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

allocated[R]

A hash with thread keys and connection values for currently allocated connections.

available_connections[R]

An array of connections that are available for use by the pool.

max_size[R]

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

Public Class Methods

new(db, opts = OPTS) click to toggle source

The following additional options are respected:

  • :connection_handling - Set how to handle available connections. By default, uses a a queue for fairness. Can be set to :stack to use a stack, which may offer better performance.

  • :max_connections - The maximum number of connections the connection pool will open (default 4)

  • :pool_sleep_time - The amount of time to sleep before attempting to acquire a connection again, only used on ruby 1.8. (default 0.001)

  • :pool_timeout - The amount of seconds to wait to acquire a connection before raising a PoolTimeoutError (default 5)

Calls superclass method Sequel::ConnectionPool.new
# File lib/sequel/connection_pool/threaded.rb, line 34
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)

  if USE_WAITER
    @waiter = ConditionVariable.new
  else
    # :nocov:
    @sleep_time = Float(opts[:pool_sleep_time] || 0.001)
    # :nocov:
  end
end

Public Instance Methods

all_connections() { |c| ... } 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. 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 58
def all_connections
  hold do |c|
    sync do
      yield c
      @available_connections.each{|conn| yield conn}
    end
  end
end
disconnect(opts=OPTS) click to toggle source

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 77
def disconnect(opts=OPTS)
  conns = nil
  sync do
    conns = @available_connections.dup
    @available_connections.clear
  end
  conns.each{|conn| disconnect_connection(conn)}
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/threaded.rb, line 100
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
      @allocated.delete(t)
    end
    raise
  ensure
    sync{release(t)} if conn
  end
end
pool_type() click to toggle source
# File lib/sequel/connection_pool/threaded.rb, line 121
def pool_type
  :threaded
end
size() click to toggle source

The total number of connections opened, either available or allocated. This may not be completely accurate as it isn't protected by the mutex.

# File lib/sequel/connection_pool/threaded.rb, line 127
def size
  @allocated.length + @available_connections.length
end

Private Instance Methods

_acquire(thread) click to toggle source

Assigns a connection to the supplied thread, if one is available. The calling code should already have the mutex when calling this.

# File lib/sequel/connection_pool/threaded.rb, line 136
def _acquire(thread)
  if conn = available
    @allocated[thread] = conn
  end
end
acquire(thread) click to toggle source

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 149
def acquire(thread)
  sync do
    if conn = _acquire(thread)
      return conn
    end

    time = Time.now
    @waiter.wait(@mutex, @timeout)

    # Not sure why this is helpful, but calling Thread.pass after conditional
    # variable access dramatically increases reliability when under heavy
    # resource contention (almost eliminating timeouts), at a small cost to
    # runtime performance.
    Thread.pass

    until conn = _acquire(thread)
      deadline ||= time + @timeout
      current_time = Time.now
      raise_pool_timeout(current_time - time) if current_time > deadline
      # :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
      @waiter.wait(@mutex, deadline - current_time)
      Thread.pass
      # :nocov:
    end

    conn
  end
end
available() click to toggle source

Returns an available connection. If no connection is available, tries to create a new connection. The calling code should already have the mutex before calling this.

# File lib/sequel/connection_pool/threaded.rb, line 200
def available
  next_available || make_new(DEFAULT_SERVER)
end
checkin_connection(conn) click to toggle source

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 206
def checkin_connection(conn)
  @available_connections << conn
  if USE_WAITER
    @waiter.signal
    Thread.pass
  end
  conn
end
default_make_new(server)

Alias the default #make_new method, so subclasses can call it directly.

Alias for: make_new
make_new(server) click to toggle source

Creates a new connection to the given server if the size of the pool for the server is less than the maximum size of the pool. The calling code should already have the mutex before calling this.

Calls superclass method Sequel::ConnectionPool#make_new
# File lib/sequel/connection_pool/threaded.rb, line 223
def make_new(server)
  if (n = size) >= @max_size
    @allocated.keys.each{|t| release(t) unless t.alive?}
    n = nil
  end
  super if (n || size) < @max_size
end
Also aliased as: default_make_new
next_available() click to toggle source

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 234
def next_available
  case @connection_handling
  when :stack
    @available_connections.pop
  else
    @available_connections.shift
  end
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/threaded.rb, line 245
def owned_connection(thread)
  sync{@allocated[thread]}
end
preconnect(concurrent = false) click to toggle source

Create the maximum number of connections immediately.

# File lib/sequel/connection_pool/threaded.rb, line 250
def preconnect(concurrent = false)
  enum = (max_size - size).times

  if concurrent
    enum.map{Thread.new{make_new(nil)}}.map(&:join).each{|t| checkin_connection(t.value)}
  else
    enum.each{checkin_connection(make_new(nil))}
  end
end
raise_pool_timeout(elapsed) click to toggle source

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 262
def raise_pool_timeout(elapsed)
  name = db.opts[:name]
  raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}#{", database name: #{name}" if name}"
end
release(thread) click to toggle source

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 269
def release(thread)
  conn = @allocated.delete(thread)

  if @connection_handling == :disconnect
    disconnect_connection(conn)
  else
    checkin_connection(conn)
  end
end
sync() { || ... } click to toggle source

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 281
def sync
  @mutex.synchronize{yield}
end