add direct tests for the bug reported in #22487

This was fixed by 85e9706 but the test only checked the sanity of the
saved main thread thread id.

Tested locally for failure by disarming the change in
Perl_csighandler3.

Author: tonycoz

ext/XS-APItest/APItest.pm

@@ -4,7 +4,7 @@ use strict;
 use warnings;
 use Carp;
 
-our $VERSION = '1.43';
+our $VERSION = '1.44';
 
 require XSLoader;
 

ext/XS-APItest/APItest.xs

@@ -1601,6 +1601,17 @@ destruct_test(pTHX_ void *p) {
     warn("In destruct_test: %" SVf "\n", (SV*)p);
 }
 
+#if defined(USE_ITHREADS) && !defined(WIN32)
+
+static void *
+signal_thread_start(void *arg) {
+  PERL_UNUSED_ARG(arg);
+  raise(SIGUSR1);
+  return NULL;
+}
+
+#endif
+
 #ifdef PERL_USE_HWM
 #  define hwm_checks_enabled() true
 #else
@@ -4367,6 +4378,21 @@ CODE:
 OUTPUT:
     RETVAL
 
+pthread_t
+make_signal_thread()
+CODE:
+    if (pthread_create(&RETVAL, NULL, signal_thread_start, NULL) != 0)
+        XSRETURN_EMPTY;
+OUTPUT:
+    RETVAL
+
+int
+join_signal_thread(pthread_t tid)
+CODE:
+    RETVAL = pthread_join(tid, NULL);
+OUTPUT:
+    RETVAL
+
 #  endif /* ifndef WIN32 */
 
 #endif /* USE_ITHREADS */

ext/XS-APItest/t/thread.t

@@ -2,15 +2,15 @@
 use warnings;
 use strict;
 use Test2::IPC;
-use Test2::Tools::Basic;
+use Test2::V0;
 use Config;
 
 BEGIN {
     skip_all "Not pthreads or is win32"
       if !$Config{usethreads} || $^O eq "MSWin32";
 }
 
-use XS::APItest qw(thread_id_matches);
+use XS::APItest qw(thread_id_matches make_signal_thread join_signal_thread);
 
 ok(thread_id_matches(),
    "check main thread id saved and is current thread");
@@ -38,4 +38,34 @@ SKIP:
     }
 }
 
+{
+    my $saw_signal;
+    local $SIG{USR1} = sub { ++$saw_signal };
+    my $pid = make_signal_thread();
+    join_signal_thread($pid);
+    ok($saw_signal, "saw signal sent to non-perl thread");
+}
+
+{
+    $Config{d_fork}
+      or skip "Need fork", 1;
+    my $pid = fork;
+    defined $pid
+      or skip "Fork failed", 1;
+    if ($pid == 0) {
+        # ensure the main thread saved is valid after fork
+        my $saw_signal;
+        local $SIG{USR1} = sub { ++$saw_signal };
+        my $pid = make_signal_thread();
+        join_signal_thread($pid);
+        ok($saw_signal, "saw signal sent to non-perl thread in child");
+        exit 0;
+    }
+    else {
+        is(waitpid($pid, 0), $pid, "wait child");
+        # catches the child segfaulting for example
+        is($?, 0, "child success");
+    }
+}
+
 done_testing();

ext/XS-APItest/typemap

@@ -3,12 +3,27 @@ XS::APItest::PtrTable		T_PTROBJ
 const WCHAR *			WPV
 U8 *		                T_PV
 
+pthread_t			T_THREADID
+
 INPUT
 
 WPV
         $var = ($type)SvPV_nolen($arg);
 
+T_THREADID
+        {
+          STRLEN len;
+          const char *pv = SvPVbyte($arg, len);
+          if (len != sizeof(pthread_t))
+            croak(\"Bad thread id for $arg\");
+          Copy(pv, &$var, 1, pthread_t);
+        }
+
 OUTPUT
 
 WPV
         sv_setpvn($arg, (const char *)($var), sizeof(WCHAR) * (1+wcslen($var)));
+
+T_THREADID
+        sv_setpvn($arg, (const char *)&($var), sizeof($var));
+        SvUTF8_off($arg);