Package org.apache.sis.internal.system

Class DelayedExecutor

java.lang.Object

java.lang.Thread

org.apache.sis.internal.system.DelayedExecutor

All Implemented Interfaces:

Runnable

public final class DelayedExecutor
extends Thread

A thread executing short tasks after some (potentially zero nanosecond) delay. This class should be reserved to internal SIS usage without user's code. In practice some user code may be indirectly executed through SIS tasks invoking overrideable methods. But all submitted tasks shall be very quick, since there is only one thread shared by everyone.

The methods for use in this class are:

• schedule(DelayedRunnable)

Comparison with java.util.concurrent

We tried to use ScheduledThreadPoolExecutor in a previous SIS version, but its "fixed-sized pool" design forces us to use only one thread if we do not want to waste resources (profiling shows that even a single thread has very low activity), which reduces the interest of that class. Combination of ThreadPoolExecutor super-class with DelayedQueue were not successful neither.

Given that:

• it seems difficult to configure (Scheduled)ThreadPoolExecutor in such a way that two or more threads are created only when really needed,
• using those executor services seems an overkill when the pool size is fixed to one thread,
• our profiling has show very low activity for that single thread anyway,
• we do not need cancellation and shutdown services for house keeping tasks (this is a daemon thread),

a more lightweight solution seems acceptable here. Pseudo-benchmarking using the CacheTest.stress() tests suggests that the lightweight solution is faster.

Since:

0.3

Version:

0.7

Author:

Martin Desruisseaux (Geomatys)

See Also:

• SIS-76

Nested Class Summary

Nested classes/interfaces inherited from class java.lang.Thread

Thread.State, Thread.UncaughtExceptionHandler

Field Summary

Fields inherited from class java.lang.Thread

MAX_PRIORITY, MIN_PRIORITY, NORM_PRIORITY

Method Summary

Modifier and Type	Method	Description
protected final boolean	isKillRequested()	Returns true if this daemon thread shall terminate.
protected boolean	isStalled()	Returns true if this thread seems to be stalled.
final void	run()	Loop to be run during the virtual machine lifetime.
static void	schedule(DelayedRunnable task)	Schedules the given short task for later execution in a daemon thread.

Methods inherited from class java.lang.Thread

activeCount, checkAccess, clone, countStackFrames, currentThread, destroy, dumpStack, enumerate, getAllStackTraces, getContextClassLoader, getDefaultUncaughtExceptionHandler, getId, getName, getPriority, getStackTrace, getState, getThreadGroup, getUncaughtExceptionHandler, holdsLock, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, resume, setContextClassLoader, setDaemon, setDefaultUncaughtExceptionHandler, setName, setPriority, setUncaughtExceptionHandler, sleep, sleep, start, stop, stop, suspend, toString, yield

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Details

schedule

public static void schedule(DelayedRunnable task)

Schedules the given short task for later execution in a daemon thread. The task will be executed after the delay specified by DelayedRunnable.getDelay(TimeUnit) The task must completes quickly, because we will typically use only one thread for all submitted tasks. Completion of the task shall not be of critical importance, because the JVM is allowed to shutdown before task completion.

Parameters:

task - the task to schedule for later execution.

run

public final void run()

Loop to be run during the virtual machine lifetime. Public as an implementation side-effect; do not invoke explicitly!

Specified by:

run in interface Runnable

isStalled

protected boolean isStalled()

Returns true if this thread seems to be stalled. This method checks the head of the queue. If the delay for that head has expired and the head is not removed in the next 5 seconds, then we will presume that the thread is stalled or dead.

Returns:

true if this thread seems to be stalled.

isKillRequested

protected final boolean isKillRequested()

Returns true if this daemon thread shall terminate. This happen at shutdown time.

Returns:

true if this daemon thread shall terminate.