org.HdrHistogram
Class SingleWriterRecorder

java.lang.Object
  org.HdrHistogram.SingleWriterRecorder

public class SingleWriterRecorder
extends Object

Records integer values, and provides stable interval Histogram samples from live recorded data without interrupting or stalling active recording of values. Each interval histogram provided contains all value counts accumulated since the previous interval histogram was taken.

This pattern is commonly used in logging interval histogram information while recoding is ongoing.

SingleWriterRecorder expects only a single thread (the "single writer") to call recordValue(long) or recordValueWithExpectedInterval(long, long) at any point in time. It DOES NOT safely support concurrent recording calls.

Constructor Summary

SingleWriterRecorder(int numberOfSignificantValueDigits)
Construct an auto-resizing SingleWriterRecorder with a lowest discernible value of 1 and an auto-adjusting highestTrackableValue.

SingleWriterRecorder(long highestTrackableValue, int numberOfSignificantValueDigits)
Construct a SingleWriterRecorder given the highest value to be tracked and a number of significant decimal digits.

SingleWriterRecorder(long lowestDiscernibleValue, long highestTrackableValue, int numberOfSignificantValueDigits)
Construct a SingleWriterRecorder given the Lowest and highest values to be tracked and a number of significant decimal digits.

Method Summary

Histogram	getIntervalHistogram() Get a new instance of an interval histogram, which will include a stable, consistent view of all value counts accumulated since the last interval histogram was taken.
Histogram	getIntervalHistogram(Histogram histogramToRecycle) Get an interval histogram, which will include a stable, consistent view of all value counts accumulated since the last interval histogram was taken.
void	getIntervalHistogramInto(Histogram targetHistogram) Place a copy of the value counts accumulated since accumulated (since the last interval histogram was taken) into targetHistogram.
void	recordValue(long value) Record a value
void	recordValueWithExpectedInterval(long value, long expectedIntervalBetweenValueSamples) Record a value
void	reset() Reset any value counts accumulated thus far.

Methods inherited from class java.lang.Object

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

Constructor Detail

SingleWriterRecorder

public SingleWriterRecorder(int numberOfSignificantValueDigits)

Construct an auto-resizing SingleWriterRecorder with a lowest discernible value of 1 and an auto-adjusting highestTrackableValue. Can auto-reize up to track values up to (Long.MAX_VALUE / 2).

Parameters:

numberOfSignificantValueDigits - Specifies the precision to use. This is the number of significant decimal digits to which the histogram will maintain value resolution and separation. Must be a non-negative integer between 0 and 5.

SingleWriterRecorder

public SingleWriterRecorder(long highestTrackableValue,
                            int numberOfSignificantValueDigits)

Construct a SingleWriterRecorder given the highest value to be tracked and a number of significant decimal digits. The histogram will be constructed to implicitly track (distinguish from 0) values as low as 1.

Parameters:

highestTrackableValue - The highest value to be tracked by the histogram. Must be a positive integer that is >= 2.

numberOfSignificantValueDigits - Specifies the precision to use. This is the number of significant decimal digits to which the histogram will maintain value resolution and separation. Must be a non-negative integer between 0 and 5.

SingleWriterRecorder

public SingleWriterRecorder(long lowestDiscernibleValue,
                            long highestTrackableValue,
                            int numberOfSignificantValueDigits)

Construct a SingleWriterRecorder given the Lowest and highest values to be tracked and a number of significant decimal digits. Providing a lowestDiscernibleValue is useful is situations where the units used for the histogram's values are much smaller that the minimal accuracy required. E.g. when tracking time values stated in nanosecond units, where the minimal accuracy required is a microsecond, the proper value for lowestDiscernibleValue would be 1000.

Parameters:

lowestDiscernibleValue - The lowest value that can be tracked (distinguished from 0) by the histogram. Must be a positive integer that is >= 1. May be internally rounded down to nearest power of 2.

highestTrackableValue - The highest value to be tracked by the histogram. Must be a positive integer that is >= (2 * lowestDiscernibleValue).

numberOfSignificantValueDigits - Specifies the precision to use. This is the number of significant decimal digits to which the histogram will maintain value resolution and separation. Must be a non-negative integer between 0 and 5.

Method Detail

recordValue

public void recordValue(long value)

Record a value

Parameters:

value - the value to record

Throws:

ArrayIndexOutOfBoundsException - (may throw) if value is exceeds highestTrackableValue

recordValueWithExpectedInterval

public void recordValueWithExpectedInterval(long value,
                                            long expectedIntervalBetweenValueSamples)
                                     throws ArrayIndexOutOfBoundsException

Record a value

To compensate for the loss of sampled values when a recorded value is larger than the expected interval between value samples, Histogram will auto-generate an additional series of decreasingly-smaller (down to the expectedIntervalBetweenValueSamples) value records.

See related notes AbstractHistogram.recordValueWithExpectedInterval(long, long) for more explanations about coordinated opmissionand expetced interval correction. *

Parameters:

value - The value to record

expectedIntervalBetweenValueSamples - If expectedIntervalBetweenValueSamples is larger than 0, add auto-generated value records as appropriate if value is larger than expectedIntervalBetweenValueSamples

Throws:

ArrayIndexOutOfBoundsException - (may throw) if value is exceeds highestTrackableValue

getIntervalHistogram

public Histogram getIntervalHistogram()

Get a new instance of an interval histogram, which will include a stable, consistent view of all value counts accumulated since the last interval histogram was taken.

Calling getIntervalHistogram() will reset the value counts, and start accumulating value counts for the next interval.

Returns:

a histogram containing the value counts accumulated since the last interval histogram was taken.

getIntervalHistogram

public Histogram getIntervalHistogram(Histogram histogramToRecycle)

Get an interval histogram, which will include a stable, consistent view of all value counts accumulated since the last interval histogram was taken.

getIntervalHistogram(histogramToRecycle) accepts a previously returned interval histogram that can be recycled internally to avoid allocation and content copying operations, and is therefore siginificantly more efficient for repeated use than getIntervalHistogram() and getIntervalHistogramInto(). The provided histogramToRecycle must be either be null or an interval histogram returned by a previous call to getIntervalHistogram(histogramToRecycle) or getIntervalHistogram().

NOTE: The caller is responsible for not recycling the same returned interval histogram more than once. If the same interval histogram instance is recycled more than once, behavior is undefined.

Calling getIntervalHistogram(histogramToRecycle) will reset the value counts, and start accumulating value counts for the next interval

Parameters:

histogramToRecycle - a previously returned interval histogram that may be recycled to avoid allocation and copy operations.

Returns:

a histogram containing the value counts accumulated since the last interval histogram was taken.

getIntervalHistogramInto

public void getIntervalHistogramInto(Histogram targetHistogram)

Place a copy of the value counts accumulated since accumulated (since the last interval histogram was taken) into targetHistogram. Calling getIntervalHistogramInto() will reset the value counts, and start accumulating value counts for the next interval.

Parameters:

targetHistogram - the histogram into which the interval histogram's data should be copied

reset

public void reset()

Reset any value counts accumulated thus far.