Class: Garcon::TimerTask

Inherits:

Object

• Object
• Garcon::TimerTask

Includes:

Dereferenceable, Observable, RubyExecutor

Defined in:

lib/garcon/task/timer_task.rb

Overview

A very common currency 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. Derefencing 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). If the timeout interval is exceeded the observer will receive a `Garcon::TimeoutError` object as the third argument.

Examples:

Basic usage

tt = Garcon::TimerTask.new { puts 'Run! Go! Execute! GO! GO! GO!' }
tt.execute

tt.execution_interval # => 60 (default)
tt.timeout_interval   # => 30 (default)

# wait 60 seconds...
# => 'Run! Go! Execute! GO! GO! GO!'

tt.shutdown # => true

Configuring ‘:execution_interval` and `:timeout_interval`

tt = Garcon::TimerTask.new(execution_interval: 5, timeout_interval: 5) do
  puts 'Execute! Execute! GO! GO! GO!'
end

tt.execution_interval # => 5
tt.timeout_interval   # => 5

Immediate execution with ‘:run_now`

tt = Garcon::TimerTask.new(run_now: true) { puts 'GO! GO! GO!' }
tt.execute

# => 'GO! GO! GO!'

Last ‘#value` and `Dereferenceable` mixin

tt = Garcon::TimerTask.new(dup_on_deref: true, execution_interval: 5) do
  Time.now
end

tt.execute
Time.now   # => 2015-03-21 08:56:50 -0700
sleep(10)
tt.value   # => 2015-03-21 08:56:55 -0700

Controlling execution from within the block

timer_task = Garcon::TimerTask.new(execution_interval: 1) do |task|
  task.execution_interval.times { print 'Execute! ' }
  print "\n"
  task.execution_interval += 1
  if task.execution_interval > 5
    puts 'Executed...'
    task.shutdown
  end
end

timer_task.execute # blocking call - this task will stop itself
# => Execute!
# => Execute! Execute!
# => Execute! Execute! Execute!
# => Execute! Execute! Execute! Execute!
# => Execute! Execute! Execute! Execute! Execute!
# => Executed...

Observation

class TaskObserver
  def update(time, result, ex)
    if result
      print "(#{time}) Execution successfully returned #{result}\n"
    elsif ex.is_a?(Garcon::TimeoutError)
      print "(#{time}) Execution timed out\n"
    else
      print "(#{time}) Execution failed with error #{ex}\n"
    end
  end
end

tt = Garcon::TimerTask.new(execution_interval: 1, timeout_interval: 1) {
  42
}
tt.add_observer(TaskObserver.new)
tt.execute

# => (2015-03-21 09:06:07 -0700) Execution successfully returned 42
# => (2015-03-21 09:06:08 -0700) Execution successfully returned 42
# => (2015-03-21 09:06:09 -0700) Execution successfully returned 42
tt.shutdown

tt = Garcon::TimerTask.new(execution_interval: 1, timeout_interval: 1) {
  sleep
}
tt.add_observer(TaskObserver.new)
tt.execute

# => (2015-03-21 09:07:10 -0700) Execution timed out
# => (2015-03-21 09:07:12 -0700) Execution timed out
# => (2015-03-21 09:07:14 -0700) Execution timed out
tt.shutdown

tt = Garcon::TimerTask.new(execution_interval: 1) { raise StandardError }
tt.add_observer(TaskObserver.new)
tt.execute

# => (2015-03-21 09:12:11 -0700) Execution failed with error StandardError
# => (2015-03-21 09:12:12 -0700) Execution failed with error StandardError
# => (2015-03-21 09:12:13 -0700) Execution failed with error StandardError
tt.shutdown

Constant Summary

EXECUTION_INTERVAL =

Default :execution_interval in seconds.

60

TIMEOUT_INTERVAL =

Default :timeout_interval in seconds.

30

Constants included from RubyExecutor

RubyExecutor::FALLBACK_POLICY

Instance Attribute Summary

• #execution_interval ⇒ Fixnum

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

• #timeout_interval ⇒ Fixnum

  Number of seconds the task can run before it is considered failed.

Attributes included from Executor

#fallback_policy

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?.

Methods included from Observable

#add_observer, #count_observers, #delete_observer, #delete_observers, #with_observer

Methods included from RubyExecutor

#<<, #kill, #post, #shutdown, #shutdown?, #shuttingdown?, #wait_for_termination

Methods included from Executor

#auto_terminate?, #can_overflow?, #serialized?

Methods included from Dereferenceable

#value

Constructor Details

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

Note:

Calls Garcon::Dereferenceable# set_deref_options passing opts. All options supported by Garcon::Dereferenceable can be set during object initialization.

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) —

  The number of seconds between task executions (defaults to: EXECUTION_INTERVAL)

• :timeout_interval (Integer) —

  The number of seconds a task can run before it is considered to have failed (default: TIMEOUT_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.

See Also:

• set_deref_options

# File 'lib/garcon/task/timer_task.rb', line 215

def initialize(opts = {}, &task)
  raise ArgumentError.new('no block given') unless block_given?

  init_executor
  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 = Garcon::SafeTaskExecutor.new(task)
  @running  = Garcon::AtomicBoolean.new(false)

  self.observers = CopyOnNotifyObserverSet.new
end

Instance Attribute Details

#execution_interval ⇒ Fixnum

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

Returns:

• (Fixnum) —

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

# File 'lib/garcon/task/timer_task.rb', line 282

def execution_interval
  mutex.lock
  @execution_interval
ensure
  mutex.unlock
end

#timeout_interval ⇒ Fixnum

Returns Number of seconds the task can run before it is considered failed.

Returns:

• (Fixnum) —

  Number of seconds the task can run before it is considered failed.

# File 'lib/garcon/task/timer_task.rb', line 308

def timeout_interval
  mutex.lock
  @timeout_interval
ensure
  mutex.unlock
end

Class Method Details

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

Note:

Calls Garcon::Dereferenceable# set_deref_options passing opts. All options supported by Garcon::Dereferenceable can be set during object initialization.

Create and execute a new TimerTask.

Examples:

task = Garcon::TimerTask.execute(execution_interval: 10) do
  puts 'Sappening d00d?'
end
task.running? # => true

Parameters:

• opts (Hash) (defaults to: {}) —

  The options defining task execution.

Options Hash (opts):

• :execution_interval (Integer) —

  The number of seconds between task executions (defaults to: EXECUTION_INTERVAL)

• :timeout_interval (Integer) —

  The number of seconds a task can run before it is considered to have failed (default: TIMEOUT_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.

See Also:

• set_deref_options

# File 'lib/garcon/task/timer_task.rb', line 275

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

tt = Garcon::TimerTask.new(execution_interval: 10) { puts 'Sup!' }
tt.running? # => false
tt.execute
tt.running? # => true

Instance and execute in one line

tt = Garcon::TimerTask.new(execution_interval: 10) { puts 'hi' }.execute
tt.running? # => true

Returns:

• (TimerTask) —

  A reference to self.

# File 'lib/garcon/task/timer_task.rb', line 256

def execute
  mutex.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/garcon/task/timer_task.rb', line 238

def running?
  @running.true?
end