t/op/threads.t fails occasionally on cygwin

[tonycoz]

Module:none

Description

t/op/threads.t occasionally fails on cygwin with an unexpected output error, while testing with blead I saw two slightly different failure outputs:

t/op/threads ... 1..30
ok 1 - delete() under threads
ok 2 - weaken ref under threads
ok 3 - weaken ref \#2 under threads
# parent 17232: continue
# kid 1 before sort
# parent 17232: continue
# parent 17232: waiting for join
# kid 2 before sort
ds
FAILED--unexpected output at test 3
Failed 1 test out of 1, 0.00% okay.
        op/threads.t

and

t/op/threads ... 1..30
ok 1 - delete() under threads
ok 2 - weaken ref under threads
ok 3 - weaken ref \#2 under threads
# parent 17820: continue
# kid 1 before sort
# parent 17820: continue
# kid 2 before sort
# parent 17820: waiting for join
# kid 1 after sort, sleeping 1
ds# kid 2 after sort, sleeping 1
FAILED--unexpected output at test 3
Failed 1 test out of 1, 0.00% okay.
        op/threads.t

In earlier tests on a slightly different build the extra text was er th instead ds.

Steps to Reproduce

Build perl on cygwin:

./Configure -des -Dusedevel -DDEBUGGING && make -j3 test-prep

Run op/threads until it fails:

cd t ; while ./perl TEST -v op/threads.t ; do echo foo ; done

Expected behavior

The test passes, no extra output is produced.

Perl configuration

Summary of my perl5 (revision 5 version 31 subversion 7) configuration:
  Commit id: 6162bc4e7a5d555eed76378d5ade716c7d4276e1
  Platform:
    osname=cygwin
    osvers=3.0.7(0.33853)
    archname=cygwin-thread-multi
    uname='cygwin_nt-10.0 phobos 3.0.7(0.33853) 2019-04-30 18:08 x86_64 cygwin '
    config_args='-des -Dusedevel -DDEBUGGING'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='gcc'
    ccflags ='-DPERL_USE_SAFE_PUTENV -U__STRICT_ANSI__ -D_GNU_SOURCE -fwrapv -DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector-strong -D_FORTIFY_SOURCE=2'
    optimize='-O3 -g'
    cppflags='-DPERL_USE_SAFE_PUTENV -U__STRICT_ANSI__ -D_GNU_SOURCE -fwrapv -DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector-strong'
    ccversion=''
    gccversion='7.4.0'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='g++'
    ldflags =' -Wl,--enable-auto-import -Wl,--export-all-symbols -Wl,--enable-auto-image-base -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/lib /usr/lib/gcc/x86_64-pc-cygwin/7.4.0/../../../../lib/../include/w32api /usr/local/lib /lib
    libs=-lpthread -ldl
    perllibs=-lpthread -ldl
    libc=/usr/lib/libc.a
    so=dll
    useshrplib=true
    libperl=cygperl5_31_7.dll
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=dll
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags=' --shared  -Wl,--enable-auto-import -Wl,--export-all-symbols -Wl,--enable-auto-image-base -L/usr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl):
  Compile-time options:
    DEBUGGING
    HAS_TIMES
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_IMPLICIT_CONTEXT
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_TRACK_MEMPOOL
    PERL_USE_DEVEL
    PERL_USE_SAFE_PUTENV
    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
    USE_THREAD_SAFE_LOCALE
  Built under cygwin
  Compiled at Dec 16 2019 11:20:50
  @INC:
    lib
    /usr/local/lib/perl5/site_perl/5.31.7/cygwin-thread-multi
    /usr/local/lib/perl5/site_perl/5.31.7
    /usr/local/lib/perl5/5.31.7/cygwin-thread-multi
    /usr/local/lib/perl5/5.31.7