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Garbage Collection

We've been spending an excessive amount of time tuning our ga...

Garbage Collection

We've been spending an excessive amount of time tuning our garbage collection and memory management of the new iOS VM based on profiler output. This is one of the cool features in the approach we took (translating Java to C rather than going directly to machine code), we can use Apple's nifty profiling tools to see where the CPU/GPU spend their time.

After quite a few profiling sessions it became apparent that the GC is the main reason for the performance overhead. Further digging showed that mutexes were the real issue here.
Our GC is non-blocking and concurrent which means it runs in a separate thread and never stops the world during collection. However, in order to track all the memory we use a wrapper around malloc which has to be threadsafe and stores all the objects allocated. This allows our memory sweep algorithm to remove all objects that are no longer used, the problem is that access to this global pool must be synchronized...

To solve this problem we rethought the basic concept behind this, now the pool is managed by a single thread that stores/removes elements. Every thread has a set of objects that it allocated since the last GC and every time a GC runs it copies the newly created objects to the global sweep pool and wipes the slate. This effectively removes all synchronization from the very expensive allocation process which is pretty cool.

On a separate subject our Codename One workshop for JavaZone just got accepted, that is pretty cool!
I really enjoyed JavaZone last year and felt it exceeded JavaOne in many aspects. This would actually be a workshop session where you can learn Codename One programming from me in person, it would be great seeing Codename One developers there.

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Posted by Shai Almog

Shai is the co-founder of Codename One. He's been a professional programmer for over 25 years. During that time he has worked with dozens of companies including Sun Microsystems.
For more follow Shai on Twitter & github.