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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.

Methods
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Class Public methods
new(lock = Monitor.new)
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 74
def initialize(lock = Monitor.new)
  @lock = lock
  @cond = @lock.new_cond
  @num_waiting = 0
  @queue = []
end
Instance Public methods
add(element)

Add element to the queue. Never blocks.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 97
def add(element)
  synchronize do
    @queue.push element
    @cond.signal
  end
end
any_waiting?()

Test if any threads are currently waiting on the queue.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 82
def any_waiting?
  synchronize do
    @num_waiting > 0
  end
end
clear()

Remove all elements from the queue.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 112
def clear
  synchronize do
    @queue.clear
  end
end
delete(element)

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

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 105
def delete(element)
  synchronize do
    @queue.delete(element)
  end
end
num_waiting()

Returns the number of threads currently waiting on this queue.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 90
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 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 it there is no element available, waiting up to timeout seconds for an element to become available.

Raises:

becomes available after timeout seconds,

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 132
def poll(timeout = nil)
  synchronize do
    if timeout
      no_wait_poll || wait_poll(timeout)
    else
      no_wait_poll
    end
  end
end