class ActiveRecord::ConnectionAdapters::ConnectionPool::Queue
Threadsafe, fair, LIFO queue. Meant to be used by ConnectionPool with which it shares a Monitor.
Public Class Methods
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 106 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 129 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 114 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 144 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 137 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 122 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 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,
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 164 def poll(timeout = nil) synchronize { internal_poll(timeout) } end
Private Instance Methods
Test if the queue currently contains any elements.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 178 def any? !@queue.empty? end
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.
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 186 def can_remove_no_wait? @queue.size > @num_waiting end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 169 def internal_poll(timeout) no_wait_poll || (timeout && wait_poll(timeout)) 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 198 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 191 def remove @queue.pop end
# File lib/active_record/connection_adapters/abstract/connection_pool.rb, line 173 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 204 def wait_poll(timeout) @num_waiting += 1 t0 = Concurrent.monotonic_time elapsed = 0 loop do ActiveSupport::Dependencies.interlock.permit_concurrent_loads do @cond.wait(timeout - elapsed) end return remove if any? elapsed = Concurrent.monotonic_time - 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