[Bug nptl/15215] New: Unify pthread_once implementations.

[Bug nptl/15215] New: Unify pthread_once implementations.

[carlos at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15215

             Bug #: 15215
           Summary: Unify pthread_once implementations.
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: nptl
        AssignedTo: unassigned@sourceware.org
        ReportedBy: carlos@redhat.com
                CC: drepper.fsp@gmail.com
    Classification: Unclassified


At present we have several different algorithms for implementing the core of
pthread_once.

The following machines share one implementation, call this I1:

ports/sysdeps/unix/sysv/linux/hppa/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/ia64/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c
nptl/sysdeps/unix/sysv/linux/sparc/pthread_once.c

The following machines share another implementation, call this I2:

ports/sysdeps/unix/sysv/linux/m68k/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/arm/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/aarch64/nptl/pthread_once.c

The following machines have custom implementations:

nptl/sysdeps/unix/sysv/linux/sh/pthread_once.S
nptl/sysdeps/unix/sysv/linux/i386/pthread_once.S
nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S
nptl/sysdeps/unix/sysv/linux/powerpc/pthread_once.c
nptl/sysdeps/unix/sysv/linux/s390/pthread_once.c
ports/sysdeps/unix/sysv/linux/alpha/nptl/pthread_once.c

(a) Verify I1 is functionally equivalent to I2.
- Someone should verify that the algorithm used in I1 is equivalent to I2.
- If I1 is not equivalent to I2 then the algorithm should be fixed one way or
the other to produce a functioning single implementation called IC. Do not
cleanup any of the magic numbers yet since that's (c).
- Post analysis and patch (if you changed a representative implementation) to
libc-alpha@sourceware.org and libc-ports@sourceware.org and suggest (b).

Notes:
- It would appear that in I2 the setting of once_control via:
"*once_control = __fork_generation | 2;" may not have the release semantics
required by the earlier "atomic_compare_and_exchange_val_acq (once_control,
newval, oldval)". This means I2 is not actually safe for systems that have
weakly ordered memory writes.

(b) Use IC for all machines that do not have custom implementations.
- Place IC in nptl/sysdeps/unix/sysv/linux/pthread_once.c
- Remove:
ports/sysdeps/unix/sysv/linux/hppa/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/ia64/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c
nptl/sysdeps/unix/sysv/linux/sparc/pthread_once.c
ports/sysdeps/unix/sysv/linux/m68k/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/arm/nptl/pthread_once.c
ports/sysdeps/unix/sysv/linux/aarch64/nptl/pthread_once.c
The builds will fall back to using the newly installed IC.
- Post patch to libc-alpha@sourceware.org and libc-ports@sourceware.org, garner
consensus, and checkin changes.

(c) Cleanup IC.
- We magically add +4 in nptl/sysdeps/unix/sysv/linux/fork.c to the fork
generation counter, that's simply to avoid the low-two bits which we use in
control object to indicate done running init_routine (bit 2 set) or running
init_routine (bit 1 set). We should use a macro here like
__PTHREAD_ONCE_FORK_GEN and define it in nptl/pthreadP.h.
- Similarly the IC should use:
/* Used by pthread_once and fork coordination.  */
#define __PTHREAD_ONCE_RUN      1       /* Running the initializer.  */
#define __PTHREAD_ONCE_DONE     2       /* Initializer done running.  */
#define __PTHREAD_ONCE_MASK     3       /* Status bit mask.  */
instead of the magic & 2, or | 1, etc, that appear in the implementation.
- Get rid of the `& -4' magic, we all know this is actually
`~(__PTHREAD_ONCE_FORK_GEN - 1)' which makes a lot more sense to most people
and generates the same code.
- Make sure that the atomic update to the control object has the correct
semantics e.g. release.

(d) Review i386 and x86_64 implementations.
- Review:
nptl/sysdeps/unix/sysv/linux/i386/pthread_once.S
nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S
- How do those compare to IC?
- Try compiling IC for i386 and x86_64 by simply removing the assembly
implementation and examine the generated assembly to see if it's any better or
the same as the custom assembly versions.
- Post any interesting findings to libc-alpha@sourceware.org.

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[Bug nptl/15215] Unify pthread_once implementations.

[carlos at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15215

Carlos O'Donell <carlos at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |triegel at redhat dot com

--- Comment #1 from Carlos O'Donell <carlos at redhat dot com> ---
Torvald is looking at this.

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[Bug nptl/15215] Unify pthread_once implementations.

[carlos at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15215

Carlos O'Donell <carlos at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

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[Bug nptl/15215] Unify pthread_once implementations.

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15215

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  36875b06e0ed7f137190b9228bef553adfc338ba (commit)
      from  579db35a068e70a4f3112000778138ede6994ac0 (commit)

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=36875b06e0ed7f137190b9228bef553adfc338ba

commit 36875b06e0ed7f137190b9228bef553adfc338ba
Author: Torvald Riegel <triegel@redhat.com>
Date:   Wed May 8 16:35:10 2013 +0200

    Fixed and unified pthread_once.

    [BZ #15215] This unifies various pthread_once architecture-specific
    implementations which were using the same algorithm with slightly different
    implementations.  It also adds missing memory barriers that are required
for
    correctness.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                          |   13 ++
 nptl/sysdeps/unix/sysv/linux/pthread_once.c        |  131 ++++++++++++++++++++
 nptl/sysdeps/unix/sysv/linux/sparc/pthread_once.c  |   93 --------------
 ports/ChangeLog.hppa                               |    5 +
 .../unix/sysv/linux/hppa/nptl/pthread_once.c       |   93 --------------
 .../unix/sysv/linux/aarch64/nptl/pthread_once.c    |   90 --------------
 sysdeps/unix/sysv/linux/arm/nptl/pthread_once.c    |   89 -------------
 sysdeps/unix/sysv/linux/ia64/nptl/pthread_once.c   |   93 --------------
 sysdeps/unix/sysv/linux/m68k/nptl/pthread_once.c   |   90 --------------
 sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c   |   93 --------------
 sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c   |   94 --------------
 11 files changed, 149 insertions(+), 735 deletions(-)
 create mode 100644 nptl/sysdeps/unix/sysv/linux/pthread_once.c
 delete mode 100644 nptl/sysdeps/unix/sysv/linux/sparc/pthread_once.c
 delete mode 100644 ports/sysdeps/unix/sysv/linux/hppa/nptl/pthread_once.c
 delete mode 100644 sysdeps/unix/sysv/linux/aarch64/nptl/pthread_once.c
 delete mode 100644 sysdeps/unix/sysv/linux/arm/nptl/pthread_once.c
 delete mode 100644 sysdeps/unix/sysv/linux/ia64/nptl/pthread_once.c
 delete mode 100644 sysdeps/unix/sysv/linux/m68k/nptl/pthread_once.c
 delete mode 100644 sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c
 delete mode 100644 sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c

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[Bug nptl/15215] Unify pthread_once implementations.

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15215

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com
              Flags|                            |security-

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[Bug nptl/15215] Unify pthread_once implementations.

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15215

--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  63668b7084ac26865136e59fdf17781f9f49bd99 (commit)
      from  42b7f5d48549b85386a9b28a1a90e66fd81ba273 (commit)

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=63668b7084ac26865136e59fdf17781f9f49bd99

commit 63668b7084ac26865136e59fdf17781f9f49bd99
Author: Torvald Riegel <triegel@redhat.com>
Date:   Fri Oct 11 18:58:04 2013 +0300

    pthread_once: Clean up constants.

    [BZ #15215] This just gives a name to the integer constants being used.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog           |    9 +++++++++
 nptl/pthreadP.h     |    6 ++++++
 nptl/pthread_once.c |   21 ++++++++++++---------
 sysdeps/nptl/fork.c |    3 ++-
 4 files changed, 29 insertions(+), 10 deletions(-)

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[Bug nptl/15215] Unify pthread_once implementations.

[triegel at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15215

Torvald Riegel <triegel at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Torvald Riegel <triegel at redhat dot com> ---
Fixed with f50277c19df0937ea9691ab7e7c642ecd3ed3d94.

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[Bug nptl/15215] Unify pthread_once implementations.

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15215

--- Comment #5 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
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The branch, master has been updated
       via  b09adb5b46327e4a2ea354d5524280146d9c6015 (commit)
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commit b09adb5b46327e4a2ea354d5524280146d9c6015
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri Oct 31 21:21:15 2014 +0000

    Add bug 15215 to NEWS; move bug 17344 to correct version's list in NEWS.

-----------------------------------------------------------------------

Summary of changes:
 NEWS |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

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