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copied!<p>I don't know of any lock-free (or micro-locking as in your example above) MREW approach that could be implemented on Intel86 code.</p> <p>For small (fast-expiring) locks a spinning approach from the <a href="http://code.google.com/p/omnithreadlibrary/source/browse/branches/fast-notifications/OtlSync.pas" rel="noreferrer">OmniThreadLibrary</a> works fine:</p> <pre><code>type TOmniMREW = record strict private omrewReference: integer; //Reference.Bit0 is 'writing in progress' flag public procedure EnterReadLock; inline; procedure EnterWriteLock; inline; procedure ExitReadLock; inline; procedure ExitWriteLock; inline; end; { TOmniMREW } procedure TOmniMREW.EnterReadLock; var currentReference: integer; begin //Wait on writer to reset write flag so Reference.Bit0 must be 0 than increase Reference repeat currentReference := omrewReference AND NOT 1; until currentReference = InterlockedCompareExchange(omrewReference, currentReference + 2, currentReference); end; { TOmniMREW.EnterReadLock } procedure TOmniMREW.EnterWriteLock; var currentReference: integer; begin //Wait on writer to reset write flag so omrewReference.Bit0 must be 0 then set omrewReference.Bit0 repeat currentReference := omrewReference AND NOT 1; until currentReference = InterlockedCompareExchange(omrewReference, currentReference + 1, currentReference); //Now wait on all readers repeat until omrewReference = 1; end; { TOmniMREW.EnterWriteLock } procedure TOmniMREW.ExitReadLock; begin //Decrease omrewReference InterlockedExchangeAdd(omrewReference, -2); end; { TOmniMREW.ExitReadLock } procedure TOmniMREW.ExitWriteLock; begin omrewReference := 0; end; { TOmniMREW.ExitWriteLock } </code></pre> <p>I just noticed a possible alignment issue here - the code should check that omrewReference is 4-aligned. Will notify the author.</p>

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