Detecting global destruction in Perl

Question

I'd like to detect if my object is being DESTROY'd as part of global destruction, and print out a warning (as that'd clearly be an error and lead to data loss). The obvious way to do that would seem to be:

sub DESTROY {
    my $self = shift;
    # ⋮
    if (i_am_in_global_destruction()) {
        warn "I survived until global destruction";
    }
}

but I have been unable to find a good way to detect global destruction (instead of normal refcount hit 0 destruction).

By "good way", I mean not this, which though it works on 5.10.1 and 5.8.8, probably breaks the second someone gives it an odd glance:

sub DESTROY {
    $in_gd = 0;
    {
        local $SIG{__WARN__} = sub { $_[0] =~ /during global destruction\.$/ and $in_gd = 1 };
        warn "look, a warning";
    }
    if ($in_gd) {
        warn "I survived until global destruction";
    }
}'

Answer 1

There's a module Devel::GlobalDestruction that uses a tiny bit of XS to let you get at the global destruction flag directly.

Update: since perl 5.14.0 there is a global variable ${^GLOBAL_PHASE} that will be set to "DESTRUCT" during global destruction. You should still generally use Devel::GlobalDestruction, since it works with perls back to 5.6. When installing on a perl with ${^GLOBAL_PHASE} it will use the built-in feature and not even require a C compiler to build.

Answer 2

A solution that is good enough for me is to set a flag in an END block.

package Whatever;
our $_IN_GLOBAL_DESTRUCTION = 0;
END {
    $_IN_GLOBAL_DESTRUCTION = 1;
}