Avoiding memory leaks in AndroidDenis ZhuchinskiProm.ua

d.zhuchinskiy@smartweb.com.uahttps://github.com/zhuchinskyi/https://ua.linkedin.com/in/denys-zhuchinskyi-96ab0673

Agenda

● Memory Management

● Garbage Collector

● Memory Leaks

● Tools

● Demo

● How to avoid OutOfMemoryError?

Memory Management

Android Memory Management

● Each app process is forked from an existing process

called Zygote

● No swap space

● Virtual Address Space (Memory management unit)

● Paging and Memory-Mapping (mmapping)

● Process space limitation

Sharing Memory

● Binder IPC Driver

● Android shares the same dynamic RAM across

processes using explicitly allocated shared memory

regions (ashmem)

● Most static data is mmapped into a process (VM code,

app resources, native code)

Application Memory Restrictions

● Isolated in process

● Hard limit heap size

● Heap size limit varies between devices

● Low-Memory Killer (Proportional Set Size)

ActivityManager.getMemoryClass()

ActivityManager.getLargeMemoryClass()

Process Priority

Activity Process

Visible Process

Service Process

Background Process

Empty Process

Critical Priority

High Priority

Low Priority

Main Process Memory Areas

● Stack (local variables, partial results, method invocation)

● Heap (all objects)

○ Java

○ Native

● java.lang.StackOverFlow

● java.lang.OutOfMemoryError

Main Process Memory Areas

● Stack (local variables, partial results, method invocation)

● Heap (all objects)

○ Java

○ Native

● java.lang.StackOverFlow

● java.lang.OutOfMemoryError

Garbage Collection

Garbage Collection

● Automatic memory management scheme

● VM performs routine garbage collection (GC)

● Uses mark-and-sweep algorithm

Dalvik and ART

ART GC Enhancement

● Enumerates all allocated objects and marks all reachable objects in

only one pause while Dalvik’s GC pauses twice

○ enumeration phase performed by application○ pre-cleaning technique

● Parallelization

● Lower total GC time (cleaning up recently-allocated)

● Compacting GC merges freed-up single blocks in one location of

memory

(Still in development by Android Open-Source Project)

ART GC Enhancement

Memory Leaks

● Memory leak: situation where some objects are not used by

application any more, but GC fails to recognize them as unused

● Memory consumption increases -> Degradation in performance

● GC does not prevent leaks!

Memory Leaks

How to detect?

● Huge memory consumption in Android Studio Memory Monitor

● Frequent GC calls in LogCat

● App crashes with an OutOfMemmoryError (OOM)

D/dalvikvm: <GC_Reason> <Amount_freed>, <Heap_stats>, <External_memory_stats>, <Pause_time>

07-02 15:56:14.275: D/dalvikvm(30615): GC_FOR_ALLOC freed 4442K, 25% free 20183K/26856K, paused 24ms, total 24ms07-02 15:56:16.785: I/dalvikvm-heap(30615): Grow heap (frag case) to 38.179MB for 8294416-byte allocation07-02 15:56:17.225: I/dalvikvm-heap(30615): Grow heap (frag case) to 48.279MB for 7361296-byte allocation07-02 15:56:17.625: I/Choreographer(30615): Skipped 35 frames! The application may be doing too much work on its main thread.07-02 15:56:19.035: D/dalvikvm(30615): GC_CONCURRENT freed 35838K, 43% free 51351K/89052K, paused 3ms+5ms, total 106ms

I/art: <GC_Reason> <GC_Name> <Objects_freed>(<Size_freed>) AllocSpace Objects, Large_objects_freed> (<Large_object_size_freed>) <Heap_stats> LOS objects, <Pause_time(s)>

07-02 16:00:44.531: I/art(198): Explicit concurrent mark sweep GC freed 700(30KB) AllocSpace objects, 0(0B) LOS objects, 792% free, 18MB/21MB, paused 186us total 12.763ms07-02 16:00:44.545: I/art(198): Explicit concurrent mark sweep GC freed 7(240B) AllocSpace objects, 0(0B) LOS objects, 792% free, 18MB/21MB, paused 198us total 9.465ms07-02 16:00:44.554: I/art(198): Explicit concurrent mark sweep GC freed 5(160B) AllocSpace objects, 0(0B) LOS objects, 792% free, 18MB/21MB, paused 224us total 9.045ms

Dalvik GC Reason

● GC_CONCURRENT

● GC_FOR_MALLOC

● GC_HPROF_DUMP_HEAP

● GC_EXPLICIT

● GC_EXTERNAL_ALLOC

D/dalvikvm: <GC_Reason> <Amount_freed>, <Heap_stats>, <External_memory_stats>, <Pause_time>

ART GC Reason

● Concurrent

● Alloc

● Explicit

● NativeAlloc

● CollectorTransition

● HomogeneousSpaceCompact

I/art: <GC_Reason> <GC_Name> <Objects_freed>(<Size_freed>) AllocSpace Objects, Large_objects_freed> (<Large_object_size_freed>) <Heap_stats> LOS objects, <Pause_time(s)>

Tools

Tools

● adb shell dumpsys meminfo <package_name | pid>

● Android Monitor

○ Heap Dump

○ Allocation Tracker

● Eclipse Memory Analyzer Tool (MAT)

● LeakCanary (Square)

Demo

https://github.com/zhuchinskyi/MemoryLeakSample.git

● Do not keep long-lived references to an Activity, Context, View, Drawable...

● Avoid non-static inner classes in an activity if you don’t control their life cycle

● Avoid mutable static fields

● Use Weak References

● Try to not have long living objects

● Use as much as possible application Context instead of Activity

● Remember to call unregisterReceiver() after calling registerReceiver()

● Implement cancellation policies for background threads

● Use LeakCanary in the QA cycle

● Keep an eye on the heap while the app is running

● Don’t assume GC will clean up all for you!

● Search for memory leaks even when things aren't failing!

How to avoid Memory Leaks?

● Use bitmaps with correct resolution

● Recycle the bitmaps more often, instead of just onDestroy()

● Send large files to server by chunks

● Avoid creating unnecessary objects

● Check the available heap of your application

● Coordinate with the system by implementing onTrimMemory() callback

● External libraries should be used carefully

● Use Proguard and zipalign

How to avoid OutofMemoryError?

References

● http://developer.android.com/intl/ru/training/articles/memory.html

● https://xakep.ru/2014/05/21/excurse-in-android-architecture/

● https://software.intel.com/en-us/android/articles/art-vs-dalvik-introducing-the-new-android-x86-runtime

● https://software.intel.com/en-us/android/articles/tips-for-optimizing-android-application-memory-usage

● https://android.googlesource.com/platform/art/+/master/runtime/gc/

● http://developer.android.com/intl/ru/tools/debugging/debugging-memory.html

● http://www.raizlabs.com/dev/2014/03/wrangling-dalvik-memory-management-in-android-part-1-of-2/

● https://acadgild.com/blog/analyze-manage-android-devices-memory-allocation-through-ddms-mat/

● http://developer.android.com/intl/ru/tools/help/am-memory.html

● http://developer.android.com/tools/debugging/debugging-memory.html

Q&A