[Development] QBasicMutex::lockInternal() race condition?

[Thiago Macieira]

On sexta-feira, 21 de setembro de 2012 13.42.13, Tony Van Eerd wrote:
> By the way, I assume the intent is to limit the implementation to only using
> int/pointer-sized atomics, not double width atomics?

We can use double-width atomics if necessary. But the only architecture for 
which I implemented that is x86 32-bit (via cmpxchg8b). And even then, the 
assembly is very fragile, since it requires no less than 5 registers and a 
memory operand. Very often, gcc bails out by not being able to allocate 
registers.

Double-width atomics must be a solution to other problems, not a requirement, 
since they don't exist on all platforms. For LL/SC platforms, we need a 
different implementation. For Itanium, we must figure out a way of working with 
the weird "compare 8 exchange 16" instruction. Finally, for x86-64, we need a 
fallback because early 64-bit processors were missing the CMPXCHG16B 
instruction.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
     Intel Sweden AB - Registration Number: 556189-6027
     Knarrarnäsgatan 15, 164 40 Kista, Stockholm, Sweden
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