[Webkit-unassigned] [Bug 108892] Passing alpha to DeferredImageDecoder once decoding completes

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=108892





--- Comment #17 from Min Qin <qinmin at chromium.org>  2013-02-13 20:15:47 PST ---
(In reply to comment #16)
> (From update of attachment 188163 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=188163&action=review
> 
> >> Source/WebCore/platform/graphics/chromium/ImageFrameGenerator.cpp:227
> >> +    return m_hasAlpha;
> > 
> > I know I'll regret asking this, since threading has a long history of making me look like an idiot, but why do you need to lock the mutex for a read?  It's a bool, so all reads should be atomic anyway, no?
> 
> reading a bool should be atomic, but I am not sure whether this is the case with multi-core processor cache.
> If read/write are on different processors, this probably might not hold.

In addition to processor cache, there could be other factors that cause out-of-order execution: pipelining, cache, optimization etc. In such cases, when we set the boolean to false, the code before the set statement might not have been executed yet.

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