.. 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/1.116/design/abq.txt#1 $ :Copyright: See section `Copyright and License`_. :Index terms: pair: fixed-length queues; design 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 (*ABQVisitor)(Bool *deleteReturn, void *element, void *closure)`` A callback function for ``ABQIterate()``. The parameter ``element`` is an element in the queue, and ``closure`` is the value 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, ABQVisitor visitor, void *closure)`` Call ``visitor`` for each element in the queue, passing the element and ``closure``. See ``ABQVisitor`` for details. Document History ---------------- - 2013-05-20 GDR_ Created. .. _GDR: http://www.ravenbrook.com/consultants/gdr/ Copyright and License --------------------- Copyright © 2013-2016 Ravenbrook Limited . All rights reserved. This is an open source license. Contact Ravenbrook for commercial licensing options. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: #. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. #. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. #. Redistributions in any form must be accompanied by information on how to obtain complete source code for this software and any accompanying software that uses this software. The source code must either be included in the distribution or be available for no more than the cost of distribution plus a nominal fee, and must be freely redistributable under reasonable conditions. For an executable file, complete source code means the source code for all modules it contains. 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