<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Wed, Dec 17, 2014 at 2:11 PM, Alexander Richardson <span dir="ltr"><<a href="mailto:arichardson.kde@gmail.com" target="_blank">arichardson.kde@gmail.com</a>></span> wrote:<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">



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      This is an automatically generated e-mail. To reply, visit:
      <a href="https://git.reviewboard.kde.org/r/121570/" target="_blank">https://git.reviewboard.kde.org/r/121570/</a>
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   <h1 style="margin:0;padding:0;font-size:10pt">This change has been marked as submitted.</h1>
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<div>Review request for KDevelop.</div>
<div>By Alexander Richardson.</div>


</span><p style="color:grey"><i>Updated Dec. 17, 2014, 1:11 p.m.</i></p>









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 <b style="color:#575012;font-size:10pt">Repository: </b>
kdevplatform
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<h1 style="color:#575012;font-size:10pt;margin-top:1.5em">Description </h1><div><div class="h5">
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   <pre style="margin:0;padding:0;white-space:pre-wrap;white-space:-moz-pre-wrap;white-space:-pre-wrap;white-space:-o-pre-wrap;word-wrap:break-word"><p style="padding:0;margin:0;line-height:inherit;white-space:inherit">Kill util/spinlock.h, it is actually worse than QMutex in every case</p>
<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">QMutex has changed a lot since this code was introduced and now has the
same kind of logic as SpinLock internally, but implements it a lot more
efficiently. Instead of requiring a QMutex::lock() call and a call to
QWaitCondition::wait() (which is two more compare-and-swap instructions)
it directly uses the futex() syscall.</p>
<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">There are also a few problems with the spinlock code:</p>
<ul style="padding:0;margin:0 0 0 1em;line-height:inherit;white-space:normal">
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<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">It spins using testAndSetOrdered() instead of testAndSetRelaxed().</p>
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<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">There is also no need to unlock using sequentially consistent order,
storeRelease() is enough.</p>
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<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">Even worse is the fact that it uses compare-and-swap
(QAtomicInt::testAndSet<em style="padding:0;margin:0;line-height:inherit;white-space:normal">()) for the spinlock, instead of test-and-set
(QAtomicIn::fetchAndStore</em>()) which would be a lot faster.</p>
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<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">For handling locking with timeout Spinlock uses gettimeofday() which is
not availableon e.g. Windows.</p>
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<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">Finally, the class is poorly named, it isn't a spinlock since it
sleeps in every loop iteration instead of continuously attempting to
acquire the lock.</p>
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<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">A class that actually tries spinning on the lock for a few iterations
before taking the slow path that sleeps MIGHT improve the throughput.
However, finding the right count is hard and will decrease performance
if not chosen correctly.</p>
<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">The easiest way to gain a bit of performance in the locking code would
be to use QBasicMutex for all non-recursive QMutexes, since that would
allow inlining of the fast path lock() code. But since the class is not
documented as public we should probably not do that.</p>
<p style="padding:0;margin:0;line-height:inherit;white-space:inherit">REVIEW: 121570</p></pre>
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<h1 style="color:#575012;font-size:10pt;margin-top:1.5em">Testing </h1>
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   <pre style="margin:0;padding:0;white-space:pre-wrap;white-space:-moz-pre-wrap;white-space:-pre-wrap;white-space:-o-pre-wrap;word-wrap:break-word"><p style="padding:0;margin:0;line-height:inherit;white-space:inherit">Builds</p></pre>
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<h1 style="color:#575012;font-size:10pt;margin-top:1.5em">Diffs </h1>
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 <li>language/backgroundparser/urlparselock.cpp <span style="color:grey">(d113b66b3802818805f87c5b68b0b6f0c933f1f0)</span></li>

 <li>language/duchain/duchain.h <span style="color:grey">(9180cf13e9970b7dd3347ef757b741adab01b733)</span></li>

 <li>util/spinlock.cpp <span style="color:grey">(9b4deeee16ba15e1a9515189a441bc9bd4c1e30f)</span></li>

 <li>util/spinlock.h <span style="color:grey">(cbdb904e39679f136348cb5d6aa8af064c811baf)</span></li>

 <li>serialization/referencecounting.h <span style="color:grey">(3aa0244377f5cbcb128575585beefa98d7f41626)</span></li>

 <li>serialization/referencecounting.cpp <span style="color:grey">(6091c4003fea3573cef779b08b1d4d187c779a7d)</span></li>

 <li>util/CMakeLists.txt <span style="color:grey">(a2287bd2ae10d5e7fa64820e46aa514fa6d18cfe)</span></li>

 <li>language/duchain/duchain.cpp <span style="color:grey">(7ed779d37bcc7075011a901ab09c24522fb651d4)</span></li>

</ul>

<p><a href="https://git.reviewboard.kde.org/r/121570/diff/" style="margin-left:3em" target="_blank">View Diff</a></p>






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</tbody></table></div></div></blockquote><div><br></div><div>FWIW, I'm having huge UI freezes since I last upgraded. Have you tried using it for a while?</div><div><br></div><div>Aleix¬†</div></div></div></div>