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

Inherits:
Object
  • Object
show all
Defined in:
activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

Overview

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.

Direct Known Subclasses

ConnectionLeasingQueue

Instance Method Summary collapse

Constructor Details

#initialize(lock = Monitor.new) ⇒ Queue

Returns a new instance of Queue.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 89

def initialize(lock = Monitor.new)
  @lock = lock
  @cond = @lock.new_cond
  @num_waiting = 0
  @queue = []
end

Instance Method Details

#add(element) ⇒ Object

Add element to the queue. Never blocks.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 112

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

#any_waiting?Boolean

Test if any threads are currently waiting on the queue.

Returns:

  • (Boolean)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 97

def any_waiting?
  synchronize do
    @num_waiting > 0
  end
end

#clearObject

Remove all elements from the queue.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 127

def clear
  synchronize do
    @queue.clear
  end
end

#delete(element) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 120

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

#num_waitingObject

Returns the number of threads currently waiting on this queue.


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

def num_waiting
  synchronize do
    @num_waiting
  end
end

#poll(timeout = nil) ⇒ Object

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:

  • ActiveRecord::ConnectionTimeoutError if timeout is given and no element

becomes available within timeout seconds,


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 147

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