In Perl 5.8.0 the so-called "safe signals" were introduced. This means that Perl
no longer handles signals immediately but instead "between opcodes", when it is
safe to do so. The earlier immediate handling easily could corrupt the internal
state of Perl, resulting in mysterious crashes.

It's possible since perl 5.8.1 to globally disable this feature by using the
PERL_SIGNALS environment variables (as specified in "PERL_SIGNALS" in perlrun);
but there's no way to disable it locally, for a short period of time. That's
however something you might want to do, if, for example, your Perl program calls
a C routine that will potentially run for a long time and for which you want to
set a timeout.

This module therefore allows you to define UNSAFE_SIGNALS blocks in which
signals will be handled "unsafely".

WWW: https://metacpan.org/release/Perl-Unsafe-Signals