class ActiveRecord::ConnectionAdapters::ConnectionPool::Queue

Active Record Connection Pool Queue

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

Public Class Methods

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 13
def initialize(lock = Monitor.new)
  @lock = lock
  @cond = @lock.new_cond
  @num_waiting = 0
  @queue = []
end

If timeout is not given, remove and return the head of 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:

ActiveRecord::ConnectionTimeoutError if timeout is given and no element

becomes available within timeout seconds,

size ()

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 66
def size
  synchronize do
    @queue.size
  end
end

Number of elements in the queue.

Private Instance Methods

any? ()

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 100
def any?
  !@queue.empty?
end

Test if the queue currently contains any elements.

can_remove_no_wait? ()

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 108
def can_remove_no_wait?
  @queue.size > @num_waiting
end

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.

internal_poll (timeout)

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 91
def internal_poll(timeout)
  no_wait_poll || (timeout && wait_poll(timeout))
end

no_wait_poll ()

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 120
def no_wait_poll
  remove if can_remove_no_wait?
end

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

remove ()

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 113
def remove
  @queue.pop
end

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

synchronize (&block)

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 95
def synchronize(&block)
  @lock.synchronize(&block)
end

wait_poll (timeout)

Source

# File lib/active_record/connection_adapters/abstract/connection_pool/queue.rb, line 126
def wait_poll(timeout)
  @num_waiting += 1

  t0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  elapsed = 0
  loop do
    @cond.wait(timeout - elapsed)

    return remove if any?

    elapsed = Process.clock_gettime(Process::CLOCK_MONOTONIC) - 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

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