Eclipse Memory Analyzer Tool

Lakshman Kakkiralalittle eye labs

Agenda

● Memory Analysis● Some Definitions● An example leak code● Demo of MAT and some basic functionality

Prereqs

● Android app development● Basic Heap and Garbage Collection

Disqualification● Advanced knowledge of MAT :-)

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Why Memory Analysis?

● Identify Leaks● Reduce memory footprint

Typical problems

● Holding Context object (an Activity, a View or a Drawable)which actually happens to be an Activity

● Non-static inner classes● Caches● Aggressive Caching

Some definitions

● Shallow Size● Retained Size● Dominator● Dominator Tree ● GCRoots

Example - Object Graph

D 100 100

B100300

C 100 200

A 100 600

E 100 100

F 100 100

Example (contd) - Dominator Tree

D

B

C

A

E

F

Example - Memory Leakpublic class MainActivity extends Activity { private static LeakClass leak;

// *NOT A STATIC* class LeakClass { }

@Override public void onCreate(Bundle savedInstanceState) { ....

if (leak == null) { leak = new LeakClass(); } ... }}

Investigation Tools - LogCat

● D/dalvikvm( 9050 ): GC_CONCURRENT freed 2049K, 65% free 3571K/9991K, external 4703K/5261K, paused 2ms+2ms

Heapdump

● What - Snapshot of all the objects in the process○ Fields, References, Primitive Values○ Classes, Class Loaders

● How to generate○ DDMS view - "Dump HPROF file" icon ○ android.os.Debug.dumpHprofData(<filename>)○ signal 10

● Convert to standard HPROF format○ hprof-convert (only required if using standalone)

MAT aka Eclipse Memory Analyzer Tool

● Standalone - Download http://www.eclipse.org/mat

● Pros○ Visible Primitive Data ○ Powerful selection model○ No setup

● Cons○ Large dump files○ Cannot answer code/temporal questions

■ Who/Where/When - an object is created■ When - an object is garbage collected

Demo

Covering● View Dominator Tree● Inspector

○ look at the field values○ browse through entries in a Collection

● Class Histograms● Group by Value

Demo (contd...)

● Immediate Dominators● Path from GC roots● Retained Set● Object Query Language

References

● Google IO 2011 - "Memory Management for Android apps" http://www.google.com/events/io/2011/sessions/memory-management-for-android-apps.html

● Java Memory Analysishttp://vimeo.com/21356498

● Markus Kohler's Java Performance Bloghttp://kohlerm.blogspot.com

● Memory Analyzer Bloghttp://memoryanalyzer.blogspot.in/

Backup Slides

Application Attributes:<application android:largeHeap="true">

Garbage Collection

Pre Gingerbread:GC: stop the world gc, >100ms

Gingerbread and beyond:concurrent gc,two pauses - at the beginning and at the end < 5mspartial collections

Bitmap

pre-honeycomb:● pixel data was stored in native mem● recycle() or finalize()● invisible to MAT

honeycomb and after:● pixel data inside dalvik heap● visible to MAT● works with partial and concurrent GC

Typical Garbage Collections

GC_CONCURRENTGC_FOR_MALLOCGC_EXTERNAL_ALLOC (pre-honeycomb)GC_HPROF_DUMP_HEAP GC_EXPLICIT - app calling System.gc()