/** {@inheritDoc} */
public RecurringTaskHandle scheduleRecurringTask(
KernelRunnable task, Identity owner, long startTime, long period) {
ScheduledTaskImpl scheduledTask =
new ScheduledTaskImpl(task, owner, defaultPriority, startTime, period);
RecurringTaskHandle handle = backingQueue.createRecurringTaskHandle(scheduledTask);
scheduledTask.setRecurringTaskHandle(handle);
return handle;
}
/** Private method to schedule the next task, if any. */
void scheduleNextTask() {
synchronized (this) {
if (queue.isEmpty()) {
inScheduler = false;
} else {
dependencyCount.decrementAndGet();
// re-set the start time before scheduling, since the
// task isn't really requested to start until all
// tasks ahead of it have run
ScheduledTaskImpl schedTask = queue.poll();
schedTask.resetStartTime();
backingQueue.addTask(schedTask);
}
}
}
/** {@inheritDoc} */
public void addTask(KernelRunnable task, Identity owner) {
ScheduledTaskImpl schedTask =
new ScheduledTaskImpl(task, owner, defaultPriority, System.currentTimeMillis());
schedTask.setTaskQueue(this);
synchronized (this) {
if (inScheduler) {
dependencyCount.incrementAndGet();
queue.offer(schedTask);
} else {
inScheduler = true;
backingQueue.addTask(schedTask);
}
}
}
/**
* Private method that determines whether a given task should be re-tried based on the given
* {@code Throwable} that caused failure. If this returns {@code true} then the task should be
* re-tried. Otherwise, the task should be dropped.
*/
private boolean shouldRetry(ScheduledTaskImpl task, Throwable t) {
// NOTE: as a first-pass implementation this simply instructs the
// caller to try again if retry is requested, but other strategies
// (like the number of times re-tried) might be considered later
if ((t instanceof ExceptionRetryStatus) && (((ExceptionRetryStatus) t).shouldRetry())) {
return true;
}
// we're not re-trying the task, so log that it's being dropped
if (logger.isLoggable(Level.WARNING)) {
if (task.isRecurring()) {
logger.logThrow(
Level.WARNING,
t,
"skipping a recurrence of "
+ "a task that failed with a non-retryable "
+ "exception: {0}",
task);
} else {
logger.logThrow(
Level.WARNING,
t,
"dropping a task that " + "failed with a non-retryable exception: {0}",
task);
}
}
return false;
}
/**
* Private method that blocks until the task has completed, re-throwing any exception resulting
* from the task failing.
*/
private void waitForTask(ScheduledTaskImpl task, boolean unbounded) throws Exception {
Throwable t = null;
try {
// NOTE: calling executeTask() directly means that we're trying
// to run the transaction in the calling thread, so there are
// actually more threads running tasks simulaneously than there
// are threads in the scheduler pool. This could be changed to
// hand-off the task and wait for the result if we wanted more
// direct control over concurrent transactions
executeTask(task, unbounded, false);
// wait for the task to complete...at this point it may have
// already completed, or else it is being re-tried in a
// scheduler thread
t = task.get();
} catch (InterruptedException ie) {
// we were interrupted, so try to cancel the task, re-throwing
// the interruption if that succeeds or looking at the result
// if the task completes before it can be cancelled
if (task.cancel(false)) {
backingQueue.notifyCancelled(task);
throw ie;
}
if (task.isCancelled()) {
throw ie;
}
t = task.get();
}
// if the result of the task was a permananent failure, then
// re-throw the exception
if (t != null) {
if (t instanceof Exception) {
throw (Exception) t;
}
throw (Error) t;
}
}
/** {@inheritDoc} */
public void run() {
logger.log(Level.FINE, "Starting a consumer for transactions");
notifyThreadJoining();
try {
while (true) {
// wait for the next task, at which point we may get
// interrupted and should therefore return
ScheduledTaskImpl task = (ScheduledTaskImpl) (backingQueue.getNextTask(true));
// run the task, checking if it completed
if (executeTask(task, false, true)) {
// if it's a recurring task, schedule the next run
if (task.isRecurring()) {
long nextStart = task.getStartTime() + task.getPeriod();
task = new ScheduledTaskImpl(task, nextStart);
backingQueue.addTask(task);
}
// if it has dependent tasks, schedule the next one
TaskQueueImpl queue = (TaskQueueImpl) (task.getTaskQueue());
if (queue != null) {
queue.scheduleNextTask();
}
}
}
} catch (InterruptedException ie) {
if (logger.isLoggable(Level.FINE)) {
logger.logThrow(Level.FINE, ie, "Consumer is finishing");
}
} catch (Exception e) {
// this should never happen, since running the task should
// never throw an exception that isn't handled
logger.logThrow(Level.SEVERE, e, "Fatal error for consumer");
} finally {
notifyThreadLeaving();
}
}
/**
* Private method that executes a single task, creating the transaction state and handling re-try
* as appropriate. If the thread calling this method is interrupted before the task can complete
* then this method attempts to re-schedule the task to run in another thread if {@code
* retryOnInterruption} is {@code true} and always re-throws the associated {@code
* InterruptedException}. Providing {@code true} for the {@code unbounded} parameter results in a
* transaction with timeout value as specified by the value of the {@code
* TransactionCoordinator.TXN_UNBOUNDED_TIMEOUT_PROPERTY} property.
*
* <p>This method returns {@code true} if the task was completed or failed permanently, and {@code
* false} otherwise. If {@code false} is returned then the task is scheduled to be re-tried at
* some point in the future, possibly by another thread, by this method. The caller may query the
* status of the task and wait for the task to complete or fail permanently through the {@code
* ScheduledTaskImpl} interface.
*/
private boolean executeTask(
ScheduledTaskImpl task, boolean unbounded, boolean retryOnInterruption)
throws InterruptedException {
logger.log(Level.FINEST, "starting a new transactional task");
// store the current owner, and then push the new thread detail
Identity parent = ContextResolver.getCurrentOwner();
ContextResolver.setTaskState(kernelContext, task.getOwner());
try {
// keep trying to run the task until we succeed, tracking how
// many tries it actually took
while (true) {
if (!task.setRunning(true)) {
// this task is already finished
return true;
}
// NOTE: We could report the two queue sizes separately,
// so we should figure out how we want to represent these
int waitSize = backingQueue.getReadyCount() + dependencyCount.get();
profileCollectorHandle.startTask(
task.getTask(), task.getOwner(), task.getStartTime(), waitSize);
task.incrementTryCount();
Transaction transaction = null;
try {
// setup the transaction state
TransactionHandle handle = transactionCoordinator.createTransaction(unbounded);
transaction = handle.getTransaction();
ContextResolver.setCurrentTransaction(transaction);
try {
// notify the profiler and access coordinator
profileCollectorHandle.noteTransactional(transaction.getId());
accessCoordinator.notifyNewTransaction(
transaction, task.getStartTime(), task.getTryCount());
// run the task in the new transactional context
task.getTask().run();
} finally {
// regardless of the outcome, always clear the current
// transaction state before proceeding...
ContextResolver.clearCurrentTransaction(transaction);
}
// try to commit the transaction...note that there's the
// chance that the application code masked the orginal
// cause of a failure, so we'll check for that first,
// re-throwing the root cause in that case
if (transaction.isAborted()) {
throw transaction.getAbortCause();
}
handle.commit();
// the task completed successfully, so we're done
profileCollectorHandle.finishTask(task.getTryCount());
task.setDone(null);
return true;
} catch (InterruptedException ie) {
// make sure the transaction was aborted
if (!transaction.isAborted()) {
transaction.abort(ie);
}
profileCollectorHandle.finishTask(task.getTryCount(), ie);
// if the task didn't finish because of the interruption
// then we want to note that and possibly re-queue the
// task to run in a usable thread
if (task.setInterrupted() && retryOnInterruption) {
if (!handoffRetry(task, ie)) {
// if the task couldn't be re-queued, then there's
// nothing left to do but drop it
task.setDone(ie);
if (logger.isLoggable(Level.WARNING)) {
logger.logThrow(Level.WARNING, ie, "dropping " + "an interrupted task: {0}" + task);
}
}
}
// always re-throw the interruption
throw ie;
} catch (Throwable t) {
// make sure the transaction was aborted
if ((transaction != null) && (!transaction.isAborted())) {
transaction.abort(t);
}
profileCollectorHandle.finishTask(task.getTryCount(), t);
// some error occurred, so see if we should re-try
if (!shouldRetry(task, t)) {
// the task is not being re-tried
task.setDone(t);
return true;
} else {
// see if the re-try should be handed-off
task.setRunning(false);
if (handoffRetry(task, t)) {
return false;
}
}
}
}
} finally {
// always restore the previous owner before leaving...
ContextResolver.setTaskState(kernelContext, parent);
}
}
