Testcase for attaching in non-stop mode

This adds a testcase exercising attaching to a multi-threaded process,
in all combinations of:

  - set non-stop on/off
  - maint target non-stop off/on
  - "attach" vs "attach &"

This exercises the bugs fixed in the two previous patches.

gdb/testsuite/ChangeLog:

	* gdb.threads/attach-non-stop.c: New file.
	* gdb.threads/attach-non-stop.exp: New file.

1 files changed, 58 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.threads/attach-non-stop.c b/gdb/testsuite/gdb.threads/attach-non-stop.c
new file mode 100644
index 0000000..23a8b25
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/attach-non-stop.c
@@ -0,0 +1,58 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2021 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <pthread.h>
+#include <unistd.h>
+
+/* Number of threads we'll create.  */
+static const int n_threads = 10;
+
+/* Entry point for threads.  Loops forever.  */
+
+void *
+thread_func (void *arg)
+{
+  while (1)
+    sleep (1);
+
+  return NULL;
+}
+
+int
+main (int argc, char **argv)
+{
+  int i;
+
+  alarm (30);
+
+  /* Spawn the test threads.  */
+  for (i = 0; i < n_threads; ++i)
+    {
+      pthread_t child;
+      int rc;
+
+      rc = pthread_create (&child, NULL, thread_func, NULL);
+      assert (rc == 0);
+    }
+
+  while (1)
+    sleep (1);
+
+  return 0;
+}