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MARK CALLAGHAN
Did this ever get resolved? I enjoyed reading this, you did a nice job explaining the problem.
It was resolved for x86 in the sense that the code was reverted to the old behaviour. The code is semantically incorrect (uses the wrong barriers), but it happens to generate the correct assembler code on x86 due to its rather strong memory ordering. It is probably still incorrect for some other architectures (eg. multi-core ARM).
Linux had some fun in this area recently -- https://groups.google.com/forum/#!topic/mechanical-sympathy/QbmpZxp6C64
Right. This is very complex technology, very few developers have a full understanding of these issues. And the ones that do can still easily make mistakes.
The InnoDB thread that checked waiting threads once per second for wakeup was a hack to fix a misunderstood bug. Fortunately the amazing Yasufumi
Right. The InnoDB mutex implementation could benefit a lot from being rewritten, I think (and you have written about this as well). I think I heard it mention that MySQL@Oracle are actually working on this (but I do not know details). I am glad you enjoyed reading my write-up. - Kristian.