util: Add util_call_once for optimize call to util_call_once_with_context out for hot path

For hot path, there is only need to a load instruction to load if initialized are true now,
So the extra cost is minimal.

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Acked-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18323>

src/util/tests/u_call_once_test.cpp

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2022 Yonggang Luo
+ * SPDX-License-Identifier: MIT
+ *
+ * Testing u_call_once.h
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <gtest/gtest.h>
+
+#include "c11/threads.h"
+#include "util/u_atomic.h"
+#include "util/u_call_once.h"
+
+#define NUM_DEBUG_TEST_THREAD 8
+
+static void update_x(int *x) {
+   p_atomic_inc(x);
+}
+
+static int xC;
+static void update_x_global(void)
+{
+   update_x(&xC);
+}
+
+static int test_call_once(void *_state)
+{
+   static int xA = 0;
+   {
+      static once_flag once = ONCE_FLAG_INIT;
+      for (int i = 0; i < 100; i += 1) {
+         util_call_once_data_slow(&once, (util_call_once_data_func)update_x, &xA);
+      }
+   }
+
+   static int xB = 0;
+   {
+      static util_once_flag once = UTIL_ONCE_FLAG_INIT;
+      for (int i = 0; i < 100; i += 1) {
+         util_call_once_data(&once, (util_call_once_data_func)update_x, &xB);
+      }
+   }
+   {
+      static util_once_flag once = UTIL_ONCE_FLAG_INIT;
+      for (int i = 0; i < 100; i += 1) {
+         util_call_once(&once, update_x_global);
+      }
+   }
+   EXPECT_EQ(xA, 1);
+   EXPECT_EQ(xB, 1);
+   EXPECT_EQ(xC, 1);
+   return 0;
+}
+
+TEST(UtilCallOnce, Multithread)
+{
+   thrd_t threads[NUM_DEBUG_TEST_THREAD];
+   for (unsigned i = 0; i < NUM_DEBUG_TEST_THREAD; i++) {
+        thrd_create(&threads[i], test_call_once, NULL);
+   }
+   for (unsigned i = 0; i < NUM_DEBUG_TEST_THREAD; i++) {
+      int ret;
+      thrd_join(threads[i], &ret);
+   }
+}