Does Interlocked.CompareExchange(double,double,double) work in 32 bit OS?
I'm maintaining a high performance class that can be operated on by multiple threads. Many of 开发者_如何学Pythonthe fields are volatile ints, and as it turns out I need to upgrade one of those to a double. I'm curious if there is a lock free way to do this, and was wondering if the Interlocked.CompareExchange(double, double, double)
works as advertised on a 32-bit OS, or are torn reads a problem.
This page details the intrinsics of the "native" Interlocked functions. It mentions the following limitations
Because _InterlockedCompareExchange64 uses the cmpxchg8b instruction, it is not available on pre-Pentium processors, such as the 486.
So we can expect that it is available and also implemented as an interlocked instruction operation (rather than being simulated by using a full lock).
Yes, it works as described on 32-bit. That's what the Interlocked
methods are there for.
Yes, it's works.
It uses InterlockedCompareExchange64 - if you want to have a look at a possible implementation in x86 asm, have a look here - http://qc.embarcadero.com/wc/qcmain.aspx?d=6212.
asm
// -> EAX Destination
// ESP+4 Exchange
// ESP+12 Comperand
// <- EDX:EAX Result
PUSH EBX
PUSH EDI
MOV EDI, EAX
MOV EAX, DWORD PTR [Comperand]
MOV EDX, DWORD PTR [Comperand+4]
MOV EBX, DWORD PTR [Exchange]
MOV ECX, DWORD PTR [Exchange+4]
LOCK CMPXCHG8B [EDI]
POP EDI
POP EBX
end;
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