Re: [CZT-Devel] Memory allocation with ArrayLists

[Leo F. <leo...@ne...>]

Hi Tim,

That's interesting. I';ve been doing similar (profiling) tests over specs of some size (e.g., Mondex, Tokeneer, Xenon, IEEE float point unit); 
although I guess they are smaller than iFACTS - apart from Xenon, which is quite large.

On the profiling sessions, the worst culprit was "char[]" arrays, mostly from the java_cup lexer. The Object[] and ArrayList[] were about 2-3% each,
for what the char[] was 90% (!)... Similarly, on profiling CPU, it was the IO operations on zzRefill within the java_cup scanner that took the largest chunk
of the time (27%). Smart scanning (e.g., lookahead) has taken only about 2-3%. 

I wonder... what was the profilling setup that you used to get to the creation of Object[] ArrayList as the main problem?
Although the change you refer to below shouldn't be relatively simple to change, as Petra pointed out. 

I just want to get the right picture to tackle such performance problem for larger specs.

Best,
Leo

On 5 Jan 2012, at 23:51, Tim Miller wrote:

> Hi everyone,
> 
> Anthony Hall and I have been discussing some memory problems that CZT 
> has when parsing large specifications. Anthony has been trying to 
> typecheck the iFacts specification, but without much luck due to the 
> large memory resources.
> 
> We've each been playing around with VisualVM, and Anthony pointed out is 
> that the two largest memory hogs are Object[] and ArrayList, taking up 
> around 23% and 10% of the heap respectively.
> Most of the object arrays and ArrayLists contain exactly 10 items, and 
> almost all items in these lists are null.
> 
> After some poking around, I discovered that when ArrayList is created 
> using the default constructor, it allocates 10 items initially. This 
> appears to be where the 10 items come from in each case. I suspect this 
> may also be contributing to some of the memory problems, considering 
> that CZT has so many empty annotation lists, etc. Creating ArrayLists 
> with an initial capacity of 0 or 1 (using the constructor ArrayList(int 
> initialCapacity)) may give us some substantial space savings
> 
> It appears that most ArrayLists are created in the gnast-generated code. 
> Petra, how difficult would it be to create these lists using this other 
> constructor?
> 
> Regards,
> Tim
> 
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