class ActiveRecord::ConnectionAdapters::ConnectionPool::Queue
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.
Public Class Methods
# File 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
Public Instance Methods
Add element
to the queue. Never blocks.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 97 def add(element) synchronize do @queue.push element @cond.signal end end
Test if any threads are currently waiting on the queue.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 82 def any_waiting? synchronize do @num_waiting > 0 end end
Remove all elements from the queue.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 112 def clear synchronize do @queue.clear end end
If element
is in the queue, remove and return it, or nil.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 105 def delete(element) synchronize do @queue.delete(element) end end
Returns the number of threads currently waiting on this queue.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 90 def num_waiting synchronize do @num_waiting end end
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:
-
ConnectionTimeoutError if
timeout
is given and no element
becomes available after timeout
seconds,
# File 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
Private Instance Methods
Test if the queue currently contains any elements.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 149 def any? !@queue.empty? end
A thread can remove an element from the queue without waiting if an only if the number of currently available connections is strictly greater than the number of waiting threads.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 157 def can_remove_no_wait? @queue.size > @num_waiting end
Remove and return the head the queue if the number of available elements is strictly greater than the number of threads currently waiting. Otherwise, return nil.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 169 def no_wait_poll remove if can_remove_no_wait? end
Removes and returns the head of the queue if possible, or nil.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 162 def remove @queue.shift end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 144 def synchronize(&block) @lock.synchronize(&block) end
Waits on the queue up to timeout
seconds, then removes and
returns the head of the queue.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 175 def wait_poll(timeout) @num_waiting += 1 t0 = Time.now elapsed = 0 loop do @cond.wait(timeout - elapsed) return remove if any? elapsed = Time.now - t0 if elapsed >= timeout msg = 'could not obtain a database connection within %0.3f seconds (waited %0.3f seconds)' % [timeout, elapsed] raise ConnectionTimeoutError, msg end end ensure @num_waiting -= 1 end