Re: svn commit: r16244 - in trunk: . subversion/clients/cmdline subversion/include subversion/libsvn_client subversion/libsvn_wc subversion/svnversion subversion/tests/clients/cmdline subversion/tests/clients/cmdline/svntest tools/examples

Branko Èibej <brane@xbc.nu> writes:

> Ah-ha. Yes, we have to use CAS because void* may not be atomic. But,
> what's more, we have to use CAS _everywhere_, not just in
> svn_wc_set_adm_dir. Using a NULL comparator and exchange value will
> effectively change the CAS to an atomic read. That won't avoid the
> race, but it will address your other concerns. (No, I'm not prepared
> to assume that void* is atomic, _especially_ not on MP machines.)

That sounds OK. The race is not a problem if there is some other
reason for using CAS; it does look odd if the only reason for using
CAS is to detect a race that is only present because CAS is being
used.

I think the use of CAS should be hidden from Subversion clients as far
as possible. Since svn_wc_set_adm_dir doesn't care about the original
value, and neither will a new svn_wc_get_adm_dir, I think the
Subversion functions should loop until the CAS succeeds so that
clients never need to handle APR_EAGAIN.

-- 
Philip Martin
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