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. 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) 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 PoolTimeoutError (default 5)

Calls superclass method Sequel::ConnectionPool.new
# File lib/sequel/connection_pool/threaded.rb, line 26
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

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 43
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 62
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
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 85
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
    if conn
      sync{release(t)}
      if @connection_handling == :disconnect
        disconnect_connection(conn)
      end
    end
  end
end
pool_type() click to toggle source
# File lib/sequel/connection_pool/threaded.rb, line 114
def pool_type
  :threaded
end
size() click to toggle source

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 120
def size
  @mutex.synchronize{_size}
end

Private Instance Methods

_size() click to toggle source

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 128
def _size
  @allocated.length + @available_connections.length
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 138
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 variable
    sync do
      @waiter.wait(@mutex, timeout - elapsed)
      if conn = next_available
        return(@allocated[thread] = conn)
      end
    end
    # :nocov:
  end

  conn
end
assign_connection(thread) click to toggle source

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 174
def assign_connection(thread)
  # Thread safe as instance variable is only assigned to local variable
  # and not operated on outside mutex.
  allocated = @allocated
  do_make_new = false
  to_disconnect = nil

  sync do
    if conn = next_available
      return(allocated[thread] = conn)
    end

    if (n = _size) >= (max = @max_size)
      allocated.keys.each do |t|
        unless t.alive?
          (to_disconnect ||= []) << allocated.delete(t)
        end
      end
      n = nil
    end

    if (n || _size) < max
      do_make_new = allocated[thread] = true
    end
  end

  if to_disconnect
    to_disconnect.each{|dconn| disconnect_connection(dconn)}
  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
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 223
def checkin_connection(conn)
  @available_connections << conn
  conn
end
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 231
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 242
def owned_connection(thread)
  sync{@allocated[thread]}
end
preconnect(concurrent = false) click to toggle source

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 248
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_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)

  unless @connection_handling == :disconnect
    checkin_connection(conn)
  end

  @waiter.signal
  nil
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 282
def sync
  @mutex.synchronize{yield}
end