benchtests: Add pthread_once common-case test.

We have a single thread that runs a no-op initialization once and then
repeatedly runs checks of the initialization (i.e., an acquire load and
conditional jump) in a tight loop.  This gives us, on average, the
best-case latency of pthread_once (the initialization is the
exactly-once slow path, and we're not looking at initialization-related
synchronization overheads in this case).

1 files changed, 25 insertions, 0 deletions

diff --git a/benchtests/pthread_once-source.c b/benchtests/pthread_once-source.c
new file mode 100644
index 0000000000..5f98b0a3b3
--- /dev/null
+++ b/benchtests/pthread_once-source.c
@@ -0,0 +1,25 @@
+/* Measure pthread_once best-case latency (i.e., when already initialized.
+
+   Copyright (C) 2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+static pthread_once_t once = PTHREAD_ONCE_INIT;
+
+static void
+once_handler (void)
+{
+}