class Garcon::TimerTask
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 {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 `Garcon::TimeoutError` object as the third argument.
@example 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
@example 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
@example Immediate execution with ‘:run_now`
tt = Garcon::TimerTask.new(run_now: true) { puts 'GO! GO! GO!' } tt.execute # => 'GO! GO! GO!'
@example 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
@example 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...
@example 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
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 = Garcon::TimerTask.execute(execution_interval: 10) do puts 'Sappening d00d?' end task.running? # => true
# File lib/garcon/task/timer_task.rb, line 275 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
@note Calls Garcon::Dereferenceable# set_deref_options passing opts. All options supported by Garcon::Dereferenceable can be set during object initialization. @param [Hash] opts The options defining task execution. @option opts [Integer] :execution_interval The number of seconds between task executions (defaults to: EXECUTION_INTERVAL) @option opts [Integer] :timeout_interval The 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) @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. @see Garcon::Dereferenceable# 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
Public Instance Methods
Execute a previously created TimerTask
.
@example Instance and execute in separate steps
tt = Garcon::TimerTask.new(execution_interval: 10) { puts 'Sup!' } tt.running? # => false tt.execute tt.running? # => true
@example Instance and execute in one line
tt = Garcon::TimerTask.new(execution_interval: 10) { puts 'hi' }.execute tt.running? # => true
@return [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
@!attribute [rw] execution_interval
@return [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
@!attribute [rw] execution_interval
@return [Fixnum]
Number of seconds after the task completes before it is performed again.
# File lib/garcon/task/timer_task.rb, line 292 def execution_interval=(value) if (value = value.to_f) <= 0.0 raise ArgumentError.new 'must be greater than zero' else begin mutex.lock @execution_interval = value ensure mutex.unlock end end end
Is the executor running?
@return [Boolean]
True when running, false when shutting down or shutdown
# File lib/garcon/task/timer_task.rb, line 238 def running? @running.true? end
@!attribute [rw] timeout_interval
@return [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
@!attribute [rw] timeout_interval
@return [Fixnum]
Number of seconds the task can run before it is considered failed.
# File lib/garcon/task/timer_task.rb, line 318 def timeout_interval=(value) if (value = value.to_f) <= 0.0 raise ArgumentError.new('must be greater than zero') else begin mutex.lock @timeout_interval = value ensure mutex.unlock end end end