libthr shared locks

Konstantin Belousov kostikbel at
Thu Dec 24 19:14:15 UTC 2015

On Thu, Dec 24, 2015 at 01:46:25PM -0500, Daniel Eischen wrote:
> Can we still implement things like robust and priority mutexes in a
> pshared mutex with Konstantin's implementation?  The rest of the world
> (Linux, Solaris anyway) use structs and get by just fine ABI-wise.
Yes, we do. I intend to do this as the next stage, planned the
implementation and did some preparations for it in the current patch.
This raises the question, why do you suppose that my approach with
the off-page would not allow it ? I am asking not to argument, but to
understand a possible shortcoming in the approach, which I missed.

>From the implementation PoV, off-page is completely equivalent to the
in-line structs approach, and the difference is only in the initial
translation of say pthread_mutex_t to the structure (off-page lookup vs.
identity). The issues with maintaining the lists of the owned robust of
pi mutexes are same, and in fact you could see some non-trivial traces
of this in the _mutex_fork() reimplementation in my patch.

Linux and Solaris get (large enough) structs early enough to avoid the ABI
issues.  I remember Linux changing FILE layout in early days of glibc 2.0
and resulting pain, while they already had the GNU symbol versioning
working and used.

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