Is Dalvik's memory model the same as Java's?

Asked 3/1, 2011 at 20:28 Answered 6/1, 2011 at 1:2

Solved java android dalvik memory-model java-memory-model

Is Dalvik's memory model the same as Java's? I am particularly interested in whether reads and writes of reference and non-long/non-double primitive variables are atomic, but I would also like to know whether there are any differences between the two platforms' memory models.

Hitherto answered 3/1, 2011 at 20:28 Comment(0)

As of 4.0 (Ice Cream Sandwich), Dalvik's behavior should match up with JSR-133 (the Java Memory Model).

As of 3.0 (Honeycomb), most of the pieces were in place, but some minor things had been overlooked that would be difficult to encounter in practice (e.g. some edge cases in finalization).

As of 2.3 (Gingerbread), Dalvik was generally correct on uniprocessors, but some key features required for proper behavior on SMP hardware (e.g. proper final field handling) was missing.

Pre-Gingerbread, there were no memory barriers at all, and basic stuff like volatile long was broken.

Duster answered 6/1, 2011 at 1:2 Comment(3)

Vaguely related: Android+SMP Primer at developer.android.com/training/articles/smp.html – Duster 3/12, 2012 at 22:16

The SMP primer above is a must read for anyone dealing with memory shared between threads. Thanks so much for linking this! – Lardaceous 21/1, 2014 at 21:34

@Duster what about double check locking with volatile fix? like described here en.wikipedia.org/wiki/Double-checked_locking#Usage_in_Java will it work on Android? Any version? Will it work on ART? – Boote 17/9, 2014 at 17:6

There is a document in the Dalvik source which says:

From the point of view of a piece of code written in the Java programming language or targeted in the same way to .class files, the Dalvik VM aims to behave in a way that is fully consistent with the language's definition. That is, the code running in Dalvik will behave the same as it would have running in any other virtual machine.

Which should mean that the behaviour is the same as in proper Java. Whether it actually is or not, i have no idea.

Bolzano answered 3/1, 2011 at 21:7 Comment(0)

The specification says that all operations on 32 bit numbers (the non-double, non-long numbers) are atomic. There is no guarantee that operations on 64 bit numbers are atomic as well.

Folse answered 3/1, 2011 at 20:43 Comment(1)

Which specification is this? If you mean the Java specification, i think the point of the question is to ask whether Dalvik implements that part of Java's semantics. If you mean some other specification, nny chance of a link? – Bolzano 3/1, 2011 at 21:1

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