class Sequel::ThreadedConnectionPool
A connection pool allowing multi-threaded access to a pool of connections. This is the default connection pool used by Sequel.
Constants
- USE_WAITER
Attributes
A hash with thread keys and connection values for currently allocated connections.
An array of connections that are available for use by the pool.
The maximum number of connections this pool will create (per shard/server if sharding).
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 PoolTimeoutError (default 5)
# File lib/sequel/connection_pool/threaded.rb, line 24 def initialize(db, opts = OPTS) super @max_size = Integer(opts[:max_connections] || 4) raise(Sequel::Error, ':max_connections must be positive') if @max_size < 1 @mutex = Mutex.new @connection_handling = opts[:connection_handling] @available_connections = [] @allocated = {} @timeout = Float(opts[:pool_timeout] || 5) @waiter = ConditionVariable.new 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. 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.
# File lib/sequel/connection_pool/threaded.rb, line 41 def all_connections hold do |c| sync do yield c @available_connections.each{|conn| yield conn} end end end
Removes all connections currently available, optionally yielding each
connection to the given block. 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.
# File lib/sequel/connection_pool/threaded.rb, line 60 def disconnect(opts=OPTS) conns = nil sync do conns = @available_connections.dup @available_connections.clear @waiter.signal end conns.each{|conn| disconnect_connection(conn)} 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/threaded.rb, line 83 def hold(server=nil) t = Thread.current if conn = owned_connection(t) return yield(conn) end begin conn = acquire(t) yield conn rescue Sequel::DatabaseDisconnectError, *@error_classes => e if disconnect_error?(e) oconn = conn conn = nil disconnect_connection(oconn) if oconn sync do @allocated.delete(t) @waiter.signal end end raise ensure sync{release(t)} if conn end end
# File lib/sequel/connection_pool/threaded.rb, line 107 def pool_type :threaded end
The total number of connections opened, either available or allocated. The calling code should not have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 113 def size @mutex.synchronize{_size} end
Private Instance Methods
The total number of connections opened, either available or allocated. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 121 def _size @allocated.length + @available_connections.length 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 nil if a connection could not be acquired within the timeout.
# File lib/sequel/connection_pool/threaded.rb, line 131 def acquire(thread) if conn = assign_connection(thread) return conn end timeout = @timeout timer = Sequel.start_timer sync do @waiter.wait(@mutex, timeout) if conn = next_available return(@allocated[thread] = conn) end end until conn = assign_connection(thread) elapsed = Sequel.elapsed_seconds_since(timer) raise_pool_timeout(elapsed) if elapsed > timeout # :nocov: # It's difficult to get to this point, it can only happen if there is a race condition # where a connection cannot be acquired even after the thread is signalled by the condition sync do @waiter.wait(@mutex, timeout - elapsed) if conn = next_available return(@allocated[thread] = conn) end end # :nocov: end conn 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.
# File lib/sequel/connection_pool/threaded.rb, line 167 def assign_connection(thread) allocated = @allocated do_make_new = false sync do if conn = next_available return(allocated[thread] = conn) end if (n = _size) >= (max = @max_size) allocated.keys.each{|t| release(t) unless t.alive?} n = nil end if (n || _size) < max do_make_new = allocated[thread] = true end end # Connect to the database outside of the connection pool mutex, # as that can take a long time and the connection pool mutex # shouldn't be locked while the connection takes place. if do_make_new begin conn = make_new(:default) sync{allocated[thread] = conn} ensure unless conn sync{allocated.delete(thread)} end end end conn end
Return a connection to the pool of available connections, returns the connection. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 205 def checkin_connection(conn) @available_connections << conn conn 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.
# File lib/sequel/connection_pool/threaded.rb, line 213 def next_available case @connection_handling when :stack @available_connections.pop else @available_connections.shift end 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/threaded.rb, line 224 def owned_connection(thread) sync{@allocated[thread]} end
Create the maximum number of connections immediately. The calling code should NOT have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 230 def preconnect(concurrent = false) enum = (max_size - _size).times conns = if concurrent enum.map{Thread.new{make_new(:default)}}.map(&:value) else enum.map{make_new(:default)} end sync{conns.each{|conn| checkin_connection(conn)}} end
Raise a PoolTimeout error showing the current timeout, the elapsed time, and the database's name (if any).
# File lib/sequel/connection_pool/threaded.rb, line 244 def raise_pool_timeout(elapsed) name = db.opts[:name] raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}#{", database name: #{name}" if name}" end
Releases the connection assigned to the supplied thread back to the pool. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 251 def release(thread) conn = @allocated.delete(thread) if @connection_handling == :disconnect disconnect_connection(conn) else checkin_connection(conn) end @waiter.signal nil end
Yield to the block while inside the mutex. The calling code should NOT already have the mutex before calling this.
# File lib/sequel/connection_pool/threaded.rb, line 266 def sync @mutex.synchronize{yield} end