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From Cliff Woolley <cliffwool...@yahoo.com>
Subject memory allocation (was Re: mod_include performance numbers)
Date Sat, 21 Apr 2001 17:39:48 GMT
On Sat, 21 Apr 2001, Greg Ames wrote:

> are you thinking about an atomic push/pop block allocator?  I'll be
> happy to help out if so, especially with the machine instruction level
> stuff.

Yes, I am, and I definitely *will* need help from various people getting
the appropriate machine language magic for their platforms working.  I've
already done the generic fallback locking implementation of the stack;
that was simple.  And I have what you and Jeff gave me for S390.  But...

> yeah, but that stuff can go away.  compare-and-exchange (or compare &
> swap, or load & reserve, or...) is our friend in multithreaded systems,
> especially on multiprocessors.  The piece I haven't figured out is how
> to set up CPU architecture dependent directories, or macros, or
> whatever, in APR.  <sigh>

THAT's the problem.  No other piece of APR is *architecture* dependent.
There's an "arch" include directory, but it's really a misnamed "os"
directory.  I've got a scheme implemented that gives us an APR_ARCH_IS_foo
macro, but it's a hack.  It disobeys the typical APR rule of "all macros
are always defined and have a value of 0 or 1" and is just defined or not.
I've also been afraid that some of the possible ways to implement these
machine-language tricks will also be *compiler* dependent, not just
architecture dependent.  If so, then that makes this that much harder.
For example, I've taken your jstack.h and pulled out the __cds() "calls"
and wrapped a macro around them so that different architectures can insert
their equivalent instruction.  But are "__cds()" and "cds_t" available on
all S390 platforms?  I'm guessing no.  Ugh.  If anybody has a clean way to
do this, I'm all ears.

--Cliff

--------------------------------------------------------------
   Cliff Woolley
   cliffwoolley@yahoo.com
   Charlottesville, VA



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