Add mi-threads-interrupt.exp test (PR 20039)

Add a new test for PR 20039.  The test spawns new threads, then tries to
interrupt, continue, and interrupt again.  This use case was fixed by
commit 5fe966540d in master, but gdb 7.11
is affected (so if you try it on the gdb-7.11-branch right now, the test
will fail).

New in v2, the test now handles mi-async on mode properly.  The failure
was specific to mi-async off, but I don't think it's bad to test the
same thing under async on mode.  I added a little hack when running in
async mode to work around bug 20045.

I also removed one continue/interrupt pair, as a single one was enough to
trigger the problem.

gdb/testsuite/ChangeLog:

	* gdb.mi/mi-threads-interrupt.c: New file.
	* gdb.mi/mi-threads-interrupt.exp: New file.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2016-05-18  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* gdb.mi/mi-threads-interrupt.c: New file.
+	* gdb.mi/mi-threads-interrupt.exp: New file.
+
 2016-05-17  Simon Marchi  <simon.marchi@ericsson.com>
 
 	PR gdb/18077

gdb/testsuite/gdb.mi/mi-threads-interrupt.c

@@ -0,0 +1,61 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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/>.  */
+
+#include <pthread.h>
+#include <unistd.h>
+
+#define NUM_THREADS 2
+
+static pthread_barrier_t barrier;
+
+static void *
+thread_func (void *v)
+{
+  int i;
+
+  pthread_barrier_wait (&barrier);
+
+  for (i = 0; i < 100; i++)
+    sleep (1);
+}
+
+static void
+all_threads_created (void)
+{
+}
+
+int
+main (void)
+{
+  int i;
+  pthread_t threads[NUM_THREADS];
+
+  /* +1 to account for the main thread */
+  pthread_barrier_init (&barrier, NULL, NUM_THREADS + 1);
+
+  for (i = 0; i < NUM_THREADS; i++)
+    pthread_create (&threads[i], NULL, thread_func, NULL);
+
+  pthread_barrier_wait (&barrier);
+
+  all_threads_created ();
+
+  for (i = 0; i < 100; i++)
+    sleep (1);
+
+  return 0;
+}

gdb/testsuite/gdb.mi/mi-threads-interrupt.exp

@@ -0,0 +1,69 @@
+# Copyright 2016 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/>.
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+standard_testfile
+
+if {[gdb_compile_pthreads "$srcdir/$subdir/$srcfile" $binfile executable {debug}] != "" } {
+    return -1
+}
+
+# This tests the resolution of PR 20039.
+#
+# With a multi-threaded inferior and with MI/all-stop, it was not possible
+# to interrupt it with ctrl-C after a continue.
+
+proc test_continue_interrupt { } {
+  global binfile
+  global async
+
+  gdb_exit
+  if {[mi_gdb_start]} {
+      continue
+  }
+
+  # Load the binary in gdb...
+  mi_gdb_load $binfile
+
+  # ... and run it.
+  #
+  # Note this test relies on mi_runto deleting the breakpoint.
+  # A step-over here would mask the bug.
+  mi_runto "all_threads_created"
+
+  # Consistency check.
+  mi_check_thread_states {"stopped" "stopped" "stopped"} "check thread states"
+
+  # Continue.
+  mi_send_resuming_command "exec-continue" "continue"
+
+  # Wait a bit to make sure all MI events are sent, before sending the
+  # interruption request.
+  sleep 1
+
+  # Send the interrupt request.
+  if { $async } {
+    mi_gdb_test "888-exec-interrupt" "888\\^done" "interrupt"
+  } else {
+    send_gdb "\003"
+  }
+
+  # Wait for the *stopped.
+  mi_expect_interrupt "interrupt reported"
+}
+
+test_continue_interrupt