org.apache.hadoop.util

Class GcTimeMonitor

java.lang.Object

java.lang.Thread

org.apache.hadoop.util.GcTimeMonitor

All Implemented Interfaces:

Runnable

public class GcTimeMonitor
extends Thread

This class monitors the percentage of time the JVM is paused in GC within the specified observation window, say 1 minute. The user can provide a hook which will be called whenever this percentage exceeds the specified threshold.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	GcTimeMonitor.GcData Encapsulates data about GC pauses measured at the specific timestamp.
static interface	GcTimeMonitor.GcTimeAlertHandler The user can provide an instance of a class implementing this interface when initializing a GcTimeMonitor to receive alerts when GC time percentage exceeds the specified threshold.

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
GcTimeMonitor(long observationWindowMs, long sleepIntervalMs, int maxGcTimePercentage, GcTimeMonitor.GcTimeAlertHandler alertHandler) Create an instance of GCTimeMonitor.

Method Summary

Methods

Modifier and Type	Method and Description
GcTimeMonitor.GcData	getLatestGcData() Returns a copy of the most recent data measured by this monitor.
void	run()
void	shutdown()

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

GcTimeMonitor

public GcTimeMonitor(long observationWindowMs,
             long sleepIntervalMs,
             int maxGcTimePercentage,
             GcTimeMonitor.GcTimeAlertHandler alertHandler)

Create an instance of GCTimeMonitor. Once it's started, it will stay alive and monitor GC time percentage until shutdown() is called. If you don't put a limit on the number of GCTimeMonitor instances that you create, and alertHandler != null, you should necessarily call shutdown() once the given instance is not needed. Otherwise, you may create a memory leak, because each running GCTimeMonitor will keep its alertHandler object in memory, which in turn may reference and keep in memory many more other objects.

Parameters:

observationWindowMs - the interval over which the percentage of GC time should be calculated. A practical value would be somewhere between 30 sec and several minutes.

sleepIntervalMs - how frequently this thread should wake up to check GC timings. This is also a frequency with which alertHandler will be invoked if GC time percentage exceeds the specified limit. A practical value would likely be 500..1000 ms.

maxGcTimePercentage - A GC time percentage limit (0..100) within observationWindowMs. Once this is exceeded, alertHandler will be invoked every sleepIntervalMs milliseconds until GC time percentage falls below this limit.

alertHandler - a single method in this interface is invoked when GC time percentage exceeds the specified limit.

Method Detail

run

public void run()

Specified by:

run in interface Runnable

Overrides:

run in class Thread

shutdown

public void shutdown()

getLatestGcData

public GcTimeMonitor.GcData getLatestGcData()

Returns a copy of the most recent data measured by this monitor.