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<link rel="shortcut icon" href="../rho.ico">
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<title>Write your own InterlockedXxx
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operation</title> </head> <body>
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<p><A href="./"> To Home page</A> </p>
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<h1>Write your own InterlockedXxx
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operation</h1><p>
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It has long been known that InterlockedCompareExchange can be
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used to write any Interlockedxxx operation. </p>
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<pre>
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long InterlockedXxx(
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__inout long volatile *Target,
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, whatever parameters we need for Xxx
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)
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{
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long prevValue, prevCopy;
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prevValue = *Target;
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2022-02-18 15:59:12 -05:00
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do {
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if Xxx operations is illegal on prevValue, return with error code
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2022-02-18 15:59:12 -05:00
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prevCopy = prevValue;
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//
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// prevValue will be the value that used to be Target if the exchange was made
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// or its current value if the exchange was not made.
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//
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prevValue = InterlockedCompareExchange(Target, Xxx operation on prevCopy, prevValue);
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//
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// If prevCopy == prevValue, then no one updated Target in between the deref at the top
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// and the InterlockecCompareExchange afterward and we are done
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//
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} while (prevCopy != prevValue);
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//
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// [value] can be anything you want, but it is typically either
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// a) The new value stored in Target. This is the type of return value that
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// InterlockedIncrement returns
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// or
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// b) The new value is the previous value that was in Target. This si the
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// type of return value that InterlockedOr or InterlockedExchange return
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//
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return [value];
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}</pre><p>
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Structures larger than a long can be handled by
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using InterlockedCompareExchange to add to a
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linked list, or remove stuff from a linked
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list. Of course you should not be writing such
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things yourself, when Intel has already written
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it for you. </p>
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<p style="background-color : #ccffcc; font-size:80%">These documents are
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licensed under the <a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/">Creative
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Commons Attribution-Share Alike 3.0 License</a></p>
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</body></html>
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