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
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

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
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
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
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
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
 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
pool_type() click to toggle source
    # File lib/sequel/connection_pool/timed_queue.rb
105 def pool_type
106   :timed_queue
107 end
size() click to toggle source

The total number of connections in the pool.

    # File lib/sequel/connection_pool/timed_queue.rb
110 def size
111   sync{@size[0]}
112 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
217 def acquire(thread)
218   if conn = @queue.pop(timeout: 0) || try_make_new || @queue.pop(timeout: @timeout)
219     sync{@allocated[thread] = conn}
220   else
221     name = db.opts[:name]
222     raise ::Sequel::PoolTimeout, "timeout: #{@timeout}#{", database name: #{name}" if name}"
223   end
224 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
171 def can_make_new?(current_size)
172   if @max_size > current_size
173     @size[0] += 1
174   end
175 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
259 def checkin_connection(conn)
260   @queue.push(conn)
261   conn
262 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
138 def disconnect_connection(conn)
139   sync{@size[0] -= 1}
140   super
141 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
154 def fill_queue
155   if @queue.num_waiting > 0
156     Thread.new do
157       while @queue.num_waiting > 0 && (conn = try_make_new)
158         @queue.push(conn)
159       end
160     end
161   end
162 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
228 def owned_connection(thread)
229   sync{@allocated[thread]}
230 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
128 def preallocated_make_new
129   make_new(:default)
130 rescue Exception
131   sync{@size[0] -= 1}
132   raise
133 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
236 def preconnect(concurrent = false)
237   if concurrent
238     if times = sync{@max_size > (size = @size[0]) ? @max_size - size : false}
239       times.times.map{Thread.new{if conn = try_make_new; @queue.push(conn) end}}.map(&:value)
240     end
241   else
242     while conn = try_make_new
243       @queue.push(conn)
244     end
245   end
246 
247   nil
248 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
253 def release(thread)
254   checkin_connection(sync{@allocated.delete(thread)})
255   nil
256 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
267 def sync
268   @mutex.synchronize{yield}
269 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
182 def try_make_new
183   return preallocated_make_new if sync{can_make_new?(@size[0])}
184 
185   to_disconnect = nil
186   do_make_new = false
187 
188   sync do
189     current_size = @size[0]
190     @allocated.keys.each do |t|
191       unless t.alive?
192         (to_disconnect ||= []) << @allocated.delete(t)
193         current_size -= 1
194       end
195     end
196   
197     do_make_new = true if can_make_new?(current_size)
198   end
199 
200   begin
201     preallocated_make_new if do_make_new
202   ensure
203     if to_disconnect
204       to_disconnect.each{|conn| disconnect_connection(conn)}
205       fill_queue
206     end
207   end
208 end