javax.enterprise.concurrent

Interface ManagedTaskListener

public interface ManagedTaskListener

A ManagedTaskListener is used to monitor the state of a task's Future. It can be registered with a ManagedExecutorService using the submit methods and will be invoked when the state of the Future changes. Each listener method will run with unspecified context. All listeners run without an explicit transaction (they do not enlist in the application component's transaction). If a transaction is required, use a UserTransaction instance.

Each listener instance will be invoked within the same process in which the listener was registered. If a single listener is submitted to multiple ManagedExecutorService instances, the listener object may be invoked concurrently by multiple threads.

Each listener method supports a minimum quality of service of at-most-once. A listener is not guaranteed to be invoked due to a process failure or termination.

State Transition Diagram

The following state transition figure and tables describe the possible task lifecycle events that can occur when a ManagedTaskListener is associated with a task. Each method is invoked when the state of the Future moves from one state to another.

A. The task runs normally:

Sequence	State	Action	Listener	Next state
1.	None	submit()	taskSubmitted	Submitted
2.	Submitted	About to call run()	taskStarting	Started
3.	Started	Exit run()	taskDone	Done

B. The task is cancelled during taskSubmitted():

Sequence	State	Action	Listener	Next state
1.	None	submit()	taskSubmitted Future is cancelled.	Cancelling
2.	Cancelling		taskAborted	Cancelled
3.	Cancelled		taskDone	Done

C. The task is cancelled or aborted after submitted, but before started:

Sequence	State	Action	Listener	Next state
1.	None	submit()	taskSubmitted	Submitted
2.	Submitted	cancel() or abort	taskAborted	Cancelled
3.	Cancelled		taskDone	Done

D. The task is cancelled when it is starting:

Sequence	State	Action	Listener	Next state
1.	None	submit()	taskSubmitted	Submitted
2.	Submitted	About to call run()	taskStarting Future is cancelled.	Cancelling
3.	Cancelling		taskAborted	Cancelled
4.	Cancelled		taskDone	Done

Since:

1.0

Method Summary

Modifier and Type	Method and Description
void	taskAborted(Future<?> future, ManagedExecutorService executor, Object task, Throwable exception) Called when a task's Future has been cancelled anytime during the life of a task.
void	taskDone(Future<?> future, ManagedExecutorService executor, Object task, Throwable exception) Called when a submitted task has completed running, either successfully or failed due to any exception thrown from the task, task being cancelled, rejected, or aborted.
void	taskStarting(Future<?> future, ManagedExecutorService executor, Object task) This method is called before the task is about to start.
void	taskSubmitted(Future<?> future, ManagedExecutorService executor, Object task) Called after the task has been submitted to the Executor.

Method Detail

taskSubmitted

void taskSubmitted(Future<?> future,
                   ManagedExecutorService executor,
                   Object task)

Called after the task has been submitted to the Executor. The task will not enter the starting state until the taskSubmitted listener has completed. This method may be called from the same thread that the task was submitted with.

This event does not indicate that the task has been scheduled for execution.

Parameters:

future - the Future instance that was created when the task was submitted.

executor - the executor used to run the associated Future.

task - the task that was submitted.

taskAborted

void taskAborted(Future<?> future,
                 ManagedExecutorService executor,
                 Object task,
                 Throwable exception)

Called when a task's Future has been cancelled anytime during the life of a task. This method may be called after taskDone(). The Future.isCancelled() method returns false if the task was aborted through another means other than Future.cancel(boolean). The exception argument will represent the cause of the cancellation:

• CancellationException if the task was cancelled,
• SkippedException if the task was skipped or
• AbortedException if the task failed to start for another reason.

The AbortedException.getCause() method will return the exception that caused the task to fail to start.

Parameters:

future - the Future instance that was created when the task was submitted.

executor - the executor used to run the associated Future.

task - the task that was submitted.

exception - the cause of the task abort.

taskDone

void taskDone(Future<?> future,
              ManagedExecutorService executor,
              Object task,
              Throwable exception)

Called when a submitted task has completed running, either successfully or failed due to any exception thrown from the task, task being cancelled, rejected, or aborted.

Parameters:

future - the Future instance that was created when the task was submitted.

executor - the executor used to run the associated Future.

task - the task that was submitted.

exception - if not null, the exception that caused the task to fail.

taskStarting

void taskStarting(Future<?> future,
                  ManagedExecutorService executor,
                  Object task)

This method is called before the task is about to start. The task will not enter the starting state until the taskSubmitted listener has completed. This method may be called from the same thread that the task was submitted with.

Parameters:

future - the Future instance that was created when the task was submitted.

executor - the executor used to run the associated Future.

task - the task that was submitted.