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POFaster TMultiReadExclusiveWriteSynchronizer?
 

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    <p>Is there a <em>faster</em> kind of <code>TMultiReadExclusiveWriteSynchronizer</code> out there? FastCode perhaps?</p> <p>Starting with Windows Vista, Microsoft added a <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa904937%28v=vs.85%29.aspx" rel="nofollow noreferrer">Slim Reader/Writer lock</a>. It <a href="http://blog.delphi-jedi.net/2011/09/16/slim-readwrite-lock-the-fast-alternative-to-tmultireadexclusivewritesynchronizer/" rel="nofollow noreferrer">performs much better</a> than Delphi's <code>TMultiReadExclusiveWriteSynchronizer</code>. Unfortunately it only exists in Windows Vista and later, something which few customers actually have yet.</p> <p>Presumably the concepts in use inside a <code>Slim Reader/Writer lock</code> could be redone in native Delphi code - but has anyone done it?</p> <p>i have a situation where acquiring and releasing locks on a <code>TMultiReadExclusiveWriteSynchronizer</code> (even when there's no contention - a single thread), causes 100% overhead (the operation time doubles). i can run without locking, but then my class is no longer thread-safe.</p> <p>Is there a faster <code>TMultiReadExclusiveWriteSynchronizer</code>?</p> <p><strong>Note</strong>: If i use a <code>TCriticalSection</code> i only suffer a 2% performance hit (although critical sections are known to be fast when the <em>acquire</em> succeeds, i.e. while it's single threaded and there's no contention). The downside of a CS is that i lose the "<em>multiple readers</em>" capability.</p> <h1>The Measurements</h1> <p>Using <code>TMultiReadExclusiveWriteSynchronizer</code> a sizable amount of time is spent inside <code>BeginRead</code> and <code>EndRead</code>:</p> <p><img src="https://i.stack.imgur.com/mPIyZ.png" alt="enter image description here"></p> <p>i then ported the code to use Window's own <strong>SlimReaderWriter Lock</strong> (which some code rewrite, as it doesn't support recursive lock taking), and profiled the resutls:</p> <ul> <li><p><strong><code>TMultiReadExclusiveWriteSynchronizer</code></strong>: 10,698 ns per iteration<br> 10,697,772,613 ns to iterate 1,000,000 times </p></li> <li><p><strong><code>SRWLock</code></strong>: 8,802 ns per iteration<br> 8,801,678,339 ns to iterate 1,000,000 times</p></li> <li><p><strong><code>Omni Reader-Writer lock</code></strong>: 8,941 ns per iteration<br> 8,940,552,487 ns to iterate 1,000,000 times</p></li> </ul> <p>A 17% improvement when using SRWLocks (aka Omni's spinning lock).</p> <p>Now, i cannot switch the code permanantly over to use <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa904937.aspx" rel="nofollow noreferrer">Windows Vista SRWLocks</a>, as there are some entire enterprises of customers that are still on Windows XP.</p> <p>The Slim locks are just careful use of <code>InterlockedCompareExchange</code> functions; but more careful than i can successfully use. I'm <em>this</em> far away from just stealing the 140 machine instructions involved, and have it done.</p> <h2>Bonus Reading</h2> <ul> <li><a href="https://stackoverflow.com/questions/853316/is-critical-section-always-faster">Is Critical Section always faster?</a></li> <li><a href="http://synopse.info/forum/viewtopic.php?id=322" rel="nofollow noreferrer">How to write fast multi-thread Delphi applications</a></li> </ul>
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    1. CO@DavidHeffernan Oh i had no intention of writing something like that myself. Based on the RTL source code containing `$IFDEF` debugging lines, it would be impossible to write myself. That's why i'm looking for a 3rd party implementation. i don't mind non-native Delphi code - as long as it can be compiled into the native single Win32 executable.
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    2. COWhy are you surprised that so few business customers have not yet upgraded to Windows 7? i have some customers that are hoping that they will soon move SQL Server databases off Windows 2000 Server.
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    3. COHaving to ship `gdiplus.dll` with the application in case they run it on Windows 2000 is still a *joy*.
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