677685 - Implement CompareAndSwapPointers

Status: RESOLVED WONTFIX

(Core :: General, defect)

Comment 1

[Justin Lebar (not reading bugmail)]

Attachment: Patch from bug 670967

dzbarsky, does this do what you want?

Comment 2

[David Zbarsky (:dzbarsky)]

Looks good, but try to avoid code duplications with js_CompareAndSwap.

Comment 3

[Justin Lebar (not reading bugmail)]

I'd originally had this in mfbt, but I took it out because I wanted to be able to use mozilla::Mutex.  But in a newer version of the patch (which I'll attach in a moment), I'm no longer using a static mozilla::Mutex because it leaks, and it's hard to instantiate a mutex without allocating any memory (which is necessary for bug 670967).

bsmedberg, What would you think about moving this code into mfbt?

Comment 4

[Justin Lebar (not reading bugmail)]

(In reply to David Zbarsky from comment #2)
> Looks good, but try to avoid code duplications with js_CompareAndSwap.

Looking at this more closely, I'm not sure it makes much sense to try to de-duplicate here.  It's a small amount of code, and js_CompareAndSwap's interface is different.

We could still move it to mfbt if we wanted...

David, do you have pointers, or jsword's?  If you have jswords, you'll have to do some nasty casting to make things work with this interface -- the whole point was to avoid this.

Comment 5

[David Zbarsky (:dzbarsky)]

Unfortunately they're jswords.  I couldn't get this to work even with the nasty casting.

Comment 6

[Justin Lebar (not reading bugmail)]

This apparently doesn't help David after all.  WONTFIX.

Comment 7

[David Zbarsky (:dzbarsky)]

Justin, I think your MSVC implementations are wrong.  Shouldn't the argument to InterlockedCompareExchange be in the opposite order?  See http://msdn.microsoft.com/en-us/library/ms683560%28v=vs.85%29.aspx

Comment 8

[Justin Lebar (not reading bugmail)]

Oh man, and I even had it right in the 64-bit version!

Thanks for noticing, David!

Comment 9

[Justin Lebar (not reading bugmail)]

Attachment: Part 1, v4: Add atomic pointer operations.

Comment 10

[Justin Lebar (not reading bugmail)]

Attachment: Part 1, v4: Add atomic pointer operations.