atomicity in 32/64 bit
the question is about when does a 64b开发者_如何转开发it load/store operations are considered to be atomic.
- if i have a 64bit processor, but i'm using 32bit OS. Will i have 64bit atomicity?
- if i'm using 64bit OS but running an 32bit application (using WoW64), will i have 64bit atomicity?
The application must be running on a 64bit OS and in native 64bit mode to gain the advantages of x64, unsurprisingly. If you're running in 32bit mode, either on a 32bit OS (with a 32bit app), you will get 32bit atomicity. If you're running 64bit mode on a 64bit OS on a 64bit CPU, you will get 64bit atomicity. All of the components in the chain (app, OS, CPU) must be running 64bit to get 64bit.
Not by default! But some SSE instructions under x86 support 64bit and 128bit atomic load/store, of course you must first ensure memory aligment. Look examples:
procedure Move64(var Source, Destination);
//Move 8 bytes atomicly from Source 8-byte aligned to Destination!
asm
movq xmm0, qword [Source]
movq qword [Destination], xmm0
end;
procedure Move64(newData: pointer; newReference: cardinal; var Destination); overload;
//Move 8 bytes atomically into 8-byte Destination!
asm
movd xmm0, eax
movd xmm1, edx
punpckldq xmm0, xmm1
movq qword [Destination], xmm0
end;
procedure Move128(var Source, Destination);
//Move 16 bytes atomicly from Source to 16-byte aligned to Destination!
asm
movdqa xmm0, dqword [Source]
movdqa dqword [Destination], xmm0
end;
It is only the 32/64 "bitness" of the application that matters -
i.e. that your 64 bit loads/stores are atomic at the assembly level.
You need a 64 bit application to get that for "free".*
For the 64 bit application you need a 64 bit CPU and an OS that can execute it.
The OS can be anything, as long as it can start a 64 bit process on a 64 bit CPU.
if i have a 64bit processor, but i'm using 32bit OS. Will i have 64bit atomicity?
32 bit Windows, Linux: You simply cannot run 64 bit applications on 32 bit Windows or Linux, even on a 64 bit CPU.
32 bit Mac OS X: If your application is a 64 bit app, then yes.
if i'm using 64bit OS but running an 32bit application (using WoW64), will i have 64bit atomicity?
No. Your loads and stores at the machine code level will still be 32 bit loads and stores if you are running a 32 bit application.
*You can get 64 bit atomic reads/writes on a 32 bit CPU with compiler intrinsics where available and/or direct assembly.
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