threads.xs: don't Copy() null pointer

iabyn · iabyn · commit 97fcda75b598 · 2017-09-04T11:09:06.000+01:00
If a thread is created with no parameters, e.g.

    use threads;
    threads-&gt;new(sub {})-&gt;join;

Then it tries to Copy() zero parameters to AvARRAY(params), which is null.
Since v5.27.3-31-gf14cf36, this triggers an assert failure, so threaded
builds have been badly broken.
diff --git a/dist/threads/lib/threads.pm b/dist/threads/lib/threads.pm
@@ -5,7 +5,7 @@ use 5.008;
 use strict;
 use warnings;
 
-our $VERSION = '2.17';
+our $VERSION = '2.18';
 my $XS_VERSION = $VERSION;
 $VERSION = eval $VERSION;
 
diff --git a/dist/threads/threads.xs b/dist/threads/threads.xs
@@ -870,15 +870,18 @@ S_ithread_create(
            reallocated (and hence move) as a side effect of calls to
            perl_clone() and sv_dup_inc(). Hence copy the parameters
            somewhere under our control first, before duplicating.  */
+        if (num_params) {
 #if (PERL_VERSION > 8)
-        Copy(parent_perl->Istack_base + params_start, array, num_params, SV *);
+            Copy(parent_perl->Istack_base + params_start, array, num_params, SV *);
 #else
-        Copy(parent_perl->Tstack_base + params_start, array, num_params, SV *);
+            Copy(parent_perl->Tstack_base + params_start, array, num_params, SV *);
 #endif
-        while (num_params--) {
-            *array = sv_dup_inc(*array, clone_param);
-            ++array;
+            while (num_params--) {
+                *array = sv_dup_inc(*array, clone_param);
+                ++array;
+            }
         }
+
 #if (PERL_VERSION > 13) || (PERL_VERSION == 13 && PERL_SUBVERSION > 1)
         Perl_clone_params_del(clone_param);
 #endif
