class Sequel::ThreadedConnectionPool

A connection pool allowing multi-threaded access to a pool of connections. This is the default connection pool used by Sequel.

Attributes

allocated [R]

A hash with thread/fiber keys and connection values for currently allocated connections. The calling code should already have the mutex before calling this.

available_connections [R]

An array of connections that are available for use by the pool. The calling code should already have the mutex before calling this.

max_size [R]

The maximum number of connections this pool will create (per shard/server if sharding).

Public Class Methods

new (db, opts = OPTS)

Source

   # File lib/sequel/connection_pool/threaded.rb
28 def initialize(db, opts = OPTS)
29   super
30   @max_size = Integer(opts[:max_connections] || 4)
31   raise(Sequel::Error, ':max_connections must be positive') if @max_size < 1
32   @mutex = Mutex.new  
33   @connection_handling = opts[:connection_handling]
34   @available_connections = []
35   @allocated = {}
36   @allocated.compare_by_identity
37   @timeout = Float(opts[:pool_timeout] || 5)
38   @waiter = ConditionVariable.new
39 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 error (default 5)

Calls superclass method Sequel::ConnectionPool::new

Public Instance Methods

all_connections () { |c| ... }

Source

   # File lib/sequel/connection_pool/threaded.rb
46 def all_connections
47   hold do |c|
48     sync do
49       yield c
50       @available_connections.each{|conn| yield conn}
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. This holds the mutex while it is yielding all of the available connections, which means that until the method’s block returns, the pool is locked.

disconnect (opts=OPTS)

Source

   # File lib/sequel/connection_pool/threaded.rb
64 def disconnect(opts=OPTS)
65   conns = nil
66   sync do
67     conns = @available_connections.dup
68     @available_connections.clear
69     @waiter.signal
70   end
71   conns.each{|conn| disconnect_connection(conn)}
72 end

Removes all connections currently available. This method has the effect of disconnecting from the database, assuming that no connections are currently being used. If you want to be able to disconnect connections that are currently in use, use the ShardedThreadedConnectionPool, which can do that. This connection pool does not, for performance reasons. To use the sharded pool, pass the servers: {} option when connecting to the database.

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/threaded.rb
 87 def hold(server=nil)
 88   t = Sequel.current
 89   if conn = owned_connection(t)
 90     return yield(conn)
 91   end
 92   begin
 93     conn = acquire(t)
 94     yield conn
 95   rescue Sequel::DatabaseDisconnectError, *@error_classes => e
 96     if disconnect_error?(e)
 97       oconn = conn
 98       conn = nil
 99       disconnect_connection(oconn) if oconn
100       sync do 
101         @allocated.delete(t)
102         @waiter.signal
103       end
104     end
105     raise
106   ensure
107     if conn
108       sync{release(t)}
109       if @connection_handling == :disconnect
110         disconnect_connection(conn)
111       end
112     end
113   end
114 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.

pool_type ()

Source

    # File lib/sequel/connection_pool/threaded.rb
116 def pool_type
117   :threaded
118 end

size ()

Source

    # File lib/sequel/connection_pool/threaded.rb
122 def size
123   @mutex.synchronize{_size}
124 end

The total number of connections opened, either available or allocated. The calling code should not have the mutex before calling this.

Private Instance Methods

_size ()

Source

    # File lib/sequel/connection_pool/threaded.rb
130 def _size
131   @allocated.length + @available_connections.length
132 end

The total number of connections opened, either available or allocated. The calling code should already have the mutex before calling this.

acquire (thread)

Source

    # File lib/sequel/connection_pool/threaded.rb
140 def acquire(thread)
141   if conn = assign_connection(thread)
142     return conn
143   end
144 
145   timeout = @timeout
146   timer = Sequel.start_timer
147 
148   if conn = acquire_available(thread, timeout)
149     return conn
150   end
151 
152   until conn = assign_connection(thread)
153     elapsed = Sequel.elapsed_seconds_since(timer)
154     # simplecov:disable
155     raise_pool_timeout(elapsed) if elapsed > timeout
156 
157     # It's difficult to get to this point, it can only happen if there is a race condition
158     # where a connection cannot be acquired even after the thread is signalled by the condition variable
159     if conn = acquire_available(thread, timeout - elapsed)
160       return conn
161     end
162     # simplecov:enable
163   end
164 
165   conn
166 end

Assigns a connection to the supplied thread, if one is available. The calling code should NOT already have the mutex when calling this.

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.

acquire_available (thread, timeout)

Source

    # File lib/sequel/connection_pool/threaded.rb
169 def acquire_available(thread, timeout)
170   sync do
171     # Check if connection was checked in between when assign_connection failed and now.
172     # This is very unlikely, but necessary to prevent a situation where the waiter
173     # will wait for a connection even though one has already been checked in.
174     # simplecov:disable
175     if conn = next_available
176       return(@allocated[thread] = conn)
177     end
178     # simplecov:enable
179 
180     @waiter.wait(@mutex, timeout)
181 
182     # Connection still not available, could be because a connection was disconnected,
183     # may have to retry assign_connection to see if a new connection can be made.
184     if conn = next_available
185       return(@allocated[thread] = conn)
186     end
187   end
188 end

Acquire a connection if one is already available, or waiting until it becomes available.

assign_connection (thread)

Source

    # File lib/sequel/connection_pool/threaded.rb
192 def assign_connection(thread)
193   # Thread safe as instance variable is only assigned to local variable
194   # and not operated on outside mutex.
195   allocated = @allocated
196   do_make_new = false
197   to_disconnect = nil
198 
199   sync do
200     if conn = next_available
201       return(allocated[thread] = conn)
202     end
203 
204     if (n = _size) >= (max = @max_size)
205       allocated.keys.each do |t|
206         unless t.alive?
207           (to_disconnect ||= []) << allocated.delete(t)
208         end
209       end
210       n = nil
211     end
212 
213     if (n || _size) < max
214       do_make_new = allocated[thread] = true
215     end
216   end
217 
218   if to_disconnect
219     to_disconnect.each{|dconn| disconnect_connection(dconn)}
220   end
221 
222   # Connect to the database outside of the connection pool mutex,
223   # as that can take a long time and the connection pool mutex
224   # shouldn't be locked while the connection takes place.
225   if do_make_new
226     begin
227       conn = make_new(:default)
228       sync{allocated[thread] = conn}
229     ensure
230       unless conn
231         sync{allocated.delete(thread)}
232       end
233     end
234   end
235 
236   conn
237 end

Assign a connection to the thread, or return nil if one cannot be assigned. The caller should NOT have the mutex before calling this.

checkin_connection (conn)

Source

    # File lib/sequel/connection_pool/threaded.rb
241 def checkin_connection(conn)
242   @available_connections << conn
243   conn
244 end

Return a connection to the pool of available connections, returns the connection. The calling code should already have the mutex before calling this.

next_available ()

Source

    # File lib/sequel/connection_pool/threaded.rb
249 def next_available
250   case @connection_handling
251   when :stack
252     @available_connections.pop
253   else
254     @available_connections.shift
255   end
256 end

Return the next available connection in the pool, or nil if there is not currently an available connection. The calling code should already have the mutex before calling this.

owned_connection (thread)

Source

    # File lib/sequel/connection_pool/threaded.rb
260 def owned_connection(thread)
261   sync{@allocated[thread]}
262 end

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

preconnect (concurrent = false)

Source

    # File lib/sequel/connection_pool/threaded.rb
266 def preconnect(concurrent = false)
267   enum = (max_size - _size).times
268 
269   conns = if concurrent
270     enum.map{Thread.new{make_new(:default)}}.map(&:value)
271   else
272     enum.map{make_new(:default)}
273   end
274 
275   sync{conns.each{|conn| checkin_connection(conn)}}
276 end

Create the maximum number of connections immediately. The calling code should NOT have the mutex before calling this.

raise_pool_timeout (elapsed)

Source

    # File lib/sequel/connection_pool/threaded.rb
280 def raise_pool_timeout(elapsed)
281   name = db.opts[:name]
282   raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}#{", database name: #{name}" if name}"
283 end

Raise a PoolTimeout error showing the current timeout, the elapsed time, and the database’s name (if any).

release (thread)

Source

    # File lib/sequel/connection_pool/threaded.rb
287 def release(thread)
288   conn = @allocated.delete(thread)
289 
290   unless @connection_handling == :disconnect
291     checkin_connection(conn)
292   end
293 
294   @waiter.signal
295   
296   # Ensure that after signalling the condition, some other thread is given the
297   # opportunity to acquire the mutex.
298   # See <https://github.com/socketry/async/issues/99> for more context.
299   sleep(0)
300   
301   nil
302 end

Releases the connection assigned to the supplied thread back to the pool. The calling code should already have the mutex before calling this.

sync () { || ... }

Source

    # File lib/sequel/connection_pool/threaded.rb
306 def sync
307   @mutex.synchronize{yield}
308 end

Yield to the block while inside the mutex. The calling code should NOT already have the mutex before calling this.