MethodListener (Jikes RVM API)

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org.jikesrvm.adaptive.measurements.listeners
Class MethodListener

java.lang.Object
  org.jikesrvm.adaptive.measurements.listeners.Listener
      org.jikesrvm.adaptive.measurements.listeners.MethodListener

public final class MethodListener
extends Listener
extends Listener

A MethodListener defines a listener to collect method invocation samples. Samples are collected in a buffer. When sampleSize samples have been collected the listener's organizer is activated to process them. Defines update's interface to be a compiled method identifier, CMID.

Field Summary
`(package private) int`	`numSamples` Number of samples taken so far
`(package private) int[]`	`samples` The sample buffer Key Invariant: samples.length >= sampleSize
`(package private) int`	`sampleSize` Number of samples to be gathered before they are processed

Constructor Summary
`MethodListener(int sampleSize)`

Method Summary
`int`	`getNumSamples()`
`int[]`	`getSamples()`
`private void`	`recordSample(int CMID)` This method records a sample containing the CMID (compiled method ID) passed.
`void`	`report()` Entry point to dump what has been collected.
`void`	`reset()` Reset the buffer to prepare to take more samples.
`void`	`update(int cmid, int callerCmid, int whereFrom)` This method is called when a sample is taken.

Methods inherited from class org.jikesrvm.adaptive.measurements.listeners.Listener
`activate, activateOrganizer, isActive, passivate, setOrganizer`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

sampleSize

int sampleSize

Number of samples to be gathered before they are processed

numSamples

int numSamples

Number of samples taken so far

samples

int[] samples

The sample buffer Key Invariant: samples.length >= sampleSize

Constructor Detail

MethodListener

public MethodListener(int sampleSize)

Parameters:: sampleSize - the initial sampleSize for the listener

Method Detail

update

public void update(int cmid,
                   int callerCmid,
                   int whereFrom)

This method is called when a sample is taken. It parameter "cmid" represents the compiled method ID of the method which was executing at the time of the sample. This method bumps the counter and checks whether a threshold is reached.

NOTE: There can be multiple threads executing this method at the same time. We attempt to ensure that the resulting race conditions are safely handled, but make no guarentee that every sample is actually recorded.

Parameters:: cmid - the compiled method ID to update; callerCmid - a compiled method id for the caller, -1 if none; whereFrom - Was this a yieldpoint in a PROLOGUE, BACKEDGE, or EPILOGUE?

recordSample

private void recordSample(int CMID)

This method records a sample containing the CMID (compiled method ID) passed. Since multiple threads may be taking samples concurrently, we use fetchAndAdd to distribute indices into the buffer AND to record when a sample is taken. (Thread 1 may get an earlier index, but complete the insertion after Thread 2.)

Parameters:: CMID - compiled method ID to record

report

public void report()

Description copied from class: Listener

Entry point to dump what has been collected.

Specified by:: report in class Listener

reset

public void reset()

Reset the buffer to prepare to take more samples.

Specified by:: reset in class Listener

getSamples

public int[] getSamples()

Returns:: the buffer of samples

getNumSamples

public int getNumSamples()

Returns:: how many samples in the array returned by getSamples are valid