END blocks not executed after SIGINT interrupts blocked flush().

[rxxrc]

To: [email protected]
Subject: END blocks not executed sometimes on SIGINT.
From: [email protected]
Message-Id: [email protected]
Reply-To: [email protected]

This is a bug report for perl from [email protected],
generated with the help of perlbug 1.41 running under perl 5.30.1.

---

For some reason END blocks are not executed if

1. the program is blocked in a flush() call because a pipe buffer is
   full
2. the block is interrupted by a SIGINT (possibly other signals; I haven't
   tested)
3. the SIGINT is caught with a $SIG{INT} handler which calls exit()

If the program is blocked in any other way the END block is run as expected.

Minimal(-ish) demonstration:

#!/usr/bin/env perl

use strict;
use warnings;

$SIG{INT} = sub {
    print "\nSIGINT received\n";
    exit 2;
};

END {
    print "END BLOCK\n";
}

my $child_pid = open my $child_handle, '|-', "sleep 9999"
    or die "fork failed: $!\n";

# As soon as this overflows the 16-bit mark, and hence our writes start
# blocking on the pipe buffer, perl no longer seems to run END blocks on
# SIGINT?
my $count = 65537;

for (1..$count) {
    print{$child_handle} "\n" or die "print failed: $!\n";
    # SIGINT while this is blocked (because the pipe buffer is full) triggers
    # the $SIG{INT} trap and exits the program, but does not execute the
    # END block.
    $child_handle->flush or die "flush failed: $!\n";
}
print "printing done\n";

# SIGINT while *this* is blocked (if we didn't fill the pipe buffer) triggers
# the SIGINT handler but also runs the END block.
waitpid $child_pid, 0;

Perl Info

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl 5.30.1:

Configured by builduser at Mon Nov 11 19:16:46 CET 2019.

Summary of my perl5 (revision 5 version 30 subversion 1) configuration:

  Platform:
    osname=linux
    osvers=5.3.8-arch1-1
    archname=x86_64-linux-thread-multi
    uname='linux flo-64 5.3.8-arch1-1 #1 smp preempt @1572357769 x86_64 gnulinux '
    config_args='-des -Dusethreads -Duseshrplib -Doptimize=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt -Dprefix=/usr -Dvendorprefix=/usr -Dprivlib=/usr/share/perl5/core_perl -Darchlib=/usr/lib/perl5/5.30/core_perl -Dsitelib=/usr/share/perl5/site_perl -Dsitearch=/usr/lib/perl5/5.30/site_perl -Dvendorlib=/usr/share/perl5/vendor_perl -Dvendorarch=/usr/lib/perl5/5.30/vendor_perl -Dscriptdir=/usr/bin/core_perl -Dsitescript=/usr/bin/site_perl -Dvendorscript=/usr/bin/vendor_perl -Dinc_version_list=none -Dman1ext=1perl -Dman3ext=3perl -Dcccdlflags='-fPIC' -Dlddlflags=-shared -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -Dldflags=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'
    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='cc'
    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt'
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='9.2.0'
    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='cc'
    ldflags ='-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include-fixed /usr/lib /lib/../lib /usr/lib/../lib /lib /lib64 /usr/lib64
    libs=-lpthread -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.30.so
    so=so
    useshrplib=true
    libperl=libperl.so
    gnulibc_version='2.30'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.30/core_perl/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -L/usr/local/lib -fstack-protector-strong'


---
@INC for perl 5.30.1:
    /usr/lib/perl5/5.30/site_perl
    /usr/share/perl5/site_perl
    /usr/lib/perl5/5.30/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib/perl5/5.30/core_perl
    /usr/share/perl5/core_perl

---
Environment for perl 5.30.1:
    HOME=/rxxrc
    LANG=en_AU.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/rxxrc/bin:/rxxrc/.cargo/bin:/rxxrc/bin:/rxxrc/.cargo/bin:/rxxrc/bin:/rxxrc/.cargo/bin
    PERL_BADLANG (unset)
    SHELL=/bin/bash