class ConnectionPool

Generic connection pool class for sharing a limited number of objects or network connections among many threads. Note: pool elements are lazily created.

Example usage with block (faster):

@pool = ConnectionPool.new { Redis.new }
@pool.with do |redis|
  redis.lpop('my-list') if redis.llen('my-list') > 0
end

Using optional timeout override (for that single invocation)

@pool.with(timeout: 2.0) do |redis|
  redis.lpop('my-list') if redis.llen('my-list') > 0
end

Example usage replacing an existing connection (slower):

$redis = ConnectionPool.wrap { Redis.new }

def do_work
  $redis.lpop('my-list') if $redis.llen('my-list') > 0
end

Accepts the following options:

:size - number of connections to pool, defaults to 5
:timeout - amount of time to wait for a connection if none currently available, defaults to 5 seconds
:auto_reload_after_fork - automatically drop all connections after fork, defaults to true

Constants

DEFAULTS
INSTANCES
VERSION

Attributes

auto_reload_after_fork[R]

Automatically drop all connections after fork

size[R]

Size of this connection pool

Public Class Methods

after_fork() click to toggle source

# File lib/connection_pool.rb, line 52
def self.after_fork
  INSTANCES.values.each do |pool|
    next unless pool.auto_reload_after_fork

    # We're on after fork, so we know all other threads are dead.
    # All we need to do is to ensure the main thread doesn't have a
    # checked out connection
    pool.checkin(force: true)
    pool.reload do |connection|
      # Unfortunately we don't know what method to call to close the connection,
      # so we try the most common one.
      connection.close if connection.respond_to?(:close)
    end
  end
  nil
end

new(options = {}, &block) click to toggle source

# File lib/connection_pool.rb, line 90
def initialize(options = {}, &block)
  raise ArgumentError, "Connection pool requires a block" unless block

  options = DEFAULTS.merge(options)

  @size = Integer(options.fetch(:size))
  @timeout = options.fetch(:timeout)
  @auto_reload_after_fork = options.fetch(:auto_reload_after_fork)

  @available = TimedStack.new(@size, &block)
  @key = :"pool-#{@available.object_id}"
  @key_count = :"pool-#{@available.object_id}-count"
  INSTANCES[self] = self if INSTANCES
end

wrap(options, &block) click to toggle source

# File lib/connection_pool.rb, line 44
def self.wrap(options, &block)
  Wrapper.new(options, &block)
end

Public Instance Methods

available() click to toggle source

Number of pool entries available for checkout at this instant.

# File lib/connection_pool.rb, line 169
def available
  @available.length
end

checkin(force: false) click to toggle source

# File lib/connection_pool.rb, line 129
def checkin(force: false)
  if ::Thread.current[@key]
    if ::Thread.current[@key_count] == 1 || force
      @available.push(::Thread.current[@key])
      ::Thread.current[@key] = nil
      ::Thread.current[@key_count] = nil
    else
      ::Thread.current[@key_count] -= 1
    end
  elsif !force
    raise ConnectionPool::Error, "no connections are checked out"
  end

  nil
end

checkout(options = {}) click to toggle source

# File lib/connection_pool.rb, line 119
def checkout(options = {})
  if ::Thread.current[@key]
    ::Thread.current[@key_count] += 1
    ::Thread.current[@key]
  else
    ::Thread.current[@key_count] = 1
    ::Thread.current[@key] = @available.pop(options[:timeout] || @timeout)
  end
end

reload(&block) click to toggle source

Reloads the ConnectionPool by passing each connection to block and then removing it the pool. Subsequent checkouts will create new connections as needed.

# File lib/connection_pool.rb, line 159
def reload(&block)
  @available.shutdown(reload: true, &block)
end

shutdown(&block) click to toggle source

Shuts down the ConnectionPool by passing each connection to block and then removing it from the pool. Attempting to checkout a connection after shutdown will raise ConnectionPool::PoolShuttingDownError.

# File lib/connection_pool.rb, line 150
def shutdown(&block)
  @available.shutdown(&block)
end

then(options = {})

Alias for: with

with(options = {}) { |conn| ... } click to toggle source

# File lib/connection_pool.rb, line 105
def with(options = {})
  Thread.handle_interrupt(Exception => :never) do
    conn = checkout(options)
    begin
      Thread.handle_interrupt(Exception => :immediate) do
        yield conn
      end
    ensure
      checkin
    end
  end
end

Also aliased as: then