Compile Time Garbage Collection impossible? - Compilers

This is a discussion on Compile Time Garbage Collection impossible? - Compilers ; I think that compile time garbage collection is impossible, and existing approximation are not good enough or scalable. (it is my opinion, but what do I know?) But there have been some success in developing runtime tools to identify and ...

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Compile Time Garbage Collection impossible?

  1. Default Re: Compile Time Garbage Collection impossible?

    I think that compile time garbage collection is impossible, and
    existing approximation are not good enough or scalable. (it is my
    opinion, but what do I know?)

    But there have been some success in developing runtime tools to
    identify and isolate problems due to holding references beyound useful
    life an object. I will list two approaches:

    1. Leakbot at IBM Research : It identifies "leaking regions" in Java
    programs by doing heapdump ****ysis. References can be found at
    http://domino.research.ibm.com/comm/...novation2.html
    and this technology has gone into products such as Rational
    Application Developer
    (http://www.ibm.com/developerworks/ra..._GuptaPalanki/)
    and Memory Dump Diagnostic tool bundled with WebSphare. So this one is
    pretty scalable and useful. I have used with heap dumps from
    production environments having 20+ million objects and almost 39+
    million references.

    2. Tools to identify Lag, Drag, Void and Use of various objects in
    heap: Originally it was done for Haskell (N. Rojemo and C. Runciman,
    "Lag, drag, void and use -- heap profiling and space-efficient
    compilation revisited," Proceedings of the ACM SIGPLAN International
    Conference on Function Programming, pp. 34-41, 1996), and later for
    Java as well (R. Shaham, E. K. Kolodner, and M. Sagiv, "Heap Profiling
    for Space-Efficient Java," Proceedings of ACM SIGPLAN Conference on
    Programming Language Design and Implementation, pp. 104-113, 2001).

    Of course, these tools wouldn't GC the "useless but rechable" objects
    automatically. They just indicate where you need to look to fix your
    program so that a reference to unused objects doesn't remain alive.
    Interestingly, Shaham/Kolodner/Sagiv indicate that the future work
    would be to use the drag ****ysis results for directing static
    ****ysis in a compiler to automatically do some code transformation
    for reducing drag.

    my 2 bits,
    +satish


    --- glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:

    > A.L. wrote:
    >
    > (snip)


    >> Determining what objects could be deallocated during compilation is
    >> equivalent to "halting problem" that is undecidable. i.e. there is
    >> no algorithm possible that could do this for all possible programs.


    > I don't disagree, but determining deallocation at
    > run-time isn't so easy, either.


    > In addition to circular linked lists, which as already mentioned are
    > a problem for reference count GC, there is memory allocated in main
    > and not referenced later. Those two are often indicated in Java
    > documentation. ...



  2. Default Re: Compile Time Garbage Collection impossible?

    the.real.doctor.zoidberg wrote:
    > Why isn't Compile-Time-Garbage-Collection feasible? Consider a Java
    > compiler which produces assembly code for a specific target instead of
    > Java's bytecode cenario. The objective is to use Java without the need
    > for a GC or VM.


    Java sucks nearly every time.

    GC not always.

    Why do you want to avoid GC?

    If you want a language that has GC but nevertheless
    is performant, use OCaml.

    http://www.ocaml-tutorial.org/garbage_collection

    Ciao,
    Oliver

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