#980: [PATCH]: GC Refactor
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Reporter: jrtayloriv | Type: patch
Status: new | Priority: minor
Milestone: | Component: GC
Version: 1.5.0 | Severity: low
Keywords: | Lang:
Patch: new | Platform: all
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Attached is a patch which does some minor refactoring of the GC system.
Most of my changes are in an attempt to get closer to being able to choose
our GC system with a command line switch, instead of having to choose it
at compile time.
This is a very rough patch, but I'd like to get some feedback on the
concepts behind it to see if you all think the changes are appropriate,
and then perhaps create a branch to do a lot more work on it. Currently
it is passing all tests on x86-64 Linux.
For starters, I have done the following:
1) I have gotten rid of all of the #if directives (PARROT_GC_MS,
PARROT_GC_GMS, etc) related to selecting the GC system. I have moved this
stuff into system-specific header files (i.e. src/gc/generational_ms.h),
or wherever was appropriate. I have defined a macro PARROT_GC_DEFAULT_SYS
(currently set to 'MS') in include/parrot/settings.h, which will be used
to represent the default GC system (i.e. the one that's used if no --gc
command line switch is passed).
2) I added a GC_subsystem struct * gc_sys to the Parrot_Interp struct.
This structure will contain all data structures and functions (via
function pointers) related specifically to the current GC subsystem we are
using.
3) I have also started to add something similar to GC_Subsytem to the
Small_Object_Pool structure, which was having adding fields added based on
preprocessor directives. At the moment, is is just a union
(gc_sys_private_data) which contains special data structures related to
the Small_Object_Pool for the GC subsystems that need them, but
ultimately, I'm going to make it look like the gc_sys struct (where it
also contains function hooks related to pools such as add_free_object,
etc). And I will do the same for Arenas....
4) Started converting macros like GC_WRITE_BARRIER into proper functions.
These functions will be registered as hooks by assigning functions to the
function pointers stored in the gc_sys structure. A GC subsystem can
register to use these hooks only if they are needed, relieving us of the
need to use preprocessor directives to make this decision.
5) On recommendation from WhiteKnight++ I also created API functions
Parrot_gc_write_barrier() and Parrot_gc_write_barrier_key() in src/api.c
to access the write_barrier hooks in interp->gc_sys, so that nobody has to
go poking around in the internals of the interp structure to use them.
Some things I want to do in the (very near) future are:
1) do further cleanup on the Arenas and Small_Object_Pool structures, and
many other things
2) Move more system-specific functions out of places like api.c and and
into the gc_sys structure
3) Create a command line switch --gc or --gc_sys or whatever, and set it
up to
4) Try to find a way to untangle GMS from the entire Parrot internals ...
and begin designing a new GMS system from scratch that is better
encapsulated.
Anyhow, I am not a very strong C programmer, so there were a view areas
where I ran into problems, and just fudged to get things working. A more
experienced programmer could probably immediately figure out what to do,
in these cases. Namely:
1) My PObj_to_Arena/Arena_to_PObj hooks in gc_sys are not correct (these
don't really matter right now, since they're GMS only anyway though)
2) I've left tons of broken stuff related to GMS commented out. These
things were broken before I did anything to them, but now we actually have
to deal with them since they're not in preprocessor statements anymore,
and I probably broke them a bit more :)
3) I didn't know how I should die if the switch statement in
src/gc/api::Parrot_gc_initialize() reaches it's default case.
4) I wasn't sure exactly how to tell headerizer about the type signatures
of Parrot_gc_write_barrier() and Parrot_gc_write_barrier_key() in
src/api.c
I welcome any comments/suggestions on this.
Attached is the 'svn diff' patch, and the extra file that I created
(src/gc/generational_ms.h). (Sorry, couldn't figure out how to make 'svn
diff' output the contents of the new file as well)
--Jesse
--
Ticket URL: <https://trac.parrot.org/parrot/ticket/980>
Parrot <https://trac.parrot.org/parrot/>
Parrot Development
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