.rb
251 def owned_connection(thread)
252   sync{@allocated[thread]}
253 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
135 def preallocated_make_new
136   make_new(:default)
137 rescue Exception
138   sync{@size[0] -= 1}
139   raise
140 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
259 def preconnect(concurrent = false)
260   if concurrent
261     if times = sync{@max_size > (size = @size[0]) ? @max_size - size : false}
262       Array.new(times){Thread.new{if conn = try_make_new; @queue.push(conn) end}}.map(&:value)
263     end
264   else
265     while conn = try_make_new
266       @queue.push(conn)
267     end
268   end
269 
270   nil
271 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
276 def release(thread)
277   checkin_connection(sync{@allocated.delete(thread)})
278   nil
279 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
290 def sync
291   @mutex.synchronize{yield}
292 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
192 def try_make_new
193   return preallocated_make_new if sync{can_make_new?(@size[0])}
194 
195   to_disconnect = nil
196   do_make_new = false
197 
198   sync do
199     current_size = @size[0]
200     @allocated.keys.each do |t|
201       unless t.alive?
202         (to_disconnect ||= []) << @allocated.delete(t)
203         current_size -= 1
204       end
205     end
206   
207     do_make_new = true if can_make_new?(current_size)
208   end
209 
210   begin
211     preallocated_make_new if do_make_new
212   ensure
213     if to_disconnect
214       to_disconnect.each{|conn| disconnect_connection(conn)}
215       fill_queue(to_disconnect.size)
216     end
217   end
218 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.

wait_until_available ()

Source

    # File lib/sequel/connection_pool/timed_queue.rb
245 def wait_until_available
246   @queue.pop(timeout: @timeout)
247 end

Return the next connection in the pool if there is one available. If not, wait until the timeout for a connection to become available. If there is still no available connection, return nil.