.. mode: -*- rst -*- Fixed-length queues =================== :Tag: design.mps.abq :Author: Gareth Rees :Date: 2013-05-20 :Status: complete design :Revision: $Id: //info.ravenbrook.com/project/mps/version/1.114/design/abq.txt#1 $ :Copyright: See section `Copyright and License`_. Introduction ------------ _`.intro`: This is the design of the ABQ module, which implements a fixed-length queue of small objects. _`.readership`: This document is intended for any MM developer. _`.name`: The name ABQ originally stood for "Available Block Queue" as the module is used by the MVT pool. Requirements ------------ _`.req.push`: Clients can efficiently push new elements onto the queue. _`.req.pop`: Clients can efficiently pop elements from the queue. _`.req.empty`: Clients can efficiently test whether the queue is empty. _`.req.abstract`: The ABQ module does not know anything about the elements in the queue other than their size. _`.req.delete`: Clients can delete elements from the queue. (Note: not necessarily efficiently.) _`.req.iterate`: Clients can iterate over elements in the queue. Interface --------- ``typedef ABQStruct *ABQ`` ``ABQ`` is the type of a queue. It is an alias for ``ABQStruct *``. ``ABQStruct`` is defined in the header so that it can be inlined in client structures: clients must not depend on its implementation details. ``ABQInit(Arena arena, ABQ abq, void *owner, Count elements, Size elementSize)`` Initialize the queue ``abq``. The parameter ``arena`` is the arena whose control pool should be used to allocate the memory for the queue; ``owner`` is passed to ``MeterInit()`` for the statistics; ``elements`` is the maximum number of elements that can be stored in the queue; and ``elementSize`` is the size of each element. ``void ABQFinish(Arena arena, ABQ abq)`` Finish ``abq`` and free all resources associated with it. ``Bool ABQPush(ABQ abq, void *element)`` If the queue is full, leave it unchanged and return ``FALSE``. Otherwise, push ``element`` on to the queue and return ``TRUE``. ``Bool ABQPop(ABQ abq, void *elementReturn)`` If the queue is empty, return ``FALSE``. Otherwise, copy the first element on the queue into the memory pointed to by ``elementReturn``, remove the element from the queue, and return ``TRUE``. ``Bool ABQPeek(ABQ abq, void *elementReturn)`` If the queue is empty, return ``FALSE``. Otherwise, copy the first element on the queue into the memory pointed to by ``elementReturn`` and return ``TRUE``. (This is the same as ``ABQPop()`` except that the queue is unchanged.) ``Bool ABQIsEmpty(ABQ abq)`` If the queue is empty, return ``TRUE``, otherwise return ``FALSE``. ``Bool ABQIsFull(ABQ abq)`` If the queue is full, return ``TRUE``, otherwise return ``FALSE``. ``Count ABQDepth(ABQ abq)`` Return the number of elements in the queue. ``typedef Bool (*ABQIterateMethod)(Bool *deleteReturn, void *element, void *closureP, Size closureS)`` A callback function for ``ABQIterate()``. The parameter ``element`` is an element in the queue, and ``closureP`` and ``closureS`` are the values that were originally passed to ``ABQIterate()``. This function must set ``*deleteReturn`` to ``FALSE`` if ``element`` must be kept in the queue, or ``TRUE`` if ``element`` must be deleted from the queue. It must return ``TRUE`` if the iteration must continue, or ``FALSE`` if the iteration must stop after processing ``element``. ``void ABQIterate(ABQ abq, ABQIterateMethod iterate, void *closureP, Size closureS)`` Call ``iterate`` for each elements in the queue, passing the element and ``closureP``. See ``ABQIterateMethod`` for details. Document History ---------------- - 2013-05-20 GDR_ Created. .. _GDR: http://www.ravenbrook.com/consultants/gdr/ Copyright and License --------------------- Copyright © 2013-2014 Ravenbrook Limited. All rights reserved. . This is an open source license. Contact Ravenbrook for commercial licensing options. 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