[PATCH] Add some parallel_for_each tests

[Tom Tromey <tom@tromey.com>]

This adds a few tests of parallel_for_each, primarily testing that
different settings for the number of threads will work.  This helps
address an issue that Tom de Vries pointed out in the DWARF scanner
rewrite series -- that a change to parallel_for_each introduced a
regression here.
---
 gdb/Makefile.in                        |  1 +
 gdb/unittests/parallel-for-selftests.c | 86 ++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100644 gdb/unittests/parallel-for-selftests.c

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 73a1bf83c85..320d3326a81 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -456,6 +456,7 @@ SELFTESTS_SRCS = \
 	unittests/offset-type-selftests.c \
 	unittests/observable-selftests.c \
 	unittests/optional-selftests.c \
+	unittests/parallel-for-selftests.c \
 	unittests/parse-connection-spec-selftests.c \
 	unittests/ptid-selftests.c \
 	unittests/main-thread-selftests.c \
diff --git a/gdb/unittests/parallel-for-selftests.c b/gdb/unittests/parallel-for-selftests.c
new file mode 100644
index 00000000000..7f61b709fa7
--- /dev/null
+++ b/gdb/unittests/parallel-for-selftests.c
@@ -0,0 +1,86 @@
+/* Self tests for parallel_for_each
+
+   Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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 "defs.h"
+#include "gdbsupport/selftest.h"
+#include "gdbsupport/parallel-for.h"
+#include "gdbsupport/thread-pool.h"
+
+#if CXX_STD_THREAD
+
+namespace selftests {
+namespace parallel_for {
+
+struct save_restore_n_threads
+{
+  save_restore_n_threads ()
+    : n_threads (gdb::thread_pool::g_thread_pool->thread_count ())
+  {
+  }
+
+  ~save_restore_n_threads ()
+  {
+    gdb::thread_pool::g_thread_pool->set_thread_count (n_threads);
+  }
+
+  int n_threads;
+};
+
+static void
+test (int n_threads)
+{
+  save_restore_n_threads saver;
+  gdb::thread_pool::g_thread_pool->set_thread_count (n_threads);
+
+#define NUMBER 10000
+
+  std::atomic<int> counter = 0;
+  gdb::parallel_for_each (0, NUMBER,
+			  [&] (int start, int end)
+			  {
+			    counter += end - start;
+			  });
+
+  SELF_CHECK (counter == NUMBER);
+
+#undef NUMBER
+}
+
+static void
+test_n_threads ()
+{
+  test (0);
+  test (1);
+  test (3);
+}
+
+}
+}
+
+#endif /* CXX_STD_THREAD */
+
+void _initialize_parallel_for_selftests ();
+void
+_initialize_parallel_for_selftests ()
+{
+#ifdef CXX_STD_THREAD
+  selftests::register_test ("parallel_for",
+			    selftests::parallel_for::test_n_threads);
+#endif /* CXX_STD_THREAD */
+}
-- 
2.31.1