org.threadly.concurrent.future.watchdog

Class PollingWatchdog

java.lang.Object

org.threadly.concurrent.future.watchdog.PollingWatchdog

public class PollingWatchdog
extends java.lang.Object

This class is designed to help ensure a future completes with an arbitrary condition to determine when a future should be canceled. If the condition is time based then see ConstantTimeWatchdog and MixedTimeWatchdog as possibly more efficient options. This class however can allow the condition to be independent from the submission to be watched. For example if you want to time something out after a lack of progress, but don't care about the absolute time it has been running you can track that progress and provide a Supplier to watch(Supplier, ListenableFuture) which will return true only once there has been no progress in X milliseconds. The supplier will be invoked regularly to check the state associated to the matching future.

Since:

5.40

Constructor Summary

Constructors

Constructor and Description
PollingWatchdog(long pollFrequencyMillis, boolean sendInterruptOnFutureCancel) Constructs a new PollingWatchdog.
PollingWatchdog(SubmitterScheduler scheduler, long pollFrequencyMillis, boolean sendInterruptOnFutureCancel) Constructs a new PollingWatchdog with a scheduler of your choosing.

Method Summary

Modifier and Type	Method and Description
int	getWatchingCount() Check how many futures are currently being monitored for completion.
boolean	isActive() Checks to see if this watchdog is currently active.
void	watch(java.util.function.Supplier<java.lang.Boolean> cancelTest, ListenableFuture<?> future) Watch a given ListenableFuture to ensure that it completes within the constructed time limit.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PollingWatchdog

public PollingWatchdog(long pollFrequencyMillis,
                       boolean sendInterruptOnFutureCancel)

Constructs a new PollingWatchdog. This constructor will use a default static scheduler (which is lazily constructed). This should be fine in most cases, but you can provide your own scheduler if you have specific needs where the CentralThreadlyPool default is not a good option.

Parameters:

pollFrequencyMillis - Time in milliseconds that futures will be checked if they should be timed out

sendInterruptOnFutureCancel - If true, and a thread is provided with the future, an interrupt will be sent on timeout

PollingWatchdog

public PollingWatchdog(SubmitterScheduler scheduler,
                       long pollFrequencyMillis,
                       boolean sendInterruptOnFutureCancel)

Constructs a new PollingWatchdog with a scheduler of your choosing. It is critical that this scheduler has a free thread available to inspect futures which may not have completed in the given timeout. You may want to use a org.threadly.concurrent.limiter to ensure that there are threads available.

Parameters:

scheduler - Scheduler to schedule task to look for expired futures

pollFrequencyMillis - Time in milliseconds that futures will be checked if they should be timed out

sendInterruptOnFutureCancel - If true, and a thread is provided with the future, an interrupt will be sent on timeout

Method Detail

watch

public void watch(java.util.function.Supplier<java.lang.Boolean> cancelTest,
                  ListenableFuture<?> future)

Watch a given ListenableFuture to ensure that it completes within the constructed time limit. If the future is not marked as done by the time limit then it will be completed by invoking Future.cancel(boolean). Weather a true or false will be provided to interrupt the running thread is dependent on how this PollingWatchdog was constructed.

The provided Supplier will be invoked regularly as the state is polled. Once it returns true it will never be invoked again, and instead Future.cancel(boolean) will be invoked on the provided future.

Parameters:

cancelTest - Supplier to return true when the future should be canceled

future - Future to inspect to ensure completion

isActive

public boolean isActive()

Checks to see if this watchdog is currently active. Meaning there are futures on it which either have not been completed yet, or have not been inspected for completion. If this returns false, it means that there are no futures waiting to complete, and no scheduled tasks currently scheduled to inspect them.

Returns:

true if this watchdog is currently in use

getWatchingCount

public int getWatchingCount()

Check how many futures are currently being monitored for completion.

Returns:

The number of futures being monitored