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)
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
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
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
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
The number of threads waiting to check out a connection.
# File lib/sequel/connection_pool/timed_queue.rb 106 def num_waiting(_server=:default) 107 @queue.num_waiting 108 end
# File lib/sequel/connection_pool/timed_queue.rb 110 def pool_type 111 :timed_queue 112 end
The total number of connections in the pool.
# File lib/sequel/connection_pool/timed_queue.rb 115 def size 116 sync{@size[0]} 117 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 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
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 176 def can_make_new?(current_size) 177 if @max_size > current_size 178 @size[0] += 1 179 end 180 end
Adds a connection to the queue of available connections, returns the connection.
# File lib/sequel/connection_pool/timed_queue.rb 264 def checkin_connection(conn) 265 @queue.push(conn) 266 conn 267 end
Decrement the current size of the pool when disconnecting connections.
Calling code should not have the mutex when calling this.
Sequel::ConnectionPool#disconnect_connection
# File lib/sequel/connection_pool/timed_queue.rb 143 def disconnect_connection(conn) 144 sync{@size[0] -= 1} 145 super 146 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 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
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 233 def owned_connection(thread) 234 sync{@allocated[thread]} 235 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 133 def preallocated_make_new 134 make_new(:default) 135 rescue Exception 136 sync{@size[0] -= 1} 137 raise 138 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 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
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 258 def release(thread) 259 checkin_connection(sync{@allocated.delete(thread)}) 260 nil 261 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 272 def sync 273 @mutex.synchronize{yield} 274 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 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