V - The computed value of the ScheduledServicepublic abstract class ScheduledService<V> extends Service<V>
The ScheduledService is a Service which will automatically restart
itself after a successful execution, and under some conditions will
restart even in case of failure. A new ScheduledService begins in
the READY state, just as a normal Service. After calling
start or restart, the ScheduledService will
enter the SCHEDULED state for the duration specified by delay.
Once RUNNING, the ScheduledService will execute its Task. On successful
completion, the ScheduledService will transition to the SUCCEEDED state,
and then to the READY state and back to the SCHEDULED state. The amount
of time the ScheduledService will remain in this state depends on the
amount of time between the last state transition to RUNNING, and the
current time, and the period. In short, the period
defines the minimum amount of time from the start of one run and the start of
the next. If the previous execution completed before period expires,
then the ScheduledService will remain in the SCHEDULED state until the period
expires. If on the other hand the execution took longer than the
specified period, then the ScheduledService will immediately transition
back to RUNNING.
If, while RUNNING, the ScheduledService's Task throws an error or in
some other way ends up transitioning to FAILED, then the ScheduledService
will either restart or quit, depending on the values for
backoffStrategy, restartOnFailure, and
maximumFailureCount.
If a failure occurs and restartOnFailure is false, then
the ScheduledService will transition to FAILED and will stop. To restart
a failed ScheduledService, you must call restart manually.
If a failure occurs and restartOnFailure is true, then
the the ScheduledService may restart automatically. First,
the result of calling backoffStrategy will become the
new cumulativePeriod. In this way, after each failure, you can cause
the service to wait a longer and longer period of time before restarting.
Once the task completes successfully, the cumulativePeriod is reset to
the value of period.
ScheduledService defines static EXPONENTIAL_BACKOFF_STRATEGY and LOGARITHMIC_BACKOFF_STRATEGY
implementations, of which LOGARITHMIC_BACKOFF_STRATEGY is the default value for
backoffStrategy. After maximumFailureCount is reached, the
ScheduledService will transition to FAILED in exactly the same way as if
restartOnFailure were false.
If the period or delay is changed while the
ScheduledService is running, the new values will be taken into account on the
next iteration. For example, if the period is increased, then the next time the
ScheduledService enters the SCHEDULED state, the new period will be used.
Likewise, if the delay is changed, the new value will be honored on
the next restart or reset/start.
ScheduledService<Document> svc = new ScheduledService<Document>() {
protected Task<Document> createTask() {
return new Task<Document>() {
protected Document call() {
// Connect to a Server
// Get the XML document
// Parse it into a document
return document;
}
};
}
};
svc.setPeriod(Duration.seconds(1));
Timing for this class is not absolutely reliable. A very busy event thread might introduce some timing lag into the beginning of the execution of the background Task, so very small values for the period or delay are likely to be inaccurate. A delay or period in the hundreds of milliseconds or larger should be fairly reliable.
The ScheduledService in its default configuration has a default period of 0 and a
default delay of 0. This will cause the ScheduledService to execute the task immediately
upon Service.start(), and re-executing immediately upon successful completion.
For this purposes of this class, any Duration that answers true to Duration.isUnknown()
will treat that duration as if it were Duration.ZERO. Likewise, any Duration which answers true
to Duration.isIndefinite() will be treated as if it were a duration of Double.MAX_VALUE
milliseconds. Any null Duration is treated as Duration.ZERO. Any custom implementation of an backoff strategy
callback must be prepared to handle these different potential values.
The ScheduledService introduces a new property called lastValue. The lastValue is the value that
was last successfully computed. Because a Service clears its value property on each run, and
because the ScheduledService will reschedule a run immediately after completion (unless it enters the
cancelled or failed states), the value property is not overly useful on a ScheduledService. In most cases
you will want to instead use the value returned by lastValue.
Service.ready(), Service.scheduled(), Service.running(), succeeded(),
Service.cancelled(), and failed() methods are implemented in this class. Subclasses which also
override these methods must take care to invoke the super implementation.Worker.State| Modifier and Type | Field and Description |
|---|---|
static Callback<ScheduledService<?>,Duration> |
EXPONENTIAL_BACKOFF_STRATEGY
A Callback implementation for the
backoffStrategy property which
will exponentially backoff the period between re-executions in the case of
a failure. |
static Callback<ScheduledService<?>,Duration> |
LINEAR_BACKOFF_STRATEGY
A Callback implementation for the
backoffStrategy property which
will linearly backoff the period between re-executions in the case of
a failure. |
static Callback<ScheduledService<?>,Duration> |
LOGARITHMIC_BACKOFF_STRATEGY
A Callback implementation for the
backoffStrategy property which
will logarithmically backoff the period between re-executions in the case of
a failure. |
| Constructor and Description |
|---|
ScheduledService() |
addEventFilter, addEventHandler, buildEventDispatchChain, cancelled, createTask, exceptionProperty, executorProperty, fireEvent, getException, getExecutor, getMessage, getOnCancelled, getOnFailed, getOnReady, getOnRunning, getOnScheduled, getOnSucceeded, getProgress, getState, getTitle, getTotalWork, getValue, getWorkDone, isRunning, messageProperty, onCancelledProperty, onFailedProperty, onReadyProperty, onRunningProperty, onScheduledProperty, onSucceededProperty, progressProperty, ready, removeEventFilter, removeEventHandler, restart, running, runningProperty, scheduled, setEventHandler, setExecutor, setOnCancelled, setOnFailed, setOnReady, setOnRunning, setOnScheduled, setOnSucceeded, start, stateProperty, titleProperty, totalWorkProperty, valueProperty, workDonePropertypublic static final Callback<ScheduledService<?>,Duration> EXPONENTIAL_BACKOFF_STRATEGY
backoffStrategy property which
will exponentially backoff the period between re-executions in the case of
a failure. This computation takes the original period and the number of
consecutive failures and computes the backoff amount from that information.
If the service is null, then Duration.ZERO is returned. If the period is 0 then
the result of this method will simply be Math.exp(currentFailureCount). In all other cases,
the returned value is the same as {@code period + (period * Math.exp(currentFailureCount))).
public static final Callback<ScheduledService<?>,Duration> LOGARITHMIC_BACKOFF_STRATEGY
backoffStrategy property which
will logarithmically backoff the period between re-executions in the case of
a failure. This computation takes the original period and the number of
consecutive failures and computes the backoff amount from that information.
If the service is null, then Duration.ZERO is returned. If the period is 0 then
the result of this method will simply be Math.log1p(currentFailureCount). In all other cases,
the returned value is the same as {@code period + (period * Math.log1p(currentFailureCount))).
public static final Callback<ScheduledService<?>,Duration> LINEAR_BACKOFF_STRATEGY
backoffStrategy property which
will linearly backoff the period between re-executions in the case of
a failure. This computation takes the original period and the number of
consecutive failures and computes the backoff amount from that information.
If the service is null, then Duration.ZERO is returned. If the period is 0 then
the result of this method will simply be currentFailureCount. In all other cases,
the returned value is the same as {@code period + (period * currentFailureCount).
public final Duration getDelay()
public final void setDelay(Duration value)
public final ObjectProperty<Duration> delayProperty()
public final Duration getPeriod()
public final void setPeriod(Duration value)
public final ObjectProperty<Duration> periodProperty()
public final Callback<ScheduledService<?>,Duration> getBackoffStrategy()
public final void setBackoffStrategy(Callback<ScheduledService<?>,Duration> value)
public final ObjectProperty<Callback<ScheduledService<?>,Duration>> backoffStrategyProperty()
public final boolean getRestartOnFailure()
public final void setRestartOnFailure(boolean value)
public final BooleanProperty restartOnFailureProperty()
public final int getMaximumFailureCount()
public final void setMaximumFailureCount(int value)
public final IntegerProperty maximumFailureCountProperty()
public final int getCurrentFailureCount()
public final ReadOnlyIntegerProperty currentFailureCountProperty()
public final Duration getCumulativePeriod()
public final ReadOnlyObjectProperty<Duration> cumulativePeriodProperty()
public final Duration getMaximumCumulativePeriod()
public final void setMaximumCumulativePeriod(Duration value)
public final ObjectProperty<Duration> maximumCumulativePeriodProperty()
public final V getLastValue()
public final ReadOnlyObjectProperty<V> lastValueProperty()
protected void executeTask(Task<V> task)
Service
Uses the executor defined on this Service to execute the
given task. If the executor is null, then a default
executor is used which will create a new daemon thread on which to
execute this task.
This method is intended only to be called by the Service implementation.
executeTask in class Service<V>task - a non-null task to executeprotected void succeeded()
Serviceprotected void failed()
Servicepublic void reset()
Servicepublic boolean cancel()
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