Package org.apache.jackrabbit.oak.stats

Class Clock

  • Direct Known Subclasses:
    Clock.Fast, Clock.Virtual
    public abstract class Clock
extends java.time.Clock
    Mechanism for keeping track of time at millisecond accuracy.

    As of Oak 1.20, this extends from Clock.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class 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 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 Description
      Clock()  

    • Method Summary

      All Methods Instance Methods Abstract Methods Concrete Methods 
      Modifier and Type Method Description
      java.util.Date getDate()
      Convenience method that returns the getTime() value as a Date instance.
      java.util.Date getDateIncreasing()
      Convenience method that returns the getTimeIncreasing() value as a Date instance.
      java.util.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.
      java.time.ZoneId getZone()  
      java.time.Instant instant()  
      void waitUntil​(long timestamp)
      Waits until the given point in time is reached.
      java.time.Clock withZone​(java.time.ZoneId zone)  

      • Methods inherited from class java.time.Clock

        equals, fixed, hashCode, millis, offset, system, systemDefaultZone, systemUTC, tick, tickMillis, tickMinutes, tickSeconds

      • Methods inherited from class java.lang.Object

        getClass, 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(), Clock.millis()

      • 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 java.lang.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:
        java.lang.InterruptedException - if the wait was interrupted

      • getDate

        public java.util.Date getDate()
        Convenience method that returns the getTime() value as a Date instance.
        Returns:
        current time

      • getDateMonotonic

        public java.util.Date getDateMonotonic()
        Convenience method that returns the getTimeMonotonic() value as a Date instance.
        Returns:
        monotonically increasing time

      • getDateIncreasing

        public java.util.Date getDateIncreasing()
                                 throws java.lang.InterruptedException
        Convenience method that returns the getTimeIncreasing() value as a Date instance.
        Returns:
        strictly increasing time
        Throws:
        java.lang.InterruptedException

      • waitUntil

        public void waitUntil​(long timestamp)
               throws java.lang.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:
        java.lang.InterruptedException - if the wait was interrupted

      • getZone

        public java.time.ZoneId getZone()
        Specified by:
        getZone in class java.time.Clock

      • instant

        public java.time.Instant instant()
        Specified by:
        instant in class java.time.Clock

      • withZone

        public java.time.Clock withZone​(java.time.ZoneId zone)
        Specified by:
        withZone in class java.time.Clock