class ActiveRecord::ConnectionAdapters::ConnectionPool::Queue

Threadsafe, fair, FIFO queue. Meant to be used by ConnectionPool with which it shares a Monitor. But could be a generic Queue.

The Queue in stdlib's 'thread' could replace this class except stdlib's doesn't support waiting with a timeout.

Public Class Methods

new(lock = Monitor.new) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 74
def initialize(lock = Monitor.new)
  @lock = lock
  @cond = @lock.new_cond
  @num_waiting = 0
  @queue = []
end

Public Instance Methods

add(element) click to toggle source

Add element to the queue. Never blocks.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 97
def add(element)
  synchronize do
    @queue.push element
    @cond.signal
  end
end
any_waiting?() click to toggle source

Test if any threads are currently waiting on the queue.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 82
def any_waiting?
  synchronize do
    @num_waiting > 0
  end
end
clear() click to toggle source

Remove all elements from the queue.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 112
def clear
  synchronize do
    @queue.clear
  end
end
delete(element) click to toggle source

If element is in the queue, remove and return it, or nil.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 105
def delete(element)
  synchronize do
    @queue.delete(element)
  end
end
num_waiting() click to toggle source

Returns the number of threads currently waiting on this queue.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 90
def num_waiting
  synchronize do
    @num_waiting
  end
end
poll(timeout = nil) click to toggle source

Remove the head of the queue.

If timeout is not given, remove and return the head the queue if the number of available elements is strictly greater than the number of threads currently waiting (that is, don't jump ahead in line). Otherwise, return nil.

If timeout is given, block if it there is no element available, waiting up to timeout seconds for an element to become available.

Raises:

becomes available after timeout seconds,

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 132
def poll(timeout = nil)
  synchronize do
    if timeout
      no_wait_poll || wait_poll(timeout)
    else
      no_wait_poll
    end
  end
end

Private Instance Methods

any?() click to toggle source

Test if the queue currently contains any elements.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 149
def any?
  !@queue.empty?
end
can_remove_no_wait?() click to toggle source

A thread can remove an element from the queue without waiting if an only if the number of currently available connections is strictly greater than the number of waiting threads.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 157
def can_remove_no_wait?
  @queue.size > @num_waiting
end
no_wait_poll() click to toggle source

Remove and return the head the queue if the number of available elements is strictly greater than the number of threads currently waiting. Otherwise, return nil.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 169
def no_wait_poll
  remove if can_remove_no_wait?
end
remove() click to toggle source

Removes and returns the head of the queue if possible, or nil.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 162
def remove
  @queue.shift
end
synchronize(&block) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 144
def synchronize(&block)
  @lock.synchronize(&block)
end
wait_poll(timeout) click to toggle source

Waits on the queue up to timeout seconds, then removes and returns the head of the queue.

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 175
def wait_poll(timeout)
  @num_waiting += 1

  t0 = Time.now
  elapsed = 0
  loop do
    @cond.wait(timeout - elapsed)

    return remove if any?

    elapsed = Time.now - t0
    if elapsed >= timeout
      msg = 'could not obtain a database connection within %0.3f seconds (waited %0.3f seconds)' %
        [timeout, elapsed]
      raise ConnectionTimeoutError, msg
    end
  end
ensure
  @num_waiting -= 1
end