Fix DisjConditions module to be thread-safe for perl >= 5.7.2.

Self-hashes of blessed references are not correctly transported
through thread creation.  This patch fixes that by recreating
the hashes upon thread creation with a CLONE special subroutine,
which is automatically invoked by new enough Perl versions.
* lib/Automake/DisjConditions.pm (CLONE): New special
subroutine to fix self hashes upon thread creation.
* lib/Automake/tests/Condition-t.pl: New, sister test to
Condition.pl, but spawns a new threads after each creation of a
new condition; skip test if perl is too old or ithreads are not
available.
* lib/Automake/tests/DisjConditions-t.pl: Likewise.
* lib/Automake/tests/Makefile.am (TESTS): Add them.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>

1 files changed, 20 insertions, 0 deletions

diff --git a/lib/Automake/DisjConditions.pm b/lib/Automake/DisjConditions.pm
index 1f09c0fd4..ae759e27c 100644
--- a/lib/Automake/DisjConditions.pm
+++ b/lib/Automake/DisjConditions.pm
@@ -192,6 +192,26 @@ sub new ($;@)
   return $self;
 }
 
+
+=item C<CLONE>
+
+Internal special subroutine to fix up the self hashes in
+C<%_disjcondition_singletons> upon thread creation.  C<CLONE> is invoked
+automatically with ithreads from Perl 5.7.2 or later, so if you use this
+module with earlier versions of Perl, it is not thread-safe.
+
+=cut
+
+sub CLONE
+{
+  foreach my $self (values %_disjcondition_singletons)
+    {
+      my %h = map { $_ => $_ } @{$self->{'conds'}};
+      $self->{'hash'} = \%h;
+    }
+}
+
+
 =item C<@conds = $set-E<gt>conds>
 
 Return the list of C<Condition> objects involved in C<$set>.