Class: Mongo::Server::ConnectionPool

Inherits:
Object
  • Object
show all
Extended by:
Forwardable
Includes:
Loggable, Monitoring::Publishable
Defined in:
lib/mongo/server/connection_pool.rb

Overview

Represents a connection pool for server connections.

Since:

  • 2.0.0, largely rewritten in 2.9.0

Constant Summary collapse

DEFAULT_MAX_SIZE =

The default max size for the connection pool.

Since:

  • 2.9.0

5.freeze
DEFAULT_MIN_SIZE =

The default min size for the connection pool.

Since:

  • 2.9.0

0.freeze
DEFAULT_WAIT_TIMEOUT =

The default timeout, in seconds, to wait for a connection.

This timeout applies while in flow threads are waiting for background threads to establish connections (and hence they must connect, handshake and auth in the allotted time).

It is currently set to 10 seconds. The default connect timeout is 10 seconds by itself, but setting large timeouts can get applications in trouble if their requests get timed out by the reverse proxy, thus anything over 15 seconds is potentially dangerous.

Since:

  • 2.9.0

10.freeze

Constants included from Loggable

Loggable::PREFIX

Instance Attribute Summary collapse

Attributes included from Monitoring::Publishable

#monitoring

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Monitoring::Publishable

#publish_cmap_event, #publish_event, #publish_sdam_event

Methods included from Loggable

#log_debug, #log_error, #log_fatal, #log_info, #log_warn, #logger

Constructor Details

#initialize(server, options = {}) ⇒ ConnectionPool

Create the new connection pool.

Note: Additionally, options for connections created by this pool should

be included in the options passed here, and they will be forwarded to
any connections created by the pool.

Parameters:

  • server (Server) —

    The server which this connection pool is for.

  • options (Hash) (defaults to: {}) —

    The connection pool options.

Options Hash (options):

  • :max_size (Integer) —

    The maximum pool size.

  • :max_pool_size (Integer) —

    Deprecated. The maximum pool size. If max_size is also given, max_size and max_pool_size must be identical.

  • :min_size (Integer) —

    The minimum pool size.

  • :min_pool_size (Integer) —

    Deprecated. The minimum pool size. If min_size is also given, min_size and min_pool_size must be identical.

  • :wait_timeout (Float) —

    The time to wait, in seconds, for a free connection.

  • :wait_queue_timeout (Float) —

    Deprecated. Alias for :wait_timeout. If both wait_timeout and wait_queue_timeout are given, their values must be identical.

  • :max_idle_time (Float) —

    The time, in seconds, after which idle connections should be closed by the pool.

Since:

  • 2.0.0, API changed in 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 80

def initialize(server, options = {})
  unless server.is_a?(Server)
    raise ArgumentError, 'First argument must be a Server instance'
  end
  options = options.dup
  if options[:min_size] && options[:min_pool_size] && options[:min_size] != options[:min_pool_size]
    raise ArgumentError, "Min size #{options[:min_size]} is not identical to min pool size #{options[:min_pool_size]}"
  end
  if options[:max_size] && options[:max_pool_size] && options[:max_size] != options[:max_pool_size]
    raise ArgumentError, "Max size #{options[:max_size]} is not identical to max pool size #{options[:max_pool_size]}"
  end
  if options[:wait_timeout] && options[:wait_queue_timeout] && options[:wait_timeout] != options[:wait_queue_timeout]
    raise ArgumentError, "Wait timeout #{options[:wait_timeout]} is not identical to wait queue timeout #{options[:wait_queue_timeout]}"
  end
  options[:min_size] ||= options[:min_pool_size]
  options.delete(:min_pool_size)
  options[:max_size] ||= options[:max_pool_size]
  options.delete(:max_pool_size)
  if options[:min_size] && options[:max_size] &&
    options[:min_size] > options[:max_size]
  then
    raise ArgumentError, "Cannot have min size #{options[:min_size]} exceed max size #{options[:max_size]}"
  end
  if options[:wait_queue_timeout]
    options[:wait_timeout] ||= options[:wait_queue_timeout]
  end
  options.delete(:wait_queue_timeout)

  @server = server
  @options = options.freeze

  @generation = 1
  @closed = false

  # A connection owned by this pool should be either in the
  # available connections array (which is used as a stack)
  # or in the checked out connections set.
  @available_connections = available_connections = []
  @checked_out_connections = Set.new
  @pending_connections = Set.new

  # Mutex used for synchronizing access to @available_connections and
  # @checked_out_connections. The pool object is thread-safe, thus
  # all methods that retrieve or modify instance variables generally
  # must do so under this lock.
  @lock = Mutex.new

  # Condition variable broadcast when a connection is added to
  # @available_connections, to wake up any threads waiting for an
  # available connection when pool is at max size
  @available_semaphore = Semaphore.new

  # Background thread reponsible for maintaining the size of
  # the pool to at least min_size
  @populator = Populator.new(self, options)
  @populate_semaphore = Semaphore.new

  ObjectSpace.define_finalizer(self, self.class.finalize(@available_connections, @pending_connections, @populator))

  publish_cmap_event(
    Monitoring::Event::Cmap::PoolCreated.new(@server.address, options, self)
  )

  @populator.run! if min_size > 0
end

Instance Attribute Details

#generation ⇒ Integer (readonly)

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Returns generation Generation of connections currently being used by the queue.

Returns:

  • (Integer) —

    generation Generation of connections currently being used by the queue.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 194

def generation
  @generation
end

#options ⇒ Hash (readonly)

Returns options The pool options.

Returns:

  • (Hash) —

    options The pool options.

Since:

  • 2.0.0, largely rewritten in 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 147

def options
  @options
end

#populate_semaphore ⇒ Object (readonly)

Condition variable broadcast when the size of the pool changes to wake up the populator

Since:

  • 2.0.0, largely rewritten in 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 53

def populate_semaphore
  @populate_semaphore
end

#populator ⇒ Object (readonly)

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Since:

  • 2.0.0, largely rewritten in 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 257

def populator
  @populator
end

Class Method Details

.finalize(available_connections, pending_connections, populator) ⇒ Proc

Finalize the connection pool for garbage collection.

Parameters:

  • available_connections (List<Mongo::Connection>) —

    The available connections.

  • pending_connections (List<Mongo::Connection>) —

    The pending connections.

  • populator (Populator) —

    The populator.

Returns:

  • (Proc) —

    The Finalizer.

Since:

  • 2.0.0, largely rewritten in 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 666

def self.finalize(available_connections, pending_connections, populator)
  proc do
    populator.stop!

    available_connections.each do |connection|
      connection.disconnect!(reason: :pool_closed)
    end
    available_connections.clear

    pending_connections.each do |connection|
      connection.disconnect!(reason: :pool_closed)
    end
    pending_connections.clear

    # Finalizer does not close checked out connections.
    # Those would have to be garbage collected on their own
    # and that should close them.
  end
end

Instance Method Details

#available_count ⇒ Integer

Number of available connections in the pool.

Returns:

  • (Integer) —

    Number of available connections.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 225

def available_count
  raise_if_closed!

  @lock.synchronize do
    @available_connections.length
  end
end

#check_in(connection) ⇒ Object

Check a connection back into the pool.

The connection must have been previously created by this pool.

Parameters:

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 398

def check_in(connection)
  check_invariants

  @lock.synchronize do
    unless connection.connection_pool == self
      raise ArgumentError, "Trying to check in a connection which was not checked out by this pool: #{connection} checked out from pool #{connection.connection_pool} (for #{self})"
    end

    unless @checked_out_connections.include?(connection)
      raise ArgumentError, "Trying to check in a connection which is not currently checked out by this pool: #{connection} (for #{self})"
    end

    # Note: if an event handler raises, resource will not be signaled.
    # This means threads waiting for a connection to free up when
    # the pool is at max size may time out.
    # Threads that begin waiting after this method completes (with
    # the exception) should be fine.

    @checked_out_connections.delete(connection)
    publish_cmap_event(
      Monitoring::Event::Cmap::ConnectionCheckedIn.new(@server.address, connection.id, self)
    )

    if closed?
      connection.disconnect!(reason: :pool_closed)
      return
    end

    if connection.closed?
      # Connection was closed - for example, because it experienced
      # a network error. Nothing else needs to be done here.
      @populate_semaphore.signal
    elsif connection.generation != @generation
      connection.disconnect!(reason: :stale)
      @populate_semaphore.signal
    else
      connection.record_checkin!
      @available_connections << connection

      # Wake up only one thread waiting for an available connection,
      # since only one connection was checked in.
      @available_semaphore.signal
    end
  end
ensure
  check_invariants
end

#check_out ⇒ Mongo::Server::Connection

Checks a connection out of the pool.

If there are active connections in the pool, the most recently used connection is returned. Otherwise if the connection pool size is less than the max size, creates a new connection and returns it. Otherwise waits up to the wait timeout and raises Timeout::Error if there are still no active connections and the pool is at max size.

The returned connection counts toward the pool’s max size. When the caller is finished using the connection, the connection should be checked back in via the check_in method.

Returns:

Raises:

  • (Error::PoolClosedError) —

    If the pool has been closed.

  • (Timeout::Error) —

    If the connection pool is at maximum size and remains so for longer than the wait timeout.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 277

def check_out
  check_invariants

  publish_cmap_event(
    Monitoring::Event::Cmap::ConnectionCheckOutStarted.new(@server.address)
  )

  if closed?
    publish_cmap_event(
      Monitoring::Event::Cmap::ConnectionCheckOutFailed.new(
        @server.address,
        Monitoring::Event::Cmap::ConnectionCheckOutFailed::POOL_CLOSED
      ),
    )
    raise Error::PoolClosedError.new(@server.address, self)
  end

  deadline = Time.now + wait_timeout
  connection = nil
  # It seems that synchronize sets up its own loop, thus a simple break
  # is insufficient to break the outer loop
  catch(:done) do
    loop do
      # Lock must be taken on each iteration, rather for the method
      # overall, otherwise other threads will not be able to check in
      # a connection while this thread is waiting for one.
      @lock.synchronize do
        until @available_connections.empty?
          connection = @available_connections.pop

          if connection.generation != generation
            # Stale connections should be disconnected in the clear
            # method, but if any don't, check again here
            connection.disconnect!(reason: :stale)
            @populate_semaphore.signal
            next
          end

          if max_idle_time && connection.last_checkin &&
            Time.now - connection.last_checkin > max_idle_time
          then
            connection.disconnect!(reason: :idle)
            @populate_semaphore.signal
            next
          end

          @pending_connections << connection
          throw(:done)
        end

        # Ruby does not allow a thread to lock a mutex which it already
        # holds.
        if unsynchronized_size < max_size
          connection = create_connection
          @pending_connections << connection
          throw(:done)
        end
      end

      wait = deadline - Time.now
      if wait <= 0
        publish_cmap_event(
          Monitoring::Event::Cmap::ConnectionCheckOutFailed.new(
            @server.address,
            Monitoring::Event::Cmap::ConnectionCheckOutFailed::TIMEOUT,
          ),
        )

        msg = @lock.synchronize do
          "Timed out attempting to check out a connection " +
            "from pool for #{@server.address} after #{wait_timeout} sec. " +
            "Connections in pool: #{@available_connections.length} available, " +
            "#{@checked_out_connections.length} checked out, " +
            "#{@pending_connections.length} pending " +
            "(max size: #{max_size})"
        end
        raise Error::ConnectionCheckOutTimeout.new(msg, address: @server.address)
      end
      @available_semaphore.wait(wait)
    end
  end

  begin
    connect_connection(connection)
  rescue Exception
    # Handshake or authentication failed
    @lock.synchronize do
      @pending_connections.delete(connection)
    end
    @populate_semaphore.signal

    publish_cmap_event(
      Monitoring::Event::Cmap::ConnectionCheckOutFailed.new(
        @server.address,
        Monitoring::Event::Cmap::ConnectionCheckOutFailed::CONNECTION_ERROR
      ),
    )
    raise
  end

  @lock.synchronize do
    @checked_out_connections << connection
    @pending_connections.delete(connection)
  end

  publish_cmap_event(
    Monitoring::Event::Cmap::ConnectionCheckedOut.new(@server.address, connection.id, self),
  )

  connection
ensure
  check_invariants
end

#clear(options = nil) ⇒ true Also known as: disconnect!

Closes all idle connections in the pool and schedules currently checked out connections to be closed when they are checked back into the pool. The pool remains operational and can create new connections when requested.

Parameters:

  • options (Hash) (defaults to: nil) —

    a customizable set of options

Options Hash (options):

  • :lazy (true | false) —

    If true, do not close any of the idle connections and instead let them be closed during a subsequent check out operation.

  • :stop_populator (true | false) —

    Whether to stop the populator background thread. For internal driver use only.

Returns:

  • (true) —

    true.

Since:

  • 2.1.0



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# File 'lib/mongo/server/connection_pool.rb', line 460

def clear(options = nil)
  raise_if_closed!

  check_invariants

  if options && options[:stop_populator]
    stop_populator
  end

  @lock.synchronize do
    @generation += 1

    publish_cmap_event(
      Monitoring::Event::Cmap::PoolCleared.new(@server.address)
    )

    unless options && options[:lazy]
      until @available_connections.empty?
        connection = @available_connections.pop
        connection.disconnect!(reason: :stale)
        @populate_semaphore.signal
      end
    end
  end

  true
ensure
  check_invariants
end

#close(options = nil) ⇒ true

Marks the pool closed, closes all idle connections in the pool and schedules currently checked out connections to be closed when they are checked back into the pool. If force option is true, checked out connections are also closed. Attempts to use the pool after it is closed will raise Error::PoolClosedError.

Parameters:

  • options (Hash) (defaults to: nil) —

    a customizable set of options

Options Hash (options):

  • :force (true | false) —

    Also close all checked out connections.

Returns:

  • (true) —

    Always true.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 506

def close(options = nil)
  return if closed?

  options ||= {}

  stop_populator

  @lock.synchronize do
    until @available_connections.empty?
      connection = @available_connections.pop
      connection.disconnect!(reason: :pool_closed)
    end

    if options[:force]
      until @checked_out_connections.empty?
        connection = @checked_out_connections.take(1).first
        connection.disconnect!(reason: :pool_closed)
        @checked_out_connections.delete(connection)
      end
    end

    # mark pool as closed before releasing lock so
    # no connections can be created, checked in, or checked out
    @closed = true
  end

  publish_cmap_event(
    Monitoring::Event::Cmap::PoolClosed.new(@server.address, self)
  )

  true
end

#close_idle_sockets ⇒ Object

Close sockets that have been open for longer than the max idle time,

if the option is set.

Since:

  • 2.5.0



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# File 'lib/mongo/server/connection_pool.rb', line 582

def close_idle_sockets
  return if closed?
  return unless max_idle_time

  @lock.synchronize do
    i = 0
    while i < @available_connections.length
      connection = @available_connections[i]
      if last_checkin = connection.last_checkin
        if (Time.now - last_checkin) > max_idle_time
          connection.disconnect!(reason: :idle)
          @available_connections.delete_at(i)
          @populate_semaphore.signal
          next
        end
      end
      i += 1
    end
  end
end

#closed? ⇒ true | false

Whether the pool has been closed.

Returns:

  • (true | false) —

    Whether the pool is closed.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 238

def closed?
  !!@closed
end

#inspect ⇒ String

Get a pretty printed string inspection for the pool.

Examples:

Inspect the pool.

pool.inspect

Returns:

  • (String) —

    The pool inspection.

Since:

  • 2.0.0



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# File 'lib/mongo/server/connection_pool.rb', line 547

def inspect
  if closed?
    "#<Mongo::Server::ConnectionPool:0x#{object_id} min_size=#{min_size} max_size=#{max_size} " +
      "wait_timeout=#{wait_timeout} closed>"
  else
    "#<Mongo::Server::ConnectionPool:0x#{object_id} min_size=#{min_size} max_size=#{max_size} " +
      "wait_timeout=#{wait_timeout} current_size=#{size} available=#{available_count}>"
  end
end

#max_idle_time ⇒ Float | nil

The maximum seconds a socket can remain idle since it has been checked in to the pool, if set.

Returns:

  • (Float | nil) —

    The max socket idle time in seconds.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 185

def max_idle_time
  @max_idle_time ||= options[:max_idle_time]
end

#max_size ⇒ Integer

Get the maximum size of the connection pool.

Returns:

  • (Integer) —

    The maximum size of the connection pool.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 157

def max_size
  @max_size ||= options[:max_size] || [DEFAULT_MAX_SIZE, min_size].max
end

#min_size ⇒ Integer

Get the minimum size of the connection pool.

Returns:

  • (Integer) —

    The minimum size of the connection pool.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 166

def min_size
  @min_size ||= options[:min_size] || DEFAULT_MIN_SIZE
end

#populate ⇒ true | false

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Creates and adds a connection to the pool, if the pool’s size is below min_size. Retries once if a socket-related error is encountered during this process and raises if a second error or a non socket-related error occurs.

Used by the pool populator background thread.

occured, or the non socket-related error

Returns:

  • (true | false) —

    Whether this method should be called again to create more connections.

Raises:

Since:

  • 2.0.0, largely rewritten in 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 640

def populate
  return false if closed?

  begin
    return create_and_add_connection
  rescue Error::SocketError, Error::SocketTimeoutError => e
    # an error was encountered while connecting the connection,
    # ignore this first error and try again.
    log_warn("Populator failed to connect a connection for #{address}: #{e.class}: #{e}. It will retry.")
  end

  return create_and_add_connection
rescue Error::AuthError, Error
  # wake up one thread waiting for connections, since one could not
  # be created here, and can instead be created in flow
  @available_semaphore.signal
  raise
end

#size ⇒ Integer

Size of the connection pool.

Includes available and checked out connections.

Returns:

  • (Integer) —

    Size of the connection pool.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 203

def size
  raise_if_closed!

  @lock.synchronize do
    unsynchronized_size
  end
end

#stop_populator ⇒ Object

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Stop the background populator thread and clean up any connections created which have not been connected yet.

Used when closing the pool or when terminating the bg thread for testing purposes. In the latter case, this method must be called before the pool is used, to ensure no connections in pending_connections were created in-flow by the check_out method.

Since:

  • 2.0.0, largely rewritten in 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 612

def stop_populator
  @populator.stop!

  @lock.synchronize do
    # If stop_populator is called while populate is running, there may be
    # connections waiting to be connected, connections which have not yet
    # been moved to available_connections, or connections moved to available_connections
    # but not deleted from pending_connections. These should be cleaned up.
    until @pending_connections.empty?
      connection = @pending_connections.take(1).first
      connection.disconnect!
      @pending_connections.delete(connection)
    end
  end
end

#summary ⇒ Object

Note:

This method is experimental and subject to change.

Since:

  • 2.11.0



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# File 'lib/mongo/server/connection_pool.rb', line 246

def summary
  @lock.synchronize do
    "#<ConnectionPool size=#{unsynchronized_size} (#{min_size}-#{max_size}) " +
      "used=#{@checked_out_connections.length} avail=#{@available_connections.length} pending=#{@pending_connections.length}>"
  end
end

#wait_timeout ⇒ Float

The time to wait, in seconds, for a connection to become available.

Returns:

  • (Float) —

    The queue wait timeout.

Since:

  • 2.9.0



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# File 'lib/mongo/server/connection_pool.rb', line 175

def wait_timeout
  @wait_timeout ||= options[:wait_timeout] || DEFAULT_WAIT_TIMEOUT
end

#with_connection ⇒ Object

Yield the block to a connection, while handling check in/check out logic.

Examples:

Execute with a connection.

pool.with_connection do |connection|
  connection.read
end

Returns:

  • (Object) —

    The result of the block.

Since:

  • 2.0.0



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# File 'lib/mongo/server/connection_pool.rb', line 567

def with_connection
  raise_if_closed!

  connection = check_out
  yield(connection)
ensure
  if connection
    check_in(connection)
  end
end