Thread: Can a Locking mechanism be implemented stricly with software?

Hardware locking is the only reliable way to guarantee atomicity. It's virtually impossible to implement a locking mechanism in software without guaranteed atomicity. Most modern processors support hardware locking of memory. The intel processors and their clones implement a "lock" prefix for certain instructions, which takes exclusive ownership of a cache line for the data referenced by the instruction that follows the lock prefix.

Originally Posted by Absurd

Hi.
I know it is not Linux related per seh, but I couldn't find any other suitable place for this question that bothers me for quite a lot, and I couldn't find the answer online.

Suppose I want to implement a locking mechanism.
Is there a way to do it without the help of hardware?
For example, the Test-And-Set function, afaik, is implemented using hardware to allow atomicity.
Is atomicity a necessary component for a locking mechanism?
Because if it is, then I can't think of any way to implement it without the help of some designated hardware...

I find the question a little odd... I mean, everything that software does is dependent on hardware support. When you add two integers it only works because there is hardware support.

Suppose there was a way to implement locking "in software" without a dedicated instruction for atomic access to a memory location. How exactly would that operation (however it looked) be independent of the hardware? You seem to be drawing a completely arbitrary line and saying that things on this side of the line are "supported by hardware" and the things on the other side happen... through magic, I guess?