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Class: ActiveRecord::ConnectionAdapters::ConnectionPool::Queue

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Subclasses:
Inherits: Object
Defined in: activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb

Overview

Active Record Connection Pool Queue

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

Class Method Summary

Instance Attribute Summary

  • #any_waiting? ⇒ Boolean readonly

    Test if any threads are currently waiting on the queue.

  • #any? ⇒ Boolean readonly private

    Test if the queue currently contains any elements.

  • #can_remove_no_wait? ⇒ Boolean readonly private

    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.

Instance Method Summary

Constructor Details

.new(lock = Monitor.new) ⇒ Queue

[ GitHub ]

  
# File 'activerecord/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

Instance Attribute Details

#any?Boolean (readonly, private)

Test if the queue currently contains any elements.

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 85

def any?
  !@queue.empty?
end

#any_waiting?Boolean (readonly)

Test if any threads are currently waiting on the queue.

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 21

def any_waiting?
  synchronize do
    @num_waiting > 0
  end
end

#can_remove_no_wait?Boolean (readonly, private)

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.

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 93

def can_remove_no_wait?
  @queue.size > @num_waiting
end

Instance Method Details

#add(element)

Add element to the queue. Never blocks.

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 36

def add(element)
  synchronize do
    @queue.push element
    @cond.signal
  end
end

#clear

Remove all elements from the queue.

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 51

def clear
  synchronize do
    @queue.clear
  end
end

#delete(element)

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 44

def delete(element)
  synchronize do
    @queue.delete(element)
  end
end

#internal_poll(timeout) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 76

def internal_poll(timeout)
  no_wait_poll || (timeout && wait_poll(timeout))
end

#no_wait_poll (private)

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.

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 105

def no_wait_poll
  remove if can_remove_no_wait?
end

#num_waiting

Returns the number of threads currently waiting on this queue.

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 29

def num_waiting
  synchronize do
    @num_waiting
  end
end

#poll(timeout = nil)

Remove the head of the queue.

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:

becomes available within timeout seconds,

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 71

def poll(timeout = nil)
  synchronize { internal_poll(timeout) }
end

#remove (private)

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 98

def remove
  @queue.pop
end

#synchronize(&block) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 80

def synchronize(&block)
  @lock.synchronize(&block)
end

#wait_poll(timeout) (private)

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 111

def wait_poll(timeout)
  @num_waiting += 1

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

    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