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 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 91 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 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 114 def add(element) synchronize do @queue.push element @cond.signal end end
Test if any threads are currently waiting on the queue.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 99 def any_waiting? synchronize do @num_waiting > 0 end end
Remove all elements from the queue.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 129 def clear synchronize do @queue.clear end end
If element
is in the queue, remove and return it, or nil
.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 122 def delete(element) synchronize do @queue.delete(element) end end
Returns the number of threads currently waiting on this queue.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 107 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
iftimeout
is given and no element
becomes available within timeout
seconds,
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 149 def poll(timeout = nil) synchronize { internal_poll(timeout) } end
Private Instance Methods
Test if the queue currently contains any elements.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 164 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 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 172 def can_remove_no_wait? @queue.size > @num_waiting end
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 155 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 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 184 def no_wait_poll remove if can_remove_no_wait? end
Removes and returns the head of the queue if possible, or nil
.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 177 def remove @queue.shift end
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 159 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 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 190 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 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