Dukeleto asked me to put together a general timeline or checklist of changes that we need to make to Parrot, organized by size and scope of the work, the effort required, and the relative ordering that (I think) is a pretty good way to go about it.
This isn't an "official" timeline or anything like that. It's just my own personal idea for what we should probably be doing, and how hard it will be to do. The items below are listed in a quasi-chronological order in the sense that, left to my own devices, I will probably approach these problems myself in this order. Other people are welcome to tackle things in any order, so long as dependencies are met.
- Extent of change: small
- Effort required: moderate
- Relative priority: moderate
We need to convert our GC to be precise. We have some good ideas floating around for how to do that, and implementation of the code won't be hard. What will be challenging is tracking down places where PMCs are used on the stack and converting those to use a new API/macro to be anchored. This could have a positive impact on performance and will help make things more thread-safe when we get to tasks that require that.
- Upgrade effort for HLLs: minor (fixes to C code)
- Benefits for HLLs: Better GC performance
- Extent of change: large
- Effort required: large
- Relative priority: large
See my blog post about the problem with Subs for examples:
http://whiteknight.github.com/2011/08/15/sub_problems.html
We need to rip a hell of a lot of stuff out of the Sub PMC, make IMCC smarter about how it serializes some things (like NameSpaces and MultiSubs) and make the packfile loader a hell of a lot smarter about how things get unpacked. Fix NameSpace to not be terrible. Remove all sorts of extra PIR flags like :nsentry, :anon, :multi, etc.
This is a very big project, but represents an extremely central portion of Parrot. User code is going to be forced to pick up the slack from all the magic we're going to be removing from key systems. This is going to require changes to Winxed and NQP to keep code working.
- Upgrade effort for HLLs: Need to change code generation to avoid using removed flags. Need to generate code to explicitly add Subs to NameSpaces or to MultiSubs if desired.
- Benefits for HLLs: Improved packfile loading performance. Improved NameSpace PMC performance. Decreased binary code size overall. Better control over how Sub PMCs are used and stored in the system.
- Extent of change: moderate
- Effort required: high
- Relative priority: moderate
See my blog post series about redoing PCC (first is most important):
http://whiteknight.github.com/2011/05/11/pcc_refactors_and_improvements.html http://whiteknight.github.com/2011/05/10/timings_vtable_overrides.html http://whiteknight.github.com/2011/05/12/pcc_refactor_timings.html
We need to replace the get_params, set_args, set_returns and get_results ops with a fast way to access the current CallContext and specialized ops for reading named/positional values from the context. We have most of the ops we would need already. What we don't have yet are the necessary slice/splice ops for doing :slurpy and :slurpy/:named.
There are real performance benefits to be had. This change is going to primarily require changes to IMCC to generate new sequences of ops. It could lead to some significant improvements there. User code that uses PIR syntax for sub/method calls and .param syntax for parameters should be safe. Lots of tests written in PASM are going to die.
- Upgrade effort for HLLs: None (changes are internal to IMCC only)
- Benefits for HLLs: Improved invoke performance for all PIR->PIR calls. Improved performance for generating backtraces. Easier to build tools like debuggers and static analyzers. Improved PBC disassembly potential. Ability to fetch parameters lazily.
-
Extent of change: low
-
Effort required: moderate
-
Relative priority: moderate
-
Upgrade effort for HLLs: none.
-
Benefits for HLLs: New tools for debugging and analysis, and the possibility to make more new custom tools.
- Extent of change: low
- Effort required: low
- Relative priority: high
I've got a few ideas about how to implement basic sandboxing that need to be blogged about more, designed, and prototyped.
- Upgrade effort for HLLs: minor (PIR code and above will be unchanged. Some C-level APIs will change. New sandboxing/security standards will need to be followed internally.)
- Benefits for HLLs: Addition of basic sandboxing and security features.
- Extent of change: large
- Effort required: large
- Relative priority: high
Need to merge 6model ideas into the Parrot object model at the ground up. Need to completely redo some fundamental parts of the system, such as PMCs, type bootstrapping at startup, vtables, etc.
- Upgrade effort for HLLs: Unknown/variable. The first attempt will try to be compatible at C and PIR levels with the 6model version being used in NQP. NQP will need to be changed to use the version built-in to Parrot instead of building and linking its own. Languages running on NQP should be mostly unaffected.
- Benefits for HLLs: Better overall performance of objects and data operations, especially as integration improves. Far better interoperability between 6model and Class/Object for systems that want to use both. Possibly improved libparrot startup time.
- Extent of change: high
- Effort required: moderate
- Relative priority: high
See some blog posts on the subject:
http://whiteknight.github.com/2011/01/26/exception_handler_redux.html http://whiteknight.github.com/2010/02/24/pdd23_exceptions_critique.html http://whiteknight.github.com/2010/02/23/parrots_exceptions_system.html
The exceptions subsystem is a mess and needs to be re-thought. We need to remove the scheduler from the lookup for handlers. We need a lot of stuff, and need to keep a close eye on performance, especially if exceptions are going to continue to be used for normal control flow.
- Upgrade effort for HLLs: none (first wave of changes are internal only)
- Benefits for HLLs: Better performance for exceptions and handlers. Possibly better able to use custom subclasses for both.
-
Extent of change: moderate
-
Effort required: low
-
Relative priority: high
-
Upgrade effort for HLLs: Minor (some C code which pokes into Interp* directly will need to be changed. PIR code should be unaffected)
-
Benefits for HLLs: Nothing immediate
-
Extent of change: moderate
-
Effort required: moderate
-
Relative priority: moderate
-
Upgrade effort for HLLs: None (unless you are using threads, or are relying on vestigial C-level details of the threading system)
-
Benefits for HLLs: Modest performance improvements. Improved security and separation between interps at the C level.
-
Extent of change: low
-
Effort required: moderate
-
Relative priority: low
-
Upgrade effort for HLLs: None (but can add AIO features as desired)
-
Benefits for HLLs: new IO features
- Extent of change: large
- Effort required: moderate
- Relative priority: low
We need to stop referring to Class objects by string name. Not all of them can be stringified and some classes aren't known at compile time. We need to be able to associate a Sub with more than one multi sigs (which means not storing multi_sig in the Sub PMC). We need to create Multis at compile time or at load time in user :load subs, not in the packfile loader.
We need to expand MMD to be able to handle the full range of PCC capabilities. We should be able to specify :optional/:opt_flag, :slurpy, and :named varieties in multisigs so we can make more intelligent dispatches.
We should be smarter about lookups and cacheing. We probably would like to move to a DAG to search for candidates, or something better than an in-place manhattan sort. We would probably like to do some kind of call-site caching, although that may want to wait until JIT.
In short, the system needs to be redone from the ground up.
- Upgrade effort for HLLs: If you are using Parrot's MMD from PIR code, you will need to write code to add Subs to MultiSubs explicitly. If you are using NQP or Winxed, those code generators will be updated to do the right thing. If you are not using Parrot's built-in MMD, you will be unaffected
- Benefits for HLLs: Better performance of MMD system. More feature-full default MMD system. More control over how Subs are associated with signatures. The ability to use Subs with more than one signature without cloning.
Details to come.
-
Extent of change: moderate
-
Effort required: moderate
-
Relative priority: low
-
Upgrade effort for HLLs: Unknown. New interface may be same, old interface may be kept for backwards compatibility. Additional PIR (or new ops) might need to be generated for exception throw and catch. The basic common case should probably be unchanged.
-
Benefits for HLLs: Improved control over exception dispatch. Improved ability to subclass Exception and ExceptionHandler. Ability to use features like MMD with exception dispatch. Simplified exception resume.
This is a really nice write-up!