[PATCH][BZ #13065] New pthread_barrier algorithm to fulfill barrier destruction requirements.

[Torvald Riegel]

On Sun, 2015-07-19 at 23:52 +0200, Torvald Riegel wrote:
> The previous barrier implementation did not fulfill the POSIX
> requirements for when a barrier can be destroyed.  Specifically, it was
> possible that threads that haven't noticed yet that their round is
> complete still access the barrier's memory, and that those accesses can
> happen after the barrier has been legally destroyed.
> The new algorithm does not have this issue, and it avoids using a lock
> internally.
> 
> Tested on x86_64-linux.
> 
> Dave, I haven't touched sparc yet, and applying this patch would break
> sparc I think because of the internaltypes.h change.  What do you want
> to do?  One option would be wait for the barrier to get ready for
> master, and then copy for sparc and adapt for sparc32.
> 
> This is not meant for 2.22.

Ping.  Attached is a rebased patch.

It would be nice to have this in 2.23.


2015-12-18  Torvald Riegel  <triegel@redhat.com>

        [BZ #13065]
        * nptl/pthread_barrier_wait.c (__pthread_barrier_wait): Replace with
        new implementation.
        * nptl/pthread_barrier_destroy.c (pthread_barrier_destroy): Likewise.
        * nptl/pthread_barrier_init.c (__pthread_barrier_init): Adapt.
        * sysdeps/nptl/internaltypes.h (pthread_barrier): Adapt.
        (BARRIER_IN_THRESHOLD): New macro.
        * nptl/pthread_barrierattr_setpshared.c
        (pthread_barrierattr_setpshared): Clean up.
        * nptl/tst-barrier4.c: Correct comment.
        * nptl/tst-barrier5.c: New file.
        * nptl/Makefile (tests): Add nptl/tst-barrier5.c.
        (gen-as-const-headers): Remove lowlevelbarrier.sym.
        * sysdeps/unix/sysv/linux/i386/pthread_barrier_wait.S: Remove.
        * sysdeps/unix/sysv/linux/x86_64/pthread_barrier_wait.S: Remove.
        * nptl/lowlevelbarrier.sym: Remove.

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