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Java game Garbage Collection

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#1 rockseller   Members   


Posted 08 December 2012 - 03:26 PM

When initializing the game, I do create temporary objects for X reasons.

When the game is ready for the main update loop, there is a series of small hiccups, that doesn't last much.

What is the best approach to eliminate these hiccups?

I was thinking in a black screen that would last X seconds once the main update loop is readt, this way the GC would enter (I hope) before I let the user play.

What do you think?

#2 PsychotikRabbit   Members   


Posted 11 December 2012 - 09:11 PM

I don't think the black screen is a good idea. At the initialization of the game you should load alll necessary objects that you will need. Then, depending on the game, you could use a cache system to access to your preloaded objects which should eliminate hiccups if you do it right. If you have to load objects at runtime, you can load it into the cache and then always access it from there. Though, you need to release objects that you don't need anymore from the cache afterward.

And by "cache" I don't mean anything complicated. It can be a hashmap of objects with names as key.

Think about it, if you have hiccups it's surely because you are loading something at each loop pass.

#3 wqking   Members   


Posted 11 December 2012 - 10:01 PM

You should avoid frequently allocate/free objects, e.g, allocate a lot of objects in each frame.
Instead, allocate some objects before entering the level and reuse them until the level is finished. That's some kind of "cache" or "pool".
Also, check if you have a lot of string "add" operation. S3 = S1 + S2 will cause dynamic memory allocation, IMO.

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#4 fae   Members   


Posted 12 December 2012 - 03:57 AM

Have you already analysed that the delay is really caused by Java garbage collection? If not, I'd really recommend analysing the problem more thoroughly before committing to any changes. There are lots of other possible causes for such delays when presenting game data to the end user, e.g. preparing the graphics context, establishing and initialising buffers in an OpenGL application etc. However we can't really speculate on these as we don't know what type of an application you have and what libraries and frameworks you're using.

Depending on the environment and SDK you could already have a suitable tool for analysing this, see http://docs.oracle.com/javase/6/docs/technotes/guides/visualvm/intro.html and http://docs.oracle.com/javase/6/docs/technotes/guides/management/jconsole.html.

IF the problem really is with GC, the recommendations above are really good. Other viable solution could be explicitly calling System.gc after the init is done. This basically asks the system to perform GC (note that it doesn't force it, the JVM is free to ignore the request). Depending on the situation this could prevent the GC from happening during the actual game logic. However the other approaches highlighted above are usually more appropriate as they limit any further GCs during the game.

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