class Concurrent::Throttle

A tool managing concurrency level of tasks. The maximum capacity is set in constructor. Each acquire will lower the available capacity and release will increase it. When there is no available capacity the current thread may either be blocked or an event is returned which will be resolved when capacity becomes available.

The more common usage of the Throttle is with a proxy executor `a_throttle.on(Concurrent.global_io_executor)`. Anything executed on the proxy executor will be throttled and execute on the given executor. There can be more than one proxy executors. All abstractions which execute tasks have option to specify executor, therefore the proxy executor can be injected to any abstraction throttling its concurrency level.

{include:file:docs-source/throttle.out.md}

@!macro warn.edge

Public Class Methods

new(capacity) click to toggle source

Create throttle. @param [Integer] capacity How many tasks using this throttle can run at the same time.

Calls superclass method
# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 33
def initialize(capacity)
  super()
  @MaxCapacity            = capacity
  @Queue                  = LockFreeQueue.new
  @executor_cache         = [nil, nil]
  self.capacity = capacity
end

Public Instance Methods

acquire(timeout = nil, &block) click to toggle source

Blocks current thread until there is capacity available in the throttle. The acquired capacity has to be returned to the throttle by calling {#release}. If block is passed then the block is called after the capacity is acquired and it is automatically released after the block is executed.

@param [Numeric] timeout the maximum time in second to wait. @yield [] block to execute after the capacity is acquired @return [Object, self, true, false]

* When no timeout and no block it returns self
* When no timeout and with block it returns the result of the block
* When with timeout and no block it returns true when acquired and false when timed out
* When with timeout and with block it returns the result of the block of nil on timing out

@see release

# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 59
def acquire(timeout = nil, &block)
  event = acquire_or_event
  if event
    within_timeout = event.wait(timeout)
    # release immediately when acquired later after the timeout since it is unused
    event.on_resolution!(self, &:release) unless within_timeout
  else
    within_timeout = true
  end

  called = false
  if timeout
    if block
      if within_timeout
        called = true
        block.call
      else
        nil
      end
    else
      within_timeout
    end
  else
    if block
      called = true
      block.call
    else
      self
    end
  end
ensure
  release if called
end
acquire_or_event() click to toggle source

@!visibility private

# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 136
def acquire_or_event
  while true
    current_capacity = capacity
    if compare_and_set_capacity current_capacity, current_capacity - 1
      if current_capacity > 0
        return nil
      else
        event = Promises.resolvable_event
        @Queue.push event
        return event
      end
    end
  end
end
available_capacity() click to toggle source

@return [Integer] The available capacity.

# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 26
def available_capacity
  current_capacity = capacity
  current_capacity >= 0 ? current_capacity : 0
end
default_executor() click to toggle source

Uses executor provided by {#on} therefore all events and futures created using factory methods on this object will be throttled. Overrides {Promises::FactoryMethods#default_executor}.

@return [ExecutorService] @see Promises::FactoryMethods#default_executor

Calls superclass method
# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 179
def default_executor
  on(super)
end
inspect()
Alias for: to_s
max_capacity() click to toggle source

@return [Integer] The maximum capacity.

# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 42
def max_capacity
  @MaxCapacity
end
on(executor = Promises::FactoryMethods.default_executor) click to toggle source

@param [ExecutorService] executor @return [ExecutorService] An executor which wraps given executor and allows to post tasks only

as available capacity in the throttle allows.

@example throttling future

a_future.then_on(a_throttle.on(:io)) { a_throttled_task }
# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 158
def on(executor = Promises::FactoryMethods.default_executor)
  current_executor, current_cache = @executor_cache
  return current_cache if current_executor == executor && current_cache

  if current_executor.nil?
    # cache first proxy
    proxy_executor  = ProxyExecutor.new(self, Concurrent.executor(executor))
    @executor_cache = [executor, proxy_executor]
    return proxy_executor
  else
    # do not cache more than 1 executor
    ProxyExecutor.new(self, Concurrent.executor(executor))
  end
end
release() click to toggle source

Releases previously acquired capacity back to Throttle. Has to be called exactly once for each acquired capacity. @return [self] @see acquire_operation, acquire, try_acquire

# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 114
def release
  while true
    current_capacity = capacity
    if compare_and_set_capacity current_capacity, current_capacity + 1
      if current_capacity < 0
        # release called after trigger which pushed a trigger, busy wait is ok
        Thread.pass until (trigger = @Queue.pop)
        trigger.resolve
      end
      return self
    end
  end
end
to_s() click to toggle source

@return [String] Short string representation.

Calls superclass method
# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 129
def to_s
  format '%s capacity available %d of %d>', super[0..-2], capacity, @MaxCapacity
end
Also aliased as: inspect
try_acquire() click to toggle source

Tries to acquire capacity from the throttle. Returns true when there is capacity available. The acquired capacity has to be returned to the throttle by calling {#release}. @return [true, false] @see release

# File lib/concurrent-ruby-edge/concurrent/edge/throttle.rb, line 98
def try_acquire
  while true
    current_capacity = capacity
    if current_capacity > 0
      return true if compare_and_set_capacity(
          current_capacity, current_capacity - 1)
    else
      return false
    end
  end
end