class ActiveRecord::ConnectionAdapters::ConnectionPool::Queue

Threadsafe, fair, LIFO queue. Meant to be used by ConnectionPool with which it shares a Monitor.

Public Class Methods

new(lock = Monitor.new) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 107
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 130
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 115
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 145
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 138
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 123
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 there is no element available, waiting up to timeout seconds for an element to become available.

Raises:

becomes available within timeout seconds,

# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 165
def poll(timeout = nil)
  synchronize { internal_poll(timeout) }
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 179
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 and 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 187
def can_remove_no_wait?
  @queue.size > @num_waiting
end
internal_poll(timeout) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 170
def internal_poll(timeout)
  no_wait_poll || (timeout && wait_poll(timeout))
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 199
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 192
def remove
  @queue.pop
end
synchronize(&block) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 174
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 205
def wait_poll(timeout)
  @num_waiting += 1

  t0 = Concurrent.monotonic_time
  elapsed = 0
  loop do
    ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
      @cond.wait(timeout - elapsed)
    end

    return remove if any?

    elapsed = Concurrent.monotonic_time - t0
    if elapsed >= timeout
      msg = "could not obtain a connection from the pool within %0.3f seconds (waited %0.3f seconds); all pooled connections were in use" %
        [timeout, elapsed]
      raise ConnectionTimeoutError, msg
    end
  end
ensure
  @num_waiting -= 1
end