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From: Eliot Miranda <eliot.miranda@gmail.com> Date: August 17, 2009 8:09:25 PM CEDT To: Henrik Johansen <henrik.s.johansen@veloxit.no> Cc: Stéphane Ducasse <stephane.ducasse@inria.fr>, Marcus Denker <denker@acm.org

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, John McIntosh <johnmci@smalltalkconsulting.com> Subject: Re: [Pharo-project] SequenceableCollection do: causes GCs with closure bytecodes

On Mon, Aug 17, 2009 at 7:02 AM, Stéphane Ducasse <stephane.ducasse@inria.fr

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wrote:

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From: Henrik Johansen <henrik.s.johansen@veloxit.no> Date: August 17, 2009 3:21:53 PM CEDT To: Pharo-project@lists.gforge.inria.fr Subject: [Pharo-project] SequenceableCollection do: causes GCs with closure bytecodes Reply-To: Pharo-project@lists.gforge.inria.fr

Something I noticed when looking at ByteArray>>hex, anyone know the reason why there's GC going on in do: with closure images, but not using the old bytecodes?

Because with the old bytecodes a block activation simply reuses the BlockContext allocated to implement the block whereas with the new bytecodes a block activation allocates a new context. The stack VM reduces context allocation markedly and so simple examples like the below won't allocate. In the stack VM context allocation is deferred until the context object is actually used. Contexts are allocated on process switch, when a block is created or when thisContext is used.

HTH

Even with no closed-over variables in the block, it seems it creates extra fodder for the Garbage collector...

Is it something the stack VM / Improved Garbage Collector will change?

Cheers, Henry

Simple test: intArray := (1 to: 10000000) asArray. TimeProfileBrowser onBlock: [intArray do: [:ix | ix yourself]] (It's not due to sampling overhead, Time millisecondsToRun: return similiar runtimes)

Without closures (I used 250): -941 tallies, 965 msec. **GCs** incr 4 totalling 0ms

With closures (I used 414): -1938 tallies, 1938 msec. **GCs** inc 2510 totalling 614ms

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