org.apache.brooklyn.util.javalang

Class MemoryUsageTracker

java.lang.Object

org.apache.brooklyn.util.javalang.MemoryUsageTracker

public class MemoryUsageTracker
extends java.lang.Object

Tracks the amount of memory consumed by the given objects in use.

In one tracker, WeakReferences are used internally, so that shortly after a track(Object, long)ed object is GC'd, the getBytesUsed() value decrements appropriately.

In another we let clients listen for SoftReference expiration again using weak references.

Both only work with clients who opt-in with calls to these methods/instances.

This also includes a technique for clearing soft references. If you have access to a console you can force it with: org.apache.brooklyn.util.javalang.MemoryUsageTracker.forceClearSoftReferences()

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	MemoryUsageTracker.SoftUsageTracker Tracking for soft usage through SoftlyPresent instances

Field Summary

Fields

Modifier and Type	Field and Description
static MemoryUsageTracker	SOFT_REFERENCES Shared instance for use for tracking memory used by SoftReference.

Constructor Summary

Constructors

Constructor and Description
MemoryUsageTracker()

Method Summary

Modifier and Type	Method and Description
static java.lang.String	forceClearSoftReferences() forces all soft references to be cleared by trying to allocate an enormous chunk of memory, returns a description of what was done (tune with forceClearSoftReferences(long, int) for greater than 200M precision in the output message, if you really care about that)
static java.lang.String	forceClearSoftReferences(long headroom, int maxChunk) as forceClearSoftReferences() but gives control over headroom and max chunk size.
long	getBytesUsed()
void	track(java.lang.Object instance, long bytesUsedByInstance)

Methods inherited from class java.lang.Object

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

Field Detail

SOFT_REFERENCES

public static final MemoryUsageTracker SOFT_REFERENCES

Shared instance for use for tracking memory used by SoftReference.

Callers should only use this field to track(Object, long) objects which have (or will soon have) given up their strong references, so that only soft or weak references remain. Provided size estimates are accurate, getBytesUsed() will report the amount of used memory which is reclaimable by collecting soft references.

This is particularly handy for tracking SoftReferences, because otherwise you can quickly get to a state where Runtime.freeMemory() looks very low.

Also consider forceClearSoftReferences() to get useful information.

Constructor Detail

MemoryUsageTracker

public MemoryUsageTracker()

Method Detail

track

public void track(java.lang.Object instance,
                  long bytesUsedByInstance)

getBytesUsed

public long getBytesUsed()

forceClearSoftReferences

public static java.lang.String forceClearSoftReferences()

forces all soft references to be cleared by trying to allocate an enormous chunk of memory, returns a description of what was done (tune with forceClearSoftReferences(long, int) for greater than 200M precision in the output message, if you really care about that)

forceClearSoftReferences

public static java.lang.String forceClearSoftReferences(long headroom,
                                                        int maxChunk)

as forceClearSoftReferences() but gives control over headroom and max chunk size. it tries to undershoot by headroom as it approaches maximum (and then overshoot) to minimize the chance we take exactly all the memory and starve another thread; and it uses the given max chunk size in cases where the caller wants more precision (the available memory will be fragmented so the smaller the chunks the more it can fill in, but at the expense of time and actual memory provisioned)