Garbage collector in Android

Question

I have seen many Android answers that suggest calling the garbage collector in some situations   Is it a good practice to request the garbage collector in Android before doing a memory-hungry operation  If not  should I only call it if I get an OutOfMemory error   Are there other things I should use before resorting to the garbage collector

User · Answer

If you get an OutOfMemoryError then it s usually too late to call the garbage collector     Here is quote from Android Developer      Most of the time  garbage collection   occurs because of tons of small    short-lived objects and some garbage   collectors  like generational garbage   collectors  can optimize the   collection of these objects so that   the application does not get   interrupted too often  The Android   garbage collector is unfortunately not   able to perform such optimizations and   the creation of short-lived objects in   performance critical code paths is   thus very costly for your application    So to my understanding  there is no urgent need to call the gc  It s better to spend more effort in avoiding the unnecessary creation of objects  like creation of objects inside loops

User · Answer

Quick note for Xamarin developers   If you would like to call System gc   in Xamarin Android apps you should call Java Lang JavaSystem Gc

User · Answer

Generally speaking  in the presence of a garbage collector  it is never good practice to manually call the GC  A GC is organized around heuristic algorithms which work best when left to their own devices  Calling the GC manually often decreases performance   Occasionally  in some relatively rare situations  one may find that a particular GC gets it wrong  and a manual call to the GC may then improves things  performance-wise  This is because it is not really possible to implement a  perfect  GC which will manage memory optimally in all cases  Such situations are hard to predict and depend on many subtle implementation details  The  good practice  is to let the GC run by itself  a manual call to the GC is the exception  which should be envisioned only after an actual performance issue has been duly witnessed

User · Answer

I would say no  because the Developer docs on RAM usage state            GC EXPLICIT         An explicit GC  such as when you call gc    which you should avoid calling and instead trust the GC to run when needed                 I ve highlighted the relevant part in bold   Have a look at the YouTube series  Android Performance Patterns - it will show you tips on managing your app s memory usage  such as using Android s ArrayMaps and SparseArrays instead of HashMaps

User · Answer

Generally speaking you should not call GC explicitly with System gc    There is even the IO lecture  http   www youtube com watch v  CruQY55HOk  where they explain what the GC pauses log mean and in which they also state to never call System gc   because Dalvik knows better than you when to do so    On the other hand as mentioned in above answers already GC process in Android  like everything else  is sometimes buggy  This means Dalvik GC algorithms are not on par with Hotspot or JRockit JVMs and might get things wrong on some occasions  One of those occasions is when allocating bitmap objects  This is a tricky one because it uses Heap and Non Heap memory and because one loose instance of bitmap object on memory constrained device is enough to give you an OutOfMemory exception  So calling it after you don t need this bitmap any-more is generally suggested by many developers and is even considered good practice by some people    Better practice is using  recycle   on a bitmap as it is what this method is made for  as it marks native memory of the bitmap as safe to delete   Keep in mind that this is very version dependent  meaning it will generally be required on older Android versions  Pre 3 0 I think  but will not be required on later ones  Also it won t hurt much using it on newer versions ether  just don t do this in a loop or something like that   New ART runtime changed a lot here because they introduced special Heap  partition  for big objects but I think it will not hurt much to do this with ART ether   Also one very important note about System gc    This method is not a command that Dalvik  or JVMs  are obligated to respond to  Consider it more like saying to Virtual machine  Could you please do garbage collection if it s not a hassle

User · Answer

Out of memory in android application is very common if we not handle the bitmap properly  The solution for the problem would be   if imageBitmap    null        imageBitmap recycle        imageBitmap   null    System gc    BitmapFactory Options options   new BitmapFactory Options    options inSampleSize   3  imageBitmap   BitmapFactory decodeFile URI  options   Bitmap  scaledBitmap   Bitmap createScaledBitmap imageBitmap  200  200  true   imageView setImageBitmap scaledBitmap     In the above code Have just tried to recycle the bitmap which will allow you to free up the used memory space  so out of memory may not happen I have tried it worked for me   If still facing the problem you can also add these line as well  BitmapFactory Options options   new BitmapFactory Options    options inTempStorage   new byte 16 1024   options inPurgeable   true    for more information take a look at this link  https   web archive org web 20140514092802 http   voices yahoo com android-virtual-machine-vm-out-memory-error-7342266 html cat 59    NOTE  Due to the momentary  pause  caused by performing gc  it is not recommended to do this before each bitmap allocation   Optimum design is    Free all bitmaps that are no longer needed  by the if   recycle   nullcode shown   Make a method to help with that   System gc    Allocate the new bitmaps

User · Answer

For versions prior to 3 0 honeycomb  Yes  do call System gc     I tried to create Bitmaps  but was always getting  VM out of memory error   But  when I called System gc   first  it was OK   When creating bitmaps  Android often fails with out of memory errors  and does not try to garbage collect first  Hence  call System gc    and you have enough memory to create Bitmaps    If creating Objects  I think System gc will be called automatically if needed  but not for creating bitmaps  It just fails   So I recommend manually calling System gc   before creating bitmaps

User · Answer

My app manage a lot of images and it died with a OutOfMemoryError  This helped me  In the Manifest xml Add    lt application         android largeHeap  true  gt

User · Answer

Best way to avoid OOM during Bitmap creation   http   developer android com training displaying-bitmaps index html

User · Answer

It seems System gc   do not work on Art Android 6 0 1 Nexus 5x  So I use Runtime getRuntime   gc    instead

User · Answer

There is no need to call the garbage collector after an OutOfMemoryError   It s Javadoc clearly states      Thrown when the Java Virtual Machine cannot allocate an object because it is out of memory  and no more memory could be made available by the garbage collector    So  the garbage collector already tried to free up memory before generating the error but was unsuccessful

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