class Concurrent::TimerTask
A very common concurrency pattern is to run a thread that performs a task at regular intervals. The thread that performs the task sleeps for the given interval then wakes up and performs the task. Lather, rinse, repeat… This pattern causes two problems. First, it is difficult to test the business logic of the task because the task itself is tightly coupled with the concurrency logic. Second, an exception raised while performing the task can cause the entire thread to abend. In a long-running application where the task thread is intended to run for days/weeks/years a crashed task thread can pose a significant problem. `TimerTask` alleviates both problems.
When a `TimerTask` is launched it starts a thread for monitoring the execution interval. The `TimerTask` thread does not perform the task, however. Instead, the TimerTask launches the task on a separate thread. Should the task experience an unrecoverable crash only the task thread will crash. This makes the `TimerTask` very fault tolerant. Additionally, the `TimerTask` thread can respond to the success or failure of the task, performing logging or ancillary operations. `TimerTask` can also be configured with a timeout value allowing it to kill a task that runs too long.
One other advantage of `TimerTask` is that it forces the business logic to be completely decoupled from the concurrency logic. The business logic can be tested separately then passed to the `TimerTask` for scheduling and running.
In some cases it may be necessary for a `TimerTask` to affect its own execution cycle. To facilitate this, a reference to the TimerTask instance is passed as an argument to the provided block every time the task is executed.
The `TimerTask` class includes the `Dereferenceable` mixin module so the result of the last execution is always available via the `#value` method. Dereferencing options can be passed to the `TimerTask` during construction or at any later time using the `#set_deref_options` method.
`TimerTask` supports notification through the Ruby standard library {ruby-doc.org/stdlib-2.0/libdoc/observer/rdoc/Observable.html Observable} module. On execution the `TimerTask` will notify the observers with three arguments: time of execution, the result of the block (or nil on failure), and any raised exceptions (or nil on success). If the timeout interval is exceeded the observer will receive a `Concurrent::TimeoutError` object as the third argument.
@!macro copy_options
@example Basic usage
task = Concurrent::TimerTask.new{ puts 'Boom!' } task.execute task.execution_interval #=> 60 (default) task.timeout_interval #=> 30 (default) # wait 60 seconds... #=> 'Boom!' task.shutdown #=> true
@example Configuring `:execution_interval` and `:timeout_interval`
task = Concurrent::TimerTask.new(execution_interval: 5, timeout_interval: 5) do puts 'Boom!' end task.execution_interval #=> 5 task.timeout_interval #=> 5
@example Immediate execution with `:run_now`
task = Concurrent::TimerTask.new(run_now: true){ puts 'Boom!' } task.execute #=> 'Boom!'
@example Last `#value` and `Dereferenceable` mixin
task = Concurrent::TimerTask.new( dup_on_deref: true, execution_interval: 5 ){ Time.now } task.execute Time.now #=> 2013-11-07 18:06:50 -0500 sleep(10) task.value #=> 2013-11-07 18:06:55 -0500
@example Controlling execution from within the block
timer_task = Concurrent::TimerTask.new(execution_interval: 1) do |task| task.execution_interval.times{ print 'Boom! ' } print "\n" task.execution_interval += 1 if task.execution_interval > 5 puts 'Stopping...' task.shutdown end end timer_task.execute # blocking call - this task will stop itself #=> Boom! #=> Boom! Boom! #=> Boom! Boom! Boom! #=> Boom! Boom! Boom! Boom! #=> Boom! Boom! Boom! Boom! Boom! #=> Stopping...
@example Observation
class TaskObserver def update(time, result, ex) if result print "(#{time}) Execution successfully returned #{result}\n" elsif ex.is_a?(Concurrent::TimeoutError) print "(#{time}) Execution timed out\n" else print "(#{time}) Execution failed with error #{ex}\n" end end end task = Concurrent::TimerTask.new(execution_interval: 1, timeout_interval: 1){ 42 } task.add_observer(TaskObserver.new) task.execute #=> (2013-10-13 19:08:58 -0400) Execution successfully returned 42 #=> (2013-10-13 19:08:59 -0400) Execution successfully returned 42 #=> (2013-10-13 19:09:00 -0400) Execution successfully returned 42 task.shutdown task = Concurrent::TimerTask.new(execution_interval: 1, timeout_interval: 1){ sleep } task.add_observer(TaskObserver.new) task.execute #=> (2013-10-13 19:07:25 -0400) Execution timed out #=> (2013-10-13 19:07:27 -0400) Execution timed out #=> (2013-10-13 19:07:29 -0400) Execution timed out task.shutdown task = Concurrent::TimerTask.new(execution_interval: 1){ raise StandardError } task.add_observer(TaskObserver.new) task.execute #=> (2013-10-13 19:09:37 -0400) Execution failed with error StandardError #=> (2013-10-13 19:09:38 -0400) Execution failed with error StandardError #=> (2013-10-13 19:09:39 -0400) Execution failed with error StandardError task.shutdown
@see ruby-doc.org/stdlib-2.0/libdoc/observer/rdoc/Observable.html @see docs.oracle.com/javase/7/docs/api/java/util/TimerTask.html
Constants
- EXECUTION_INTERVAL
Default `:execution_interval` in seconds.
- TIMEOUT_INTERVAL
Default `:timeout_interval` in seconds.
Public Class Methods
Create and execute a new `TimerTask`.
@!macro timer_task_initialize
@example
task = Concurrent::TimerTask.execute(execution_interval: 10){ print "Hello World\n" } task.running? #=> true
# File lib/concurrent/timer_task.rb, line 231 def self.execute(opts = {}, &task) TimerTask.new(opts, &task).execute end
Create a new TimerTask with the given task and configuration.
@!macro [attach] timer_task_initialize
@param [Hash] opts the options defining task execution. @option opts [Integer] :execution_interval number of seconds between task executions (default: EXECUTION_INTERVAL) @option opts [Integer] :timeout_interval number of seconds a task can run before it is considered to have failed (default: TIMEOUT_INTERVAL) @option opts [Boolean] :run_now Whether to run the task immediately upon instantiation or to wait until the first # execution_interval has passed (default: false) @!macro deref_options @raise ArgumentError when no block is given. @yield to the block after :execution_interval seconds have passed since the last yield @yieldparam task a reference to the `TimerTask` instance so that the block can control its own lifecycle. Necessary since `self` will refer to the execution context of the block rather than the running `TimerTask`. @return [TimerTask] the new `TimerTask`
# File lib/concurrent/timer_task.rb, line 189 def initialize(opts = {}, &task) raise ArgumentError.new('no block given') unless block_given? super end
Public Instance Methods
Execute a previously created `TimerTask`.
@return [TimerTask] a reference to `self`
@example Instance and execute in separate steps
task = Concurrent::TimerTask.new(execution_interval: 10){ print "Hello World\n" } task.running? #=> false task.execute task.running? #=> true
@example Instance and execute in one line
task = Concurrent::TimerTask.new(execution_interval: 10){ print "Hello World\n" }.execute task.running? #=> true
# File lib/concurrent/timer_task.rb, line 214 def execute synchronize do if @running.false? @running.make_true schedule_next_task(@run_now ? 0 : @execution_interval) end end self end
@!attribute [rw] #execution_interval @return [Fixnum] Number of seconds after the task completes before the
task is performed again.
# File lib/concurrent/timer_task.rb, line 238 def execution_interval synchronize { @execution_interval } end
@!attribute [rw] #execution_interval @return [Fixnum] Number of seconds after the task completes before the
task is performed again.
# File lib/concurrent/timer_task.rb, line 245 def execution_interval=(value) if (value = value.to_f) <= 0.0 raise ArgumentError.new('must be greater than zero') else synchronize { @execution_interval = value } end end
Is the executor running?
@return [Boolean] `true` when running, `false` when shutting down or shutdown
# File lib/concurrent/timer_task.rb, line 197 def running? @running.true? end
@!attribute [rw] #timeout_interval @return [Fixnum] Number of seconds the task can run before it is
considered to have failed.
# File lib/concurrent/timer_task.rb, line 256 def timeout_interval synchronize { @timeout_interval } end
@!attribute [rw] #timeout_interval @return [Fixnum] Number of seconds the task can run before it is
considered to have failed.
# File lib/concurrent/timer_task.rb, line 263 def timeout_interval=(value) if (value = value.to_f) <= 0.0 raise ArgumentError.new('must be greater than zero') else synchronize { @timeout_interval = value } end end
Private Instance Methods
@!visibility private
# File lib/concurrent/timer_task.rb, line 306 def execute_task(completion) return nil unless @running.true? ScheduledTask.execute(execution_interval, args: [completion], &method(:timeout_task)) _success, value, reason = @executor.execute(self) if completion.try? self.value = value schedule_next_task time = Time.now observers.notify_observers do [time, self.value, reason] end end nil end
# File lib/concurrent/timer_task.rb, line 275 def ns_initialize(opts, &task) set_deref_options(opts) self.execution_interval = opts[:execution] || opts[:execution_interval] || EXECUTION_INTERVAL self.timeout_interval = opts[:timeout] || opts[:timeout_interval] || TIMEOUT_INTERVAL @run_now = opts[:now] || opts[:run_now] @executor = Concurrent::SafeTaskExecutor.new(task) @running = Concurrent::AtomicBoolean.new(false) self.observers = Collection::CopyOnNotifyObserverSet.new end
@!visibility private
# File lib/concurrent/timer_task.rb, line 294 def ns_kill_execution @running.make_false super end
@!visibility private
# File lib/concurrent/timer_task.rb, line 288 def ns_shutdown_execution @running.make_false super end
@!visibility private
# File lib/concurrent/timer_task.rb, line 300 def schedule_next_task(interval = execution_interval) ScheduledTask.execute(interval, args: [Concurrent::Event.new], &method(:execute_task)) nil end
@!visibility private
# File lib/concurrent/timer_task.rb, line 322 def timeout_task(completion) return unless @running.true? if completion.try? self.value = value schedule_next_task observers.notify_observers(Time.now, nil, Concurrent::TimeoutError.new) end end