Class HashedWheelTimer

java.lang.Object

io.netty.util.HashedWheelTimer

All Implemented Interfaces:

Timer

public class HashedWheelTimer
extends Object
implements Timer

A Timer optimized for approximated I/O timeout scheduling.

Tick Duration

As described with 'approximated', this timer does not execute the scheduled TimerTask on time. HashedWheelTimer, on every tick, will check if there are any TimerTasks behind the schedule and execute them.

You can increase or decrease the accuracy of the execution timing by specifying smaller or larger tick duration in the constructor. In most network applications, I/O timeout does not need to be accurate. Therefore, the default tick duration is 100 milliseconds and you will not need to try different configurations in most cases.

Ticks per Wheel (Wheel Size)

HashedWheelTimer maintains a data structure called 'wheel'. To put simply, a wheel is a hash table of TimerTasks whose hash function is 'dead line of the task'. The default number of ticks per wheel (i.e. the size of the wheel) is 512. You could specify a larger value if you are going to schedule a lot of timeouts.

Do not create many instances.

HashedWheelTimer creates a new thread whenever it is instantiated and started. Therefore, you should make sure to create only one instance and share it across your application. One of the common mistakes, that makes your application unresponsive, is to create a new instance for every connection.

Implementation Details

HashedWheelTimer is based on George Varghese and Tony Lauck's paper, 'Hashed and Hierarchical Timing Wheels: data structures to efficiently implement a timer facility'. More comprehensive slides are located here.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	WORKER_STATE_INIT
static final int	WORKER_STATE_SHUTDOWN
static final int	WORKER_STATE_STARTED

Constructor Summary

Constructors

Constructor	Description
HashedWheelTimer()	Creates a new timer with the default thread factory (Executors.defaultThreadFactory()), default tick duration, and default number of ticks per wheel.
HashedWheelTimer(long tickDuration, TimeUnit unit)	Creates a new timer with the default thread factory (Executors.defaultThreadFactory()) and default number of ticks per wheel.
HashedWheelTimer(long tickDuration, TimeUnit unit, int ticksPerWheel)	Creates a new timer with the default thread factory (Executors.defaultThreadFactory()).
HashedWheelTimer(ThreadFactory threadFactory)	Creates a new timer with the default tick duration and default number of ticks per wheel.
HashedWheelTimer(ThreadFactory threadFactory, long tickDuration, TimeUnit unit)	Creates a new timer with the default number of ticks per wheel.
HashedWheelTimer(ThreadFactory threadFactory, long tickDuration, TimeUnit unit, int ticksPerWheel)	Creates a new timer.
HashedWheelTimer(ThreadFactory threadFactory, long tickDuration, TimeUnit unit, int ticksPerWheel, boolean leakDetection)	Creates a new timer.
HashedWheelTimer(ThreadFactory threadFactory, long tickDuration, TimeUnit unit, int ticksPerWheel, boolean leakDetection, long maxPendingTimeouts)	Creates a new timer.
HashedWheelTimer(ThreadFactory threadFactory, long tickDuration, TimeUnit unit, int ticksPerWheel, boolean leakDetection, long maxPendingTimeouts, Executor taskExecutor)	Creates a new timer.

Method Summary

Modifier and Type	Method	Description
protected void	finalize()
Timeout	newTimeout(TimerTask task, long delay, TimeUnit unit)	Schedules the specified TimerTask for one-time execution after the specified delay.
long	pendingTimeouts()	Returns the number of pending timeouts of this Timer.
void	start()	Starts the background thread explicitly.
Set<Timeout>	stop()	Releases all resources acquired by this Timer and cancels all tasks which were scheduled but not executed yet.

Methods inherited from class Object

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

Field Details

WORKER_STATE_INIT

public static final int WORKER_STATE_INIT

See Also:

• Constant Field Values

WORKER_STATE_STARTED

public static final int WORKER_STATE_STARTED

See Also:

• Constant Field Values

WORKER_STATE_SHUTDOWN

public static final int WORKER_STATE_SHUTDOWN

See Also:

• Constant Field Values

Constructor Details

HashedWheelTimer

public HashedWheelTimer()

Creates a new timer with the default thread factory (Executors.defaultThreadFactory()), default tick duration, and default number of ticks per wheel.

HashedWheelTimer

public HashedWheelTimer(long tickDuration,
 TimeUnit unit)

Creates a new timer with the default thread factory (Executors.defaultThreadFactory()) and default number of ticks per wheel.

Parameters:

tickDuration - the duration between tick

unit - the time unit of the tickDuration

Throws:

NullPointerException - if unit is null

IllegalArgumentException - if tickDuration is <= 0

HashedWheelTimer

public HashedWheelTimer(long tickDuration,
 TimeUnit unit,
 int ticksPerWheel)

Creates a new timer with the default thread factory (Executors.defaultThreadFactory()).

Parameters:

tickDuration - the duration between tick

unit - the time unit of the tickDuration

ticksPerWheel - the size of the wheel

Throws:

NullPointerException - if unit is null

IllegalArgumentException - if either of tickDuration and ticksPerWheel is <= 0

HashedWheelTimer

public HashedWheelTimer(ThreadFactory threadFactory)

Creates a new timer with the default tick duration and default number of ticks per wheel.

Parameters:

threadFactory - a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.

Throws:

NullPointerException - if threadFactory is null

HashedWheelTimer

public HashedWheelTimer(ThreadFactory threadFactory,
 long tickDuration,
 TimeUnit unit)

Creates a new timer with the default number of ticks per wheel.

Parameters:

threadFactory - a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.

tickDuration - the duration between tick

unit - the time unit of the tickDuration

Throws:

NullPointerException - if either of threadFactory and unit is null

IllegalArgumentException - if tickDuration is <= 0

HashedWheelTimer

public HashedWheelTimer(ThreadFactory threadFactory,
 long tickDuration,
 TimeUnit unit,
 int ticksPerWheel)

Creates a new timer.

Parameters:

threadFactory - a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.

tickDuration - the duration between tick

unit - the time unit of the tickDuration

ticksPerWheel - the size of the wheel

Throws:

NullPointerException - if either of threadFactory and unit is null

IllegalArgumentException - if either of tickDuration and ticksPerWheel is <= 0

HashedWheelTimer

public HashedWheelTimer(ThreadFactory threadFactory,
 long tickDuration,
 TimeUnit unit,
 int ticksPerWheel,
 boolean leakDetection)

Creates a new timer.

Parameters:

threadFactory - a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.

tickDuration - the duration between tick

unit - the time unit of the tickDuration

ticksPerWheel - the size of the wheel

leakDetection - true if leak detection should be enabled always, if false it will only be enabled if the worker thread is not a daemon thread.

Throws:

NullPointerException - if either of threadFactory and unit is null

IllegalArgumentException - if either of tickDuration and ticksPerWheel is <= 0

HashedWheelTimer

public HashedWheelTimer(ThreadFactory threadFactory,
 long tickDuration,
 TimeUnit unit,
 int ticksPerWheel,
 boolean leakDetection,
 long maxPendingTimeouts)

Creates a new timer.

Parameters:

threadFactory - a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.

tickDuration - the duration between tick

unit - the time unit of the tickDuration

ticksPerWheel - the size of the wheel

leakDetection - true if leak detection should be enabled always, if false it will only be enabled if the worker thread is not a daemon thread.

maxPendingTimeouts - The maximum number of pending timeouts after which call to newTimeout will result in RejectedExecutionException being thrown. No maximum pending timeouts limit is assumed if this value is 0 or negative.

Throws:

NullPointerException - if either of threadFactory and unit is null

IllegalArgumentException - if either of tickDuration and ticksPerWheel is <= 0

HashedWheelTimer

public HashedWheelTimer(ThreadFactory threadFactory,
 long tickDuration,
 TimeUnit unit,
 int ticksPerWheel,
 boolean leakDetection,
 long maxPendingTimeouts,
 Executor taskExecutor)

Creates a new timer.

Parameters:

threadFactory - a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.

tickDuration - the duration between tick

unit - the time unit of the tickDuration

ticksPerWheel - the size of the wheel

leakDetection - true if leak detection should be enabled always, if false it will only be enabled if the worker thread is not a daemon thread.

maxPendingTimeouts - The maximum number of pending timeouts after which call to newTimeout will result in RejectedExecutionException being thrown. No maximum pending timeouts limit is assumed if this value is 0 or negative.

taskExecutor - The Executor that is used to execute the submitted TimerTasks. The caller is responsible to shutdown the Executor once it is not needed anymore.

Throws:

NullPointerException - if either of threadFactory and unit is null

IllegalArgumentException - if either of tickDuration and ticksPerWheel is <= 0

Method Details

finalize

protected void finalize()
                 throws Throwable

Overrides:

finalize in class Object

Throws:

Throwable

start

public void start()

Starts the background thread explicitly. The background thread will start automatically on demand even if you did not call this method.

Throws:

IllegalStateException - if this timer has been stopped already

stop

public Set<Timeout> stop()

Description copied from interface: Timer

Releases all resources acquired by this Timer and cancels all tasks which were scheduled but not executed yet.

Specified by:

stop in interface Timer

Returns:

the handles associated with the tasks which were canceled by this method

newTimeout

public Timeout newTimeout(TimerTask task,
 long delay,
 TimeUnit unit)

Description copied from interface: Timer

Schedules the specified TimerTask for one-time execution after the specified delay.

Specified by:

newTimeout in interface Timer

Returns:

a handle which is associated with the specified task

pendingTimeouts

public long pendingTimeouts()

Returns the number of pending timeouts of this Timer.