org.apache.jackrabbit.oak.stats

Class Clock

java.lang.Object

org.apache.jackrabbit.oak.stats.Clock

Direct Known Subclasses:

Clock.Fast, Clock.Virtual

public abstract class Clock
extends Object

Mechanism for keeping track of time at millisecond accuracy.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Clock.Fast Fast clock implementation whose Clock.Fast.getTime() method returns instantaneously thanks to a background task that takes care of the actual time-keeping work.
static class	Clock.Virtual A virtual clock that has no connection to the actual system time.

Field Summary

Fields

Modifier and Type	Field and Description
static Clock	ACCURATE Accurate clock implementation that uses interval timings from the System.nanoTime() method to calculate an as accurate as possible time based on occasional calls to System.currentTimeMillis() to prevent clock drift.
static Clock	SIMPLE Simple clock implementation based on System.currentTimeMillis(), which is known to be rather slow on some platforms.

Constructor Summary

Constructors

Constructor and Description
Clock()

Method Summary

Methods

Modifier and Type	Method and Description
Date	getDate() Convenience method that returns the getTime() value as a Date instance.
Date	getDateIncreasing() Convenience method that returns the getTimeIncreasing() value as a Date instance.
Date	getDateMonotonic() Convenience method that returns the getTimeMonotonic() value as a Date instance.
abstract long	getTime() Returns the current time in milliseconds since the epoch.
long	getTimeIncreasing() Returns a strictly increasing timestamp based on the current time.
long	getTimeMonotonic() Returns a monotonically increasing timestamp based on the current time.
void	waitUntil(long timestamp) Waits until the given point in time is reached.

Methods inherited from class java.lang.Object

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

Field Detail

SIMPLE

public static Clock SIMPLE

Simple clock implementation based on System.currentTimeMillis(), which is known to be rather slow on some platforms.

ACCURATE

public static Clock ACCURATE

Accurate clock implementation that uses interval timings from the System.nanoTime() method to calculate an as accurate as possible time based on occasional calls to System.currentTimeMillis() to prevent clock drift.

Constructor Detail

Clock

public Clock()

Method Detail

getTime

public abstract long getTime()

Returns the current time in milliseconds since the epoch.

Returns:

current time in milliseconds since the epoch

See Also:

System.currentTimeMillis()

getTimeMonotonic

public long getTimeMonotonic()

Returns a monotonically increasing timestamp based on the current time. A call to this method will always return a value that is greater than or equal to a value returned by any previous call. This contract holds even across multiple threads and in cases when the system time is adjusted backwards. In the latter case the returned value will remain constant until the previously reported timestamp is again reached.

Returns:

monotonically increasing timestamp

getTimeIncreasing

public long getTimeIncreasing()
                       throws InterruptedException

Returns a strictly increasing timestamp based on the current time. This method is like getTimeMonotonic(), with the exception that two calls of this method will never return the same timestamp. Instead this method will explicitly wait until the current time increases beyond any previously returned value. Note that the wait may last long if this method is called frequently from many concurrent thread or if the system time is adjusted backwards. The caller should be prepared to deal with an explicit interrupt in such cases.

Returns:

strictly increasing timestamp

Throws:

InterruptedException - if the wait was interrupted

getDate

public Date getDate()

Convenience method that returns the getTime() value as a Date instance.

Returns:

current time

getDateMonotonic

public Date getDateMonotonic()

Convenience method that returns the getTimeMonotonic() value as a Date instance.

Returns:

monotonically increasing time

getDateIncreasing

public Date getDateIncreasing()
                       throws InterruptedException

Convenience method that returns the getTimeIncreasing() value as a Date instance.

Returns:

strictly increasing time

Throws:

InterruptedException

waitUntil

public void waitUntil(long timestamp)
               throws InterruptedException

Waits until the given point in time is reached. The current thread is suspended until the getTimeIncreasing() method returns a time that's equal or greater than the given point in time.

Parameters:

timestamp - time in milliseconds since epoch

Throws:

InterruptedException - if the wait was interrupted