Fwd: SequenceableCollection do: causes GCs with closure bytecodes

From: Eliot Miranda <[hidden email]>

Date: August 17, 2009 8:09:25 PM CEDT

To: Henrik Johansen <[hidden email]>

Cc: Stéphane Ducasse <[hidden email]>,  Marcus Denker <[hidden email]>, John McIntosh <[hidden email]>

Subject: Re: [Pharo-project] SequenceableCollection do: causes GCs with  closure bytecodes

On Mon, Aug 17, 2009 at 7:02 AM, Stéphane Ducasse <[hidden email]> wrote:

Begin forwarded message:

From: Henrik Johansen <[hidden email]>
Date: August 17, 2009 3:21:53 PM CEDT
To: [hidden email]
Subject: [Pharo-project] SequenceableCollection do: causes GCs with closure bytecodes
Reply-To: [hidden email]

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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