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timeline.md

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+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.
+
+### GC: Convert to Precise GC
+
+*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.
+
+### Packfiles: Rewrite packfile loading
+
+*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.
+
+### PCC: Redo PIR ops for call conventions
+
+*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.
+
+### Packfiles: Debugging
+
+*Extent of change: low
+*Effort required: moderate
+*Relative priority: moderate
+
+### Interp: Sandboxing
+
+*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.
+
+### OO: 6model
+
+*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. 
+
+### Exceptions: Cleanup and Optimizations
+
+*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.
+
+### Interp: Make Thread-Safe
+
+*Extent of change: moderate
+*Effort required: low
+*Relative priority: high
+
+### Threads: Rip Out and Replace
+
+*Extent of change: moderate
+*Effort required: moderate
+*Relative priority: moderate
+
+### IO: Proper Asynchronous IO
+
+*Extent of change: low
+*Effort required: moderate
+*Relative priority: low
+
+### MMD: Napalm Death
+
+*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.
+
+### Strings: None
+
+### Embedding API: None
+
+### NCI: None