Class: SidekiqUniqueJobs::TimerTask

Inherits:

Concurrent::RubyExecutorService

• Object
• Concurrent::RubyExecutorService
• SidekiqUniqueJobs::TimerTask

Includes:

Concurrent::Concern::Dereferenceable, Concurrent::Concern::Observable

Defined in:

lib/sidekiq_unique_jobs/timer_task.rb

Overview

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.

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 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).

Examples:

Basic usage

task = Concurrent::TimerTask.new{ puts 'Boom!' }
task.execute

task.execution_interval #=> 60 (default)

# wait 60 seconds...
#=> 'Boom!'

task.shutdown #=> true

Configuring ‘:execution_interval`

task = Concurrent::TimerTask.new(execution_interval: 5) do
       puts 'Boom!'
     end

task.execution_interval #=> 5

Immediate execution with ‘:run_now`

task = Concurrent::TimerTask.new(run_now: true){ puts 'Boom!' }
task.execute

#=> 'Boom!'

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

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...

Observation

class TaskObserver
  def update(time, result, ex)
    if result
      print "(#{time}) Execution successfully returned #{result}\n"
    else
      print "(#{time}) Execution failed with error #{ex}\n"
    end
  end
end

task = Concurrent::TimerTask.new(execution_interval: 1){ 42 }
task.add_observer(TaskObserver.new)
task.execute
sleep 4

#=> (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){ 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 Also:

• http://ruby-doc.org/stdlib-2.0/libdoc/observer/rdoc/Observable.html
• http://docs.oracle.com/javase/7/docs/api/java/util/TimerTask.html

Constant Summary

EXECUTION_INTERVAL =

Default ‘:execution_interval` in seconds.

60

TIMEOUT_INTERVAL =

Default ‘:timeout_interval` in seconds.

30

Instance Attribute Summary

• #execution_interval ⇒ Fixnum

  Number of seconds after the task completes before the task is performed again.

Class Method Summary

• .execute(opts = {}) {|task| ... } ⇒ TimerTask

  Create and execute a new ‘TimerTask`.

Instance Method Summary

• #execute ⇒ TimerTask

  Execute a previously created ‘TimerTask`.

• #initialize(opts = {}) {|task| ... } ⇒ TimerTask constructor

  Create a new TimerTask with the given task and configuration.

• #running? ⇒ Boolean

  Is the executor running?.

Constructor Details

#initialize(opts = {}) {|task| ... } ⇒ TimerTask

Create a new TimerTask with the given task and configuration.

Parameters:

• opts (Hash) (defaults to: {}) —

  the options defining task execution.

Options Hash (opts):

• :execution_interval (Integer) —

  number of seconds between task executions (default: EXECUTION_INTERVAL)

• :run_now (Boolean) —

  Whether to run the task immediately upon instantiation or to wait until the first # execution_interval has passed (default: false)

Yields:

• to the block after :execution_interval seconds have passed since the last yield

Yield Parameters:

• 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`.

Raises:

• ArgumentError when no block is given.

# File 'lib/sidekiq_unique_jobs/timer_task.rb', line 181

def initialize(opts = {}, &task)
  raise ArgumentError, "no block given" unless task

  super
  set_deref_options opts
end

Instance Attribute Details

#execution_interval ⇒ Fixnum

Returns Number of seconds after the task completes before the task is performed again.

Returns:

• (Fixnum) —

  Number of seconds after the task completes before the task is performed again.

# File 'lib/sidekiq_unique_jobs/timer_task.rb', line 232

def execution_interval
  synchronize { @execution_interval }
end

Class Method Details

.execute(opts = {}) {|task| ... } ⇒ TimerTask

Create and execute a new ‘TimerTask`.

Examples:

task = Concurrent::TimerTask.execute(execution_interval: 10){ print "Hello World\n" }
task.running? #=> true

Parameters:

• opts (Hash) (defaults to: {}) —

  the options defining task execution.

Options Hash (opts):

• :execution_interval (Integer) —

  number of seconds between task executions (default: EXECUTION_INTERVAL)

• :run_now (Boolean) —

  Whether to run the task immediately upon instantiation or to wait until the first # execution_interval has passed (default: false)

Yields:

• to the block after :execution_interval seconds have passed since the last yield

Yield Parameters:

• 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`.

Returns:

• (TimerTask) —

  the new ‘TimerTask`

Raises:

• ArgumentError when no block is given.

# File 'lib/sidekiq_unique_jobs/timer_task.rb', line 225

def self.execute(opts = {}, &task)
  TimerTask.new(opts, &task).execute
end

Instance Method Details

#execute ⇒ TimerTask

Execute a previously created ‘TimerTask`.

Examples:

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

Instance and execute in one line

task = Concurrent::TimerTask.new(execution_interval: 10){ print "Hello World\n" }.execute
task.running? #=> true

Returns:

• (TimerTask) —

  a reference to ‘self`

# File 'lib/sidekiq_unique_jobs/timer_task.rb', line 208

def execute
  synchronize do
    if @running.false?
      @running.make_true
      schedule_next_task(@run_now ? 0 : @execution_interval)
    end
  end
  self
end

#running? ⇒ Boolean

Is the executor running?

Returns:

• (Boolean) —

  ‘true` when running, `false` when shutting down or shutdown

# File 'lib/sidekiq_unique_jobs/timer_task.rb', line 191

def running?
  @running.true?
end