Ravenbrook / Projects / Memory Pool System / Version 1.111 Product Sources / Design Documents

Memory Pool System Project

                         THE DESIGN OF THE ROOT MANAGER
                                design.mps.root
                               incomplete design
                               richard 1995-08-25

    INTRODUCTION

    .intro:

    .readership:

    BASICS

    .root.def: The root node of the object graph is the node which defines whether
    objects are accessible, and the place from which the mutator acts to change the
    graph.  In the MPS, a root is an object which describes part of the root node.
    The root node is the total of all the roots attached to the space.  [Note that
    this combines two definitions of root: the accessibility is what defines a root
    for tracing (see analysis.tracer.root.* and the mutator action for barriers
    (see analysis.async-gc.root).  pekka 1998-03-20]

    .root.repr: Functionally, roots are defined by their scanning functions.  Roots
    _could_ be represented as function closures, i.e. a pointer to a C function and
    some auxiliary fields.  The most general variant of roots is just that.
    However, for reasons of efficiency, some special variants are separated out.

    DETAILS

    Creation

    .create: A root becomes "active" as soon as it is created.

    .create.col: The root inherits its colour from the mutator, since it can only
    contain references copied there by the mutator from somewhere else.  If the
    mutator is grey for a trace when a root is created then that root will be used
    to determine accessibility for that trace.  More specifically, the root will be
    scanned when that trace flips.

    Destruction

    .destroy: It's OK to destroy a root at any time, except perhaps concurrently
    with scanning it, but that's prevented by the arena lock.  If a root is
    destroyed the references in it become invalid and unusable.

    Invariants

    .inv.white: Roots are never white for any trace, because they cannot be
    condemned.

    .inv.rank: Roots always have a single rank.  A root without ranks would be a
    root without references, which would be pointless.  The tracer doesn't support
    multiple ranks in a single colour.

    Scanning

    .method: Root scanning methods are provided by the client so that the MPS can
    locate and scan the root set.  See protocol.mps.root for details.  [There are
    some more notes about root methods in meeting.qa.1996-10-16.]

## A. References

## B. Document History

2002-06-07 | RB | Converted from MMInfo database design document.

## C. Copyright and License

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