程序包 org.apache.dubbo.common.timer

类 HashedWheelTimer

java.lang.Object

org.apache.dubbo.common.timer.HashedWheelTimer

所有已实现的接口:

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.

字段概要

字段

修饰符和类型	字段	说明
static String	NAME	may be in spi?

构造器概要

构造器

构造器	说明
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, long maxPendingTimeouts)	Creates a new timer.

方法概要

修饰符和类型	方法	说明
boolean	isStop()	the timer is stop
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.

从类继承的方法 java.lang.Object

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

字段详细资料

NAME

public static final String NAME

may be in spi?

另请参阅:

常量字段值

构造器详细资料

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.

参数:

tickDuration - the duration between tick

unit - the time unit of the tickDuration

抛出:

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()).

参数:

tickDuration - the duration between tick

unit - the time unit of the tickDuration

ticksPerWheel - the size of the wheel

抛出:

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.

参数:

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

抛出:

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.

参数:

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

抛出:

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.

参数:

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

抛出:

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,
                        long maxPendingTimeouts)

Creates a new timer.

参数:

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

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.

抛出:

NullPointerException - if either of threadFactory and unit is null

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

方法详细资料

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.

抛出:

IllegalStateException - if this timer has been stopped already

stop

public Set<Timeout> stop()

从接口复制的说明: Timer

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

指定者:

stop 在接口中 Timer

返回:

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

isStop

public boolean isStop()

从接口复制的说明: Timer

the timer is stop

指定者:

isStop 在接口中 Timer

返回:

true for stop

newTimeout

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

从接口复制的说明: Timer

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

指定者:

newTimeout 在接口中 Timer

返回:

a handle which is associated with the specified task

pendingTimeouts

public long pendingTimeouts()

Returns the number of pending timeouts of this Timer.