From @andk

git bisect

commit 34dadc6
Author​: David Mitchell <davem@​iabyn.com>
Date​: Mon Jul 7 23​:17​:13 2014 +0100

  faster constant hash key lookups ($hash{const})

Note​: the bisect was limited to threaded perls. Text-Xslate-3.3.3
continues to wok on unthreaded perls.

sample fail

http​://www.cpantesters.org/cpan/report/44711096

perl -V

Summary of my perl5 (revision 5 version 21 subversion 2) configuration​:
  Commit id​: 0e22af7
  Platform​:
  osname=linux, osvers=3.14-2-amd64, archname=x86_64-linux-thread-multi
  uname='linux k83 3.14-2-amd64 #1 smp debian 3.14.13-2 (2014-07-24) x86_64 gnulinux '
  config_args='-Dprefix=/home/sand/src/perl/repoperls/installed-perls/perl/v5.21.2/9980 -Dmyhostname=k83 -Dinstallusrbinperl=n -Uversiononly -Dusedevel -des -Ui_db -Duseithreads -Uuselongdouble -DDEBUGGING=-g'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=define, usemultiplicity=define
  use64bitint=define, use64bitall=define, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2',
  optimize='-O2 -g',
  cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
  ccversion='', gccversion='4.9.1', gccosandvers=''
  intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
  libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.9/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
  libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc -lgdbm_compat
  perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
  libc=libc-2.19.so, so=so, useshrplib=false, libperl=libperl.a
  gnulibc_version='2.19'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
  cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib -fstack-protector'

Characteristics of this binary (from libperl)​:
  Compile-time options​: HAS_TIMES MULTIPLICITY PERLIO_LAYERS
  PERL_DONT_CREATE_GVSV
  PERL_HASH_FUNC_ONE_AT_A_TIME_HARD
  PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP
  PERL_NEW_COPY_ON_WRITE PERL_PRESERVE_IVUV
  PERL_USE_DEVEL USE_64_BIT_ALL USE_64_BIT_INT
  USE_ITHREADS USE_LARGE_FILES USE_LOCALE
  USE_LOCALE_COLLATE USE_LOCALE_CTYPE
  USE_LOCALE_NUMERIC USE_LOCALE_TIME USE_PERLIO
  USE_PERL_ATOF USE_REENTRANT_API
  Built under linux
  Compiled at Aug 1 2014 04​:36​:41
  %ENV​:
  PERL5LIB=""
  PERL5OPT=""
  PERL5_CPANPLUS_IS_RUNNING="7063"
  PERL5_CPAN_IS_RUNNING="7063"
  PERL_MM_USE_DEFAULT="1"
  @​INC​:
  /home/sand/src/perl/repoperls/installed-perls/perl/v5.21.2/9980/lib/site_perl/5.21.2/x86_64-linux-thread-multi
  /home/sand/src/perl/repoperls/installed-perls/perl/v5.21.2/9980/lib/site_perl/5.21.2
  /home/sand/src/perl/repoperls/installed-perls/perl/v5.21.2/9980/lib/5.21.2/x86_64-linux-thread-multi
  /home/sand/src/perl/repoperls/installed-perls/perl/v5.21.2/9980/lib/5.21.2
  .
--
andreas

From @cpansprout

On Sun Aug 31 05​:19​:31 2014, andreas.koenig.7os6VVqR@​franz.ak.mind.de wrote​:

git bisect
----------
commit 34dadc6
Author​: David Mitchell <davem@​iabyn.com>
Date​: Mon Jul 7 23​:17​:13 2014 +0100

faster constant hash key lookups ($hash{const})

Note​: the bisect was limited to threaded perls. Text-Xslate-3.3.3
continues to wok on unthreaded perls.

sample fail
-----------
http​://www.cpantesters.org/cpan/report/44711096

I haven’t looked into the failure yet, but parts of that commit don’t make sense to me​:

  /* keysv is actually a HEK in disguise, so we can match just by
  * comparing the HEK pointers in the HE chain. There is a slight
  * caveat​: on something like "\x80", which has both plain and utf8
  * representations, perl's hashes do encoding-insensitive lookups,
  * but preserve the encoding of the stored key. Thus a particular
  * key could map to two different HEKs in PL_strtab. We only
  * conclude 'not found' if all the flags are the same; otherwise
  * we fall back to a full search (this should only happen in rare
  * cases).
  */
  int keysv_flags = HEK_FLAGS(keysv_hek);
  HE *orig_entry = entry;

  for (; entry; entry = HeNEXT(entry)) {
  HEK *hek = HeKEY_hek(entry);
  if (hek == keysv_hek)
  goto found;
  if (HEK_FLAGS(hek) != keysv_flags)
  break; /* need to do full match */
  }

Since the flags are stored as part of the hek, shouldn’t a simple address equality check be sufficient?

What that code is doing is falling back to the old code if a hash contains *any* entries (prior to the one we want) that have flags differing from the sought entry.

--

Father Chrysostomos

The RT System itself - Status changed from 'new' to 'open'

From @cpansprout

On Sun Aug 31 07​:05​:35 2014, sprout wrote​:

On Sun Aug 31 05​:19​:31 2014, andreas.koenig.7os6VVqR@​franz.ak.mind.de
wrote​:

git bisect
----------
commit 34dadc6
Author​: David Mitchell <davem@​iabyn.com>
Date​: Mon Jul 7 23​:17​:13 2014 +0100

faster constant hash key lookups ($hash{const})

Note​: the bisect was limited to threaded perls. Text-Xslate-3.3.3
continues to wok on unthreaded perls.

sample fail
-----------
http​://www.cpantesters.org/cpan/report/44711096

I haven’t looked into the failure yet, but parts of that commit don’t
make sense to me​:

Never mind that. I wasn’t thinking straight.

--

Father Chrysostomos

From @iabyn

On Sun, Aug 31, 2014 at 05​:19​:32AM -0700, Andreas J. Koenig via RT wrote​:

git bisect
----------
commit 34dadc6
Author​: David Mitchell <davem@​iabyn.com>
Date​: Mon Jul 7 23​:17​:13 2014 +0100

faster constant hash key lookups \($hash\{const\}\)

Note​: the bisect was limited to threaded perls. Text-Xslate-3.3.3
continues to wok on unthreaded perls.

It's a thread-safety issue in Mouse (which Text-Xslate uses), and which
that perl commit just happens to tickle.

I'll raise a ticket against Mouse.

--
Dave's first rule of Opera​:
If something needs saying, say it​: don't warble it.

@iabyn - Status changed from 'open' to 'resolved'