From @jdv

[jdv@​wieldy ~]$ cat test_grammar_1_thread.p6
use v6;

use XML;

PROCESS​::<$SCHEDULER>
  = ThreadPoolScheduler.new(initial_threads => 0, max_threads => 1);

await map { start {
  my $xml = from-xml(
  '<upper id="one"><lower class="odd" id="one.1" /></upper>'
  );
} }, ^100;
[jdv@​wieldy ~]$ perl6 test_grammar_1_thread.p6
[jdv@​wieldy ~]$ perl6 test_grammar_1_thread.p6
[jdv@​wieldy ~]$ perl6 test_grammar_1_thread.p6
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ cat test_grammar_no_async.p6
use v6;

use XML;

map {
  my $xml = from-xml(
  '<upper id="one"><lower class="odd" id="one.1" /></upper>'
  );
}, ^100;
[jdv@​wieldy ~]$ perl6 test_grammar_no_async.p6
[jdv@​wieldy ~]$ perl6 test_grammar_no_async.p6
[jdv@​wieldy ~]$ perl6 test_grammar_no_async.p6
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ cat test_grammar_n_threads.p6
use v6;

use XML;

await map { start {
  my $xml = from-xml(
  '<upper id="one"><lower class="odd" id="one.1" /></upper>'
  );
} }, ^100;
[jdv@​wieldy ~]$ perl6 test_grammar_n_threads.p6
Use of uninitialized value $!made of type Any in string context
Any of .^name, .perl, .gist, or .say can stringify undefined things, if
needed.Use of uninitialized value $!made of type Any in string context
Any of .^name, .perl, .gist, or .say can stringify undefined things, if
needed. in block at
/home/jdv/rakudo/install/share/perl6/site/sources/9C152F2320E9F47891023366BF40420AE8E7F235
(XML​::Element) line 327
Use of uninitialized value $!made of type Any in string context
Any of .^name, .perl, .gist, or .say can stringify undefined things, if
needed. in block at
/home/jdv/rakudo/install/share/perl6/site/sources/9C152F2320E9F47891023366BF40420AE8E7F235
(XML​::Element) line 327
  in block at
/home/jdv/rakudo/install/share/perl6/site/sources/9C152F2320E9F47891023366BF40420AE8E7F235
(XML​::Element) line 327
[jdv@​wieldy ~]$ perl6 test_grammar_n_threads.p6
*** Error in `/home/jdv/rakudo/install/bin/moar'​: double free or
corruption (fasttop)​: 0x000000000533c8a0 ***
======= Backtrace​: =========
/lib64/libc.so.6(+0x77d9e)[0x7f6585d5fd9e]
/lib64/libc.so.6(cfree+0x5b5)[0x7f6585d6b9f5]
//home/jdv/rakudo/install/lib/libmoar.so(MVM_interp_run+0x13b83)[0x7f658620d813]
//home/jdv/rakudo/install/lib/libmoar.so(+0x1774be)[0x7f658621c4be]
//home/jdv/rakudo/install/lib/libmoar.so(+0x23cf17)[0x7f65862e1f17]
/lib64/libpthread.so.0(+0x752a)[0x7f65857cb52a]
/lib64/libc.so.6(clone+0x6d)[0x7f6585de822d]
======= Memory map​: ========
00400000-00402000 r-xp 00000000 fd​:00 1704740
/home/jdv/rakudo/install/bin/moar
00601000-00602000 r--p 00001000 fd​:00 1704740
/home/jdv/rakudo/install/bin/moar
00602000-00603000 rw-p 00002000 fd​:00 1704740
/home/jdv/rakudo/install/bin/moar
00f1e000-05580000 rw-p 00000000 00​:00 0
[heap]
7f6560000000-7f6560021000 rw-p 00000000 00​:00 0
7f6560021000-7f6564000000 ---p 00000000 00​:00 0
7f6564000000-7f6564021000 rw-p 00000000 00​:00 0
7f6564021000-7f6568000000 ---p 00000000 00​:00 0
7f6568000000-7f6568021000 rw-p 00000000 00​:00 0
7f6568021000-7f656c000000 ---p 00000000 00​:00 0
7f656c000000-7f656c021000 rw-p 00000000 00​:00 0
7f656c021000-7f6570000000 ---p 00000000 00​:00 0
7f65711e2000-7f65711e3000 ---p 00000000 00​:00 0
7f65711e3000-7f65719e3000 rwxp 00000000 00​:00 0
7f65719e3000-7f6571de4000 rw-p 00000000 00​:00 0
7f6571de4000-7f6571de5000 ---p 00000000 00​:00 0
7f6571de5000-7f65725e5000 rwxp 00000000 00​:00 0
[stack​:21428]
7f65725e5000-7f65725fb000 r-xp 00000000 fd​:00 1976029
/usr/lib64/libgcc_s-4.9.2-20150212.so.1
7f65725fb000-7f65727fa000 ---p 00016000 fd​:00 1976029
/usr/lib64/libgcc_s-4.9.2-20150212.so.1
7f65727fa000-7f65727fb000 r--p 00015000 fd​:00 1976029
/usr/lib64/libgcc_s-4.9.2-20150212.so.1
7f65727fb000-7f65727fc000 rw-p 00016000 fd​:00 1976029
/usr/lib64/libgcc_s-4.9.2-20150212.so.1
7f65727fc000-7f6572bfd000 rw-p 00000000 00​:00 0
7f6572bfd000-7f6572bfe000 ---p 00000000 00​:00 0
7f6572bfe000-7f65733fe000 rwxp 00000000 00​:00 0
[stack​:21427]
7f65733fe000-7f65737ff000 rw-p 00000000 00​:00 0
7f65737ff000-7f6573800000 ---p 00000000 00​:00 0
7f6573800000-7f6574000000 rwxp 00000000 00​:00 0
[stack​:21426]
7f6574000000-7f6574053000 rw-p 00000000 00​:00 0
7f6574053000-7f6578000000 ---p 00000000 00​:00 0
7f6578000000-7f6578039000 rw-p 00000000 00​:00 0
7f6578039000-7f657c000000 ---p 00000000 00​:00 0
7f657c000000-7f657c08c000 rw-p 00000000 00​:00 0
7f657c08c000-7f6580000000 ---p 00000000 00​:00 0
7f658006b000-7f658006c000 rw-p 00000000 00​:00 0
7f658006c000-7f6580073000 r-xp 00000000 00​:00 0
7f6580073000-7f6580475000 rw-p 00000000 00​:00 0
7f6580475000-7f6580476000 ---p 00000000 00​:00 0
7f6580476000-7f6580c76000 rwxp 00000000 00​:00 0
[stack​:21425]
7f6580c76000-7f6581077000 rw-p 00000000 00​:00 0
7f6581077000-7f6581078000 ---p 00000000 00​:00 0
7f6581078000-7f6581878000 rwxp 00000000 00​:00 0
[stack​:21424]
7f6581878000-7f6581c79000 rw-p 00000000 00​:00 0
7f6581c79000-7f6581c7a000 ---p 00000000 00​:00 0
7f6581c7a000-7f658247a000 rwxp 00000000 00​:00 0
[stack​:21423]
7f658247a000-7f658287b000 rw-p 00000000 00​:00 0
7f658287b000-7f658287c000 ---p 00000000 00​:00 0
7f658287c000-7f658307c000 rwxp 00000000 00​:00 0
[stack​:21422]
7f658307c000-7f658347d000 rw-p 00000000 00​:00 0
7f658347d000-7f6583499000 r-xp 00000000 00​:00 0
7f6583499000-7f65834a6000 r--p 00000000 fd​:00 1705876
/home/jdv/.perl6/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/A2/A2B4F888E6596500108BE775C24FB2FB530C959F
7f65834a6000-7f65834a9000 r-xp 00000000 00​:00 0
7f65834a9000-7f65834b7000 r--p 00000000 fd​:00 1705877
/home/jdv/.perl6/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/78/78DE25E088102CDEC6D4A57D261A577D9355F241
7f65834b7000-7f65834db000 r--p 00000000 fd​:00 1705874
/home/jdv/.perl6/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/9C/9C152F2320E9F47891023366BF40420AE8E7F235
7f65834db000-7f65834f1000 r--p 00000000 fd​:00 1705804
/home/jdv/rakudo/install/share/perl6/site/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/0F/0F062602D8D953D4B71A91EF3D0954E39738CA2E
7f65834f1000-7f65834f5000 r--p 00000000 fd​:00 1705805
/home/jdv/rakudo/install/share/perl6/site/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/0F/0F7FE949FBE23C216C1BCE87A38F2BA268F2DEDE
7f65834f5000-7f65834f9000 r--p 00000000 fd​:00 1705802
/home/jdv/rakudo/install/share/perl6/site/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/8B/8BEC55BA74542DFB645FD30E5A36E0F292307490
7f65834f9000-7f6583502000 r--p 00000000 fd​:00 1705791
/home/jdv/rakudo/install/share/perl6/site/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/A9/A9AC5A8C89A20770906AD0AEE2023BBAE0919F3B
7f6583502000-7f6583503000 r-xp 00000000 00​:00 0
7f6583503000-7f658350a000 r--p 00000000 fd​:00 1705799
/home/jdv/rakudo/install/share/perl6/site/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/87/873970C06476994E8C2AAF771405BEA0B914F92E
7f658350a000-7f658350f000 r--p 00000000 fd​:00 1705792
/home/jdv/rakudo/install/share/perl6/site/precomp/4C98C700658D7065E222FD0683D39ADB6B60718C.1470245592.49939/5A/5A18C88954104D1A210C4B3ED26F27E47F264AA7
7f658350f000-7f6583740000 r-xp 00000000 00​:00 0
7f6583740000-7f6583b41000 rw-p 00000000 00​:00 0
7f6583b41000-7f6583b66000 r-xp 00000000 00​:00 0
7f6583b66000-7f6583cc7000 rw-p 00000000 00​:00 0
7f6583cc7000-7f6583d0e000 r--p 00000000 fd​:00 1705208
/home/jdv/rakudo/install/share/nqp/lib/Perl6/Metamodel.moarvm
7f6583d0e000-7f6583d3a000 r--p 00000000 fd​:00 1705209
/home/jdv/rakudo/install/share/nqp/lib/Perl6/BOOTSTRAP.moarvm
7f6583d3a000-7f6583d66000 rw-p 00000000 00​:00 0
7f6583d66000-7f65847f3000 r--p 00000000 fd​:00 1705214
/home/jdv/rakudo/install/share/perl6/runtime/CORE.setting.moarvm
7f65847f3000-7f65847f9000 r-xp 00000000 fd​:00 1705219
/home/jdv/rakudo/install/share/perl6/runtime/dynext/libperl6_ops_moar.so
7f65847f9000-7f65849f8000 ---p 00006000 fd​:00 1705219
/home/jdv/rakudo/install/share/perl6/runtime/dynext/libperl6_ops_moar.so
7f65849f8000-7f65849f9000 r--p 00005000 fd​:00 1705219
/home/jdv/rakudo/install/share/perl6/runtime/dynext/libperl6_ops_moar.so
7f65849f9000-7f65849fa000 rw-p 00006000 fd​:00 1705219
/home/jdv/rakudo/install/share/perl6/runtime/dynext/libperl6_ops_moar.so
7f65849fa000-7f6584a20000 r--p 00000000 fd​:00 1705205
/home/jdv/rakudo/install/share/nqp/lib/Perl6/Optimizer.moarvm
7f6584a20000-7f6584a25000 r--p 00000000 fd​:00 1705207
/home/jdv/rakudo/install/share/nqp/lib/Perl6/Compiler.moarvm
7f6584a25000-7f6584aa6000 rw-p 00000000 00​:00 0
7f6584aa6000-7f6584af2000 r--p 00000000 fd​:00 1705201
/home/jdv/rakudo/install/share/nqp/lib/Perl6/World.moarvm
7f6584af2000-7f6584b02000 r--p 00000000 fd​:00 1705203
/home/jdv/rakudo/install/share/nqp/lib/Perl6/Ops.moarvm
7f6584b02000-7f6584be4000 r--p 00000000 fd​:00 1705204
/home/jdv/rakudo/install/share/nqp/lib/Perl6/Actions.moarvm
7f6584be4000-7f6584c1e000 r--p 00000000 fd​:00 1705195
/home/jdv/rakudo/install/share/nqp/lib/NQPP5QRegex.moarvm
7f6584c1e000-7f6584fb7000 r--p 00000000 fd​:00 1705202
/home/jdv/rakudo/install/share/nqp/lib/Perl6/Grammar.moarvm
7f6584fb7000-7f65853b8000 rw-p 00000000 00​:00 0
7f65853b8000-7f65853bb000 r-xp 00000000 fd​:00 1972990
/usr/lib64/libdl-2.20.so
7f65853bb000-7f65855ba000 ---p 00003000 fd​:00 1972990
/usr/lib64/libdl-2.20.so
7f65855ba000-7f65855bb000 r--p 00002000 fd​:00 1972990
/usr/lib64/libdl-2.20.so
7f65855bb000-7f65855bc000 rw-p 00003000 fd​:00 1972990
/usr/lib64/libdl-2.20.so
7f65855bc000-7f65855c3000 r-xp 00000000 fd​:00 1973518
/usr/lib64/librt-2.20.so
7f65855c3000-7f65857c2000 ---p 00007000 fd​:00 1973518
/usr/lib64/librt-2.20.so
7f65857c2000-7f65857c3000 r--p 00006000 fd​:00 1973518
/usr/lib64/librt-2.20.so
7f65857c3000-7f65857c4000 rw-p 00007000 fd​:00 1973518
/usr/lib64/librt-2.20.so
7f65857c4000-7f65857db000 r-xp 00000000 fd​:00 1973412
/usr/lib64/libpthread-2.20.so
7f65857db000-7f65859da000 ---p 00017000 fd​:00 1973412
/usr/lib64/libpthread-2.20.so
7f65859da000-7f65859db000 r--p 00016000 fd​:00 1973412
/usr/lib64/libpthread-2.20.so
7f65859db000-7f65859dc000 rw-p 00017000 fd​:00 1973412
/usr/lib64/libpthread-2.20.so
7f65859dc000-7f65859e0000 rw-p 00000000 00​:00 0
7f65859e0000-7f6585ae7000 r-xp 00000000 fd​:00 1973013
/usr/lib64/libm-2.20.so
7f6585ae7000-7f6585ce6000 ---p 00107000 fd​:00 1973013
/usr/lib64/libm-2.20.so
7f6585ce6000-7f6585ce7000 r--p 00106000 fd​:00 1973013
/usr/lib64/libm-2.20.so
7f6585ce7000-7f6585ce8000 rw-p 00107000 fd​:00 1973013
/usr/lib64/libm-2.20.so
7f6585ce8000-7f6585e9b000 r-xp 00000000 fd​:00 1972880
/usr/lib64/libc-2.20.so
7f6585e9b000-7f658609b000 ---p 001b3000 fd​:00 1972880
/usr/lib64/libc-2.20.so
7f658609b000-7f658609f000 r--p 001b3000 fd​:00 1972880
/usr/lib64/libc-2.20.so
7f658609f000-7f65860a1000 rw-p 001b7000 fd​:00 1972880
/usr/lib64/libc-2.20.so
7f65860a1000-7f65860a5000 rw-p 00000000 00​:00 0
7f65860a5000-7f6586464000 r-xp 00000000 fd​:00 1704742
/home/jdv/rakudo/install/lib/libmoar.so
7f6586464000-7f6586664000 ---p 003bf000 fd​:00 1704742
/home/jdv/rakudo/install/lib/libmoar.so
7f6586664000-7f65866fe000 r--p 003bf000 fd​:00 1704742
/home/jdv/rakudo/install/lib/libmoar.so
7f65866fe000-7f6586710000 rw-p 00459000 fd​:00 1704742
/home/jdv/rakudo/install/lib/libmoar.so
7f6586710000-7f6586711000 rw-p 00000000 00​:00 0
7f6586711000-7f6586732000 r-xp 00000000 fd​:00 1967760
/usr/lib64/ld-2.20.so
7f6586732000-7f6586736000 r-xp 00000000 00​:00 0
7f6586736000-7f658673b000 r--p 00000000 fd​:00 1705200
/home/jdv/rakudo/install/share/nqp/lib/Perl6/ModuleLoader.moarvm
7f658673b000-7f6586750000 r--p 00000000 fd​:00 1705206
/home/jdv/rakudo/install/share/nqp/lib/Perl6/Pod.moarvm
7f6586750000-7f6586756000 r-xp 00000000 00​:00 0
7f6586756000-7f6586771000 r--p 00000000 fd​:00 1704802
/home/jdv/rakudo/install/share/nqp/lib/MASTOps.moarvm
7f6586771000-7f65867e5000 r--p 00000000 fd​:00 1704804
/home/jdv/rakudo/install/share/nqp/lib/QAST.moarvm
7f65867e5000-7f658683b000 r--p 00000000 fd​:00 1704801
/home/jdv/rakudo/install/share/nqp/lib/NQPHLL.moarvm
7f658683b000-7f6586852000 r--p 00000000 fd​:00 1704799
/home/jdv/rakudo/install/share/nqp/lib/QASTNode.moarvm
7f6586852000-7f6586876000 r--p 00000000 fd​:00 1704800
/home/jdv/rakudo/install/share/nqp/lib/QRegex.moarvm
7f6586876000-7f65868d8000 r--p 00000000 fd​:00 1705185
/home/jdv/rakudo/install/share/nqp/lib/NQPP6QRegex.moarvm
7f65868d8000-7f65868ec000 r--p 00000000 fd​:00 1704796
/home/jdv/rakudo/install/share/nqp/lib/nqpmo.moarvm
7f65868ec000-7f6586912000 rw-p 00000000 00​:00 0
7f6586912000-7f6586913000 r-xp 00000000 00​:00 0
7f6586913000-7f658691f000 r--p 00000000 fd​:00 1704803
/home/jdv/rakudo/install/share/nqp/lib/MASTNodes.moarvm
7f658691f000-7f658692b000 r--p 00000000 fd​:00 1704798
/home/jdv/rakudo/install/share/nqp/lib/NQPCORE.setting.moarvm
7f658692b000-7f658692e000 r--p 00000000 fd​:00 1704797
/home/jdv/rakudo/install/share/nqp/lib/ModuleLoader.moarvm
7f658692e000-7f6586931000 r--p 00000000 fd​:00 1705216
/home/jdv/rakudo/install/share/perl6/runtime/perl6.moarvm
7f6586931000-7f6586932000 rw-p 00000000 00​:00 0
7f6586932000-7f6586933000 r--p 00021000 fd​:00 1967760
/usr/lib64/ld-2.20.so
7f6586933000-7f6586934000 rw-p 00022000 fd​:00 1967760
/usr/lib64/ld-2.20.so
7f6586934000-7f6586935000 rw-p 00000000 00​:00 0
7fff1823d000-7fff1825e000 rwxp 00000000 00​:00 0
[stack]
7fff1825e000-7fff1825f000 rw-p 00000000 00​:00 0
7fff18347000-7fff18349000 r--p 00000000 00​:00 0
[vvar]
7fff18349000-7fff1834b000 r-xp 00000000 00​:00 0
[vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00​:00 0
[vsyscall]
Aborted (core dumped)
[jdv@​wieldy ~]$ perl6 test_grammar_n_threads.p6
*** Error in `/home/jdv/rakudo/install/bin/moar'​: double free or
corruption (fasttop)​: 0x0000000005b4b8a0 ***
Segmentation fault (core dumped)
[jdv@​wieldy ~]$

From @jnthn

On Wed Aug 03 17​:07​:49 2016, jdv79 wrote​:

[jdv@​wieldy ~]$ perl6 test_grammar_n_threads.p6
Use of uninitialized value $!made of type Any in string context
Any of .^name, .perl, .gist, or .say can stringify undefined things,
if
needed.Use of uninitialized value $!made of type Any in string context
Any of .^name, .perl, .gist, or .say can stringify undefined things,
if
needed. in block at

This one I've managed to hunt down and fix. It's covered by a new test in S17-promise/start.t.

[jdv@​wieldy ~]$ perl6 test_grammar_n_threads.p6
*** Error in `/home/jdv/rakudo/install/bin/moar'​: double free or
corruption (fasttop)​: 0x000000000533c8a0 ***
======= Backtrace​: =========
/lib64/libc.so.6(+0x77d9e)[0x7f6585d5fd9e]
/lib64/libc.so.6(cfree+0x5b5)[0x7f6585d6b9f5]
//home/jdv/rakudo/install/lib/libmoar.so(MVM_interp_run+0x13b83)[0x7f658620d813]
//home/jdv/rakudo/install/lib/libmoar.so(+0x1774be)[0x7f658621c4be]
//home/jdv/rakudo/install/lib/libmoar.so(+0x23cf17)[0x7f65862e1f17]
/lib64/libpthread.so.0(+0x752a)[0x7f65857cb52a]
/lib64/libc.so.6(clone+0x6d)[0x7f6585de822d]

This one I've only managed to tickle once out of a hundred runs, and not with exactly that backtrace either. Will have to look into it a bit further.

/jnthn

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

From @jnthn

On Wed, 19 Oct 2016 07​:54​:05 -0700, jnthn@​jnthn.net wrote​:

[jdv@​wieldy ~]$ perl6 test_grammar_n_threads.p6
*** Error in `/home/jdv/rakudo/install/bin/moar'​: double free or
corruption (fasttop)​: 0x000000000533c8a0 ***
======= Backtrace​: =========
/lib64/libc.so.6(+0x77d9e)[0x7f6585d5fd9e]
/lib64/libc.so.6(cfree+0x5b5)[0x7f6585d6b9f5]
//home/jdv/rakudo/install/lib/libmoar.so(MVM_interp_run+0x13b83)[0x7f658620d813]
//home/jdv/rakudo/install/lib/libmoar.so(+0x1774be)[0x7f658621c4be]
//home/jdv/rakudo/install/lib/libmoar.so(+0x23cf17)[0x7f65862e1f17]
/lib64/libpthread.so.0(+0x752a)[0x7f65857cb52a]
/lib64/libc.so.6(clone+0x6d)[0x7f6585de822d]

This one I've only managed to tickle once out of a hundred runs, and
not with exactly that backtrace either. Will have to look into it a
bit further.

dogbert17++ managed to get some useful backtraces out of it, one of which pointed directly to the problem so I could fix it. Now the SEGV doesn't seem to happen even in hundreds of runs (must have reached into the thousands of runs). Added a test of a golf of the issue to S17-promise/start.t.

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