Jan 15, 2021, 6:27:20 PM (9 months ago)
Andrew Beach <ajbeach@…>
arm-eh, jacob/cs343-translation, master, new-ast-unique-expr
0cc43e1, 35ea4f3

Andrew MMath: Added some features and cleaned up future.tex.

1 edited


  • doc/theses/andrew_beach_MMath/future.tex

    r77ff383 r02b73ea  
    88parts of the exception system that use the current version.
    10 For instance a full virtual system would probably allow for several
    11 improvements to the exception traits. Although they do currently work they
    12 could be made easier to use by making the virtual table type implitate in the
    13 trait (which would remove the need for those wrapper marcos) or allowing
    14 for assertions that give the layout of a virtual table for safety.
     10There are several improvements to the virtual system that would improve
     11the exception traits. The biggest one is an assertion that checks that one
     12virtual type is a child of another virtual type. This would capture many of
     13the requirements much more precisely.
     15The full virtual system might also include other improvement like associated
     16types. This is a proposed feature that would allow traits to refer to types
     17not listed in their header. This would allow the exception traits to not
     18refer to the virtual table type explicatly which would remove the need for
     19the interface macros.
    1621\section{Additional Throws}
    6671Also new techniques to skip previously searched parts of the stack will have
    67 to be developed.
     72to be developed. The recursive resume problem still remains and ideally the
     73same pattern of ignoring sections of the stack.
    69 \section{Support for More Platforms}
    70 Termination is not portable because it is implemented with inline assembly.
    71 Those sections will have to be rewritten to support different architectures
     75\section{Signal Exceptions}
     76Exception Handling: Issues and a Proposed Notation suggests there are three
     77types of exceptions: escape, notify and signal.
     78Escape exceptions are our termination exceptions, notify exceptions are
     79resumption exceptions and that leaves signal exception unimplemented.
    73 \section{Quality-of-Life Improvements}
    74 Finally come various improvements to the usability of \CFA. Most of these
    75 would just require time. Time that would not lead to interesting research so
    76 it has been left aside for now. A few examples are included here but there
    77 are more:
     81Signal exceptions allow either behaviour, that is after the exception is
     82handled control can either return to the throw or from where the handler is
     85The design should be rexamined and be updated for \CFA. A very direct
     86translation would perhaps have a new throw and catch pair and a statement
     87(or statements) could be used to decide if the handler returns to the throw
     88or continues where it is, but there are other options.
     90For instance resumption could be extended to cover this use by allowing
     91local control flow out of it. This would require an unwind as part of the
     92transition as there are stack frames that have to be removed.
     93This would mean there is no notify like throw but because \CFA does not have
     94exception signatures a termination can be thrown from any resumption handler
     95already so there are already ways one could try to do this in existing \CFA.
     97% Maybe talk about the escape; and escape CONTROL_STMT; statements or how
     98% if we could choose if _Unwind_Resume proceeded to the clean-up stage this
     99% would be much easier to implement.
     101\section{Language Improvements}
     102There is also a lot of work that are not follow ups to this work in terms of
     103research, some have no interesting research to be done at all, but would
     104improve \CFA as a programming language. The full list of these would
     105naturally be quite extensive but here are a few examples that involve
     109\item The implementation of termination is not portable because it includes
     110some assembly statements. These sections will have to be re-written to so
     111\CFA has full support on more machines.
    80112\item Allowing exception handler to bind the exception to a reference instead
    81113of a pointer. This should actually result in no change in behaviour so there
    88120much easier. (To do the same for try blocks would probably wait for zero-cost
    89121exceptions, which would allow the try block to be inlined as well.)
    90 \item Enabling local control flow out of a resumption handler. This would be
    91 a weighty operation, causing a stack unwind like a termination, so there might
    92 be a different statement or a statement modifier to make sure the user does
    93 this purposefully.
    95 However this would require the more complex system as they cannot be inlined
    96 into the original function as they can be run at a different place on the
    97 stack. So instead the unwinding will have to carry with it information on
    98 which one of these points to continue at and possibly also the return value
    99 for the function if a \codeCFA{return} statement was used.
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