com.trivago.triava.time

Class EstimatorTimeSource

java.lang.Object

java.lang.Thread

com.trivago.triava.time.EstimatorTimeSource

All Implemented Interfaces:

TimeSource, Runnable

public class EstimatorTimeSource
extends Thread
implements TimeSource

A TimeSource that provides the value of System.currentTimeMillis() in the given millisecond precision. Target use case for this class is to reduce the overhead of System.currentTimeMillis() or System.nanoTime(), when being called very frequently (thousands or million times per second). An own TimeSource can be given, that can replace System.currentTimeMillis().

This implementation uses a background thread to regularly fetch the current time from System.currentTimeMillis(). The value is cached and returned in all methods returning a time. Caching is helpful, as fetching the time includes a potentially expensive crossing of the operating system boundary (calling native, levering privilege, register swapping, ...). If you call it thousands or millions of times per second, this has a very noticeable effect. For these cases the throughput can be massively increased (100% or even 1000%).

Users of this class must be aware that all calls within the update interval will return exactly the same time. For example a Cache implementation that uses this class will have more entries with the identical incoming timestamp. This can have an effect on expiration or time-based eviction strategies like LRU.

Author:

cesken

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

Constructor Summary

Constructors

Constructor and Description
EstimatorTimeSource(int updateIntervalMillis) Creates a TimeSource with the given update interval, that uses the system time as TimeSource.
EstimatorTimeSource(TimeSource parentTimeSource, int updateIntervalMillis, TriavaLogger logger) Creates a TimeSource with the given update interval.

Method Summary

Modifier and Type	Method and Description
long	millis() Returns the time in milliseconds.
void	run()
long	seconds() Returns the time in seconds.
void	shutdown() Shutdown the time source.
long	time(TimeUnit tu) Returns the time in the given time unit.

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

Constructor Detail

EstimatorTimeSource

public EstimatorTimeSource(int updateIntervalMillis)

Creates a TimeSource with the given update interval, that uses the system time as TimeSource.

Parameters:

updateIntervalMillis - Update interval, which defines the approximate precision

EstimatorTimeSource

public EstimatorTimeSource(TimeSource parentTimeSource,
                           int updateIntervalMillis,
                           TriavaLogger logger)

Creates a TimeSource with the given update interval. The time is estimated on base of the given parentTimeSource, so the precision is not better than this and the parentTimeSource.

Parameters:

parentTimeSource - The TimeSource to estimate

updateIntervalMillis - Update interval, which defines the approximate precision

logger - A non-null triava logger

Method Detail

run

public void run()

Specified by:

run in interface Runnable

Overrides:

run in class Thread

shutdown

public void shutdown()

Description copied from interface: TimeSource

Shutdown the time source. Implementations should release all resources they use, like background threads, memory and connections to hardware clocks.

Specified by:

shutdown in interface TimeSource

time

public long time(TimeUnit tu)

Description copied from interface: TimeSource

Returns the time in the given time unit. It is recommended for unsupported TimeUnit values to throw an UnsupportedOperation exception.

Specified by:

time in interface TimeSource

Parameters:

tu - The time unit for the return value

Returns:

time in milliseconds since epoch

seconds

public long seconds()

Description copied from interface: TimeSource

Returns the time in seconds. Convenience method, with the same effect as passing TimeUnit.SECONDS to TimeSource.time(TimeUnit)

Specified by:

seconds in interface TimeSource

Returns:

time in seconds since epoch

millis

public long millis()

Description copied from interface: TimeSource

Returns the time in milliseconds. Convenience method, with the same effect as passing TimeUnit.MILLISECONDS TimeSource.time(TimeUnit)

Specified by:

millis in interface TimeSource

Returns:

time in milliseconds since epoch