RE: atomic operations in user space

-----Original Message-----
From: Brent Cook [mailto:bcook@bpointsys.com]
Sent: Thursday, August 24, 2006 10:18 PM
To: linuxppc-embedded@ozlabs.org
Cc: Li Yang-r58472; Terry Liang
Subject: Re: atomic operations in user space
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On Thursday 24 August 2006 05:39, Li Yang-r58472 wrote:
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quoted

Why do you need atomic operations in user land? IPC will be

sufficient

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quoted

to deal with race conditions between processes.

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quoted

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quoted

Best Regards,

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quoted

Leo

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What about multiple threads within a process updating a counter?

Is there anything preventing semaphore to be used in threads?

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Of course, if you look at these functions in the kernel header,

they're just 2 or

3 inline assembly calls - you could easily rewrite them. Google for

'PowerPC atomic

increment' and grab one of the unencumbered implementations if you

need to use it

in a non-GPL program.
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On the other hand, I see no license at the top of my

/usr/include/asm-i386/atomic.h

file at all, same for PowerPC - are Linux header files actually GPL or

are they

more like the glibc headers, with exceptions made for userspace

programs?

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The atomic operations on x86 were accidentally exported early on, so

they have to

hang around apparently for compatibility (there are some mailing list

threads out

there to this effect.) Currently, you just have to assume in Linux

that if you

include something from /usr/include/linux or asm that it will not

necessarily be

cross-version or cross-architecture compatible. Not every arch in

Linux even has

atomic operations of this nature, which I guess is the main reason why

they are

not exported in general.
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- Brent