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

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Subclasses:
ConnectionLeasingQueue
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 100



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 108



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


  








  

    #add_back(element)  
  



  

    

Add element to the back of the queue.  Never blocks.


  



  [ GitHub ]


  

  


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



def add_back(element)
  synchronize do
    @queue.unshift 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 59



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 52



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 91



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 120



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 86



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 113



def remove
  @queue.pop
end


  








  

    #size  
  



  

    

Number of elements in the queue.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 66



def size
  synchronize do
    @queue.size
  end
end


  








  

    #synchronize(&block)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb', line 95



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 126



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