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Diff for /OpenXM_contrib/gc/Attic/README between version 1.1.1.1 and 1.1.1.2

version 1.1.1.1, 1999/11/27 10:58:32

version 1.1.1.2, 2000/04/14 11:08:01

Line 1

THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED

OR IMPLIED. ANY USE IS AT YOUR OWN RISK.

Line 11 Permission to modify the code and to distribute modifi

Line 12 Permission to modify the code and to distribute modifi

provided the above notices are retained, and a notice that the code was

modified is included with the above copyright notice.

This is version 4.14 of a conservative garbage collector for C and C++.

This is version 5.0alpha4 of a conservative garbage collector for C and C++.

You might find a more recent version of this at

http://reality.sgi.com/boehm/gc.html

http://www.hpl.hp.com/personal/Hans_Boehm/gc

HISTORY -

Early versions of this collector were developed as a part of research

projects supported in part by the National Science Foundation

and the Defense Advance Research Projects Agency.

Much of the code was rewritten by Hans-J. Boehm at Xerox PARC

Much of the code was rewritten by Hans-J. Boehm (boehm@acm.org) at Xerox PARC

and is now maintained by him at SGI (boehm@sgi.com).

and at SGI.

Some other contributors:

Line 40 Robert Brazile (brazile@diamond.bbn.com) originally su

Line 41 Robert Brazile (brazile@diamond.bbn.com) originally su

Al Dosser (dosser@src.dec.com) and Regis Cridlig (Regis.Cridlig@cl.cam.ac.uk)

subsequently provided updates and information on variation between ULTRIX

systems. Parag Patel (parag@netcom.com) supplied the A/UX code.

Jesper Peterson(jep@mtiame.mtia.oz.au) and

Jesper Peterson(jep@mtiame.mtia.oz.au), Michel Schinz, and

Michel Schinz supplied the Amiga port.

Martin Tauchmann (martintauchmann@bigfoot.com) supplied the Amiga port.

Thomas Funke (thf@zelator.in-berlin.de(?)) and

Brian D.Carlstrom (bdc@clark.lcs.mit.edu) supplied the NeXT ports.

Douglas Steel (doug@wg.icl.co.uk) provided ICL DRS6000 code.

Line 612 reclaimed. Exclusive-or'ing forward and backward link

Line 613 reclaimed. Exclusive-or'ing forward and backward link

doesn't cut it.

Some C optimizers may lose the last undisguised pointer to a memory

object as a consequence of clever optimizations. This has almost

never been observed in practice. Send mail to boehm@sgi.com

never been observed in practice. Send mail to boehm@acm.org

for suggestions on how to fix your compiler.

This is not a real-time collector. In the standard configuration,

percentage of time required for collection should be constant across

Line 621 heap sizes. But collection pauses will increase for l

Line 622 heap sizes. But collection pauses will increase for l

per MB of accessible memory that needs to be scanned. Your mileage

may vary.) The incremental/generational collection facility helps,

but is portable only if "stubborn" allocation is used.

Please address bug reports to boehm@sgi.com. If you are

Please address bug reports to boehm@acm.org. If you are

contemplating a major addition, you might also send mail to ask whether

it's already been done (or whether we tried and discarded it).

Line 1451 Since 4.14alpha1

Line 1452 Since 4.14alpha1

Since 4.14alpha2

- changed STACKBOTTOM for DJGPP (Thanks to Salvador Eduardo Tropea).

Since 4.14

- Reworked large block allocator. Now uses multiple doubly linked free

lists to approximate best fit.

- Changed heap expansion heuristic. Entirely free blocks are no longer

counted towards the heap size. This seems to have a major impact on

heap size stability; the old version could expand the heap way too

much in the presence of large block fragmentation.

- added -DGC_ASSERTIONS and some simple assertions inside the collector.

This is mainlyt for collector debugging.

- added -DUSE_MUNMAP to allow the heap to shrink. Suupported on only

a few UNIX-like platforms for now.

- added GC_dump_regions() for debugging of fragmentation issues.

- Changed PowerPC pointer alignment under Linux to 4. (This needs

checking by someone who has one. The suggestions came to me via a

rather circuitous path.)

- Changed the Linux/Alpha port to walk the data segment backwards until

it encounters a SIGSEGV. The old way to find the start of the data

segment broke with a recent release.

- cordxtra.c needed to call GC_REGISTER_FINALIZER instead of

GC_register_finalizer, so that it would continue to work with GC_DEBUG.

- allochblk sometimes cleared the wrong block for debugging purposes

when it dropped blacklisted blocks. This could result in spurious

error reports with GC_DEBUG.

- added MACOS X Server support. (Thanks to Andrew Stone.)

- Changed the Solaris threads code to ignore stack limits > 8 MB with

a warning. Empirically, it is not safe to access arbitrary pages

in such large stacks. And the dirty bit implementation does not

guarantee that none of them will be accessed.

- Integrated Martin Tauchmann's Amiga changes.

- Integrated James Dominy's OpenBSD/SPARC port.

Since 5.0alpha1

- Fixed bugs introduced in alpha1 (OpenBSD & large block initialization).

- Added -DKEEP_BACK_PTRS and backptr.h interface. (The implementation

idea came from Al Demers.)

Since 5.0alpha2

- Added some highly incomplete code to support a copied young generation.

Comments on nursery.h are appreciated.

- Changed -DFIND_LEAK, -DJAVA_FINALIZATION, and -DFINALIZE_ON_DEMAND,

so the same effect could be obtained with a runtime switch. This is

a step towards standardizing on a single dynamic GC library.

- Significantly changed the way leak detection is handled, as a consequence

of the above.

Since 5.0 alpha3

- Added protection fault handling patch for Linux/M68K from Fergus

Henderson and Roman Hodek.

- Removed the tests for SGI_SOURCE in new_gc_alloc.h. This was causing that

interface to fail on nonSGI platforms.

- Changed the Linux stack finding code to use /proc, after chnging it

to use HEURISTIC1. (Thanks to David Mossberger for pointing out the

/proc hook.)

- Added HP/UX incremental GC support and HP/UX 11 thread support.

- Added basic Linux/IA64 support.

- Integrated Anthony Green's PicoJava support.

- Integrated Scott Ananian's StrongARM/NetBSD support.

- Fixed some fairly serious performance bugs in the incremental

collector. These have probably been there essentially forever.

(Mark bits were sometimes set before scanning dirty pages.

The reclaim phase unnecessarily dirtied full small object pages.)

- Changed the reclaim phase to ignore nearly full pages to avoid

touching them.

- Limited GC_black_list_spacing to roughly the heap growth increment.

- Changed full collection triggering heuristic to decrease full GC

frequency by default, but to explicitly trigger full GCs during

heap growth. This doesn't always improve things, but on average it's

probably a win.

- GC_debug_free(0, ...) failed. Thanks to Fergus Henderson for the

bug report and fix.

To do:

- Very large root set sizes (> 16 MB or so) could cause the collector

to abort with an unexpected mark stack overflow. (Thanks again to

Line 1465 To do:

Line 1537 To do:

be possible to conditionally intercept mmap and use GC_exclude_static_roots.

The real fix is to walk rld data structures, which looks possible.

- Integrate MIT and DEC pthreads ports.

- Deal with very uneven black-listing distributions. If all the black listed

- Incremental collector should handle large objects better. Currently,

blocks reside in the newly allocated heap section, the heuristic for

it looks like the whole object is treated as dirty if any part of it

temporarily ignoring black-listing fails, and the heap grows too much.

is.

(This was observed in only one case, and could be worked around, but ...)

- I've started work on rewriting the large block allocator to use approximate

best fit. There are rare cases in which the current allocator results in

excessive large block fragmentation, even with the 4.13 fixes. This should

also reduce large block allocation time, whcih has become occasionally

noticable in 4.13.

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