From 00aaea364501b3b0abe58dae461136159df1e356 Mon Sep 17 00:00:00 2001
From: Hans Boehm <hboehm@google.com>
Date: Tue, 19 Aug 2014 16:14:01 -0700
Subject: Fix, generalize stdatomic.h; improve test.

We seem to use this stdatomic.h sometimes, and slightly different prebuilts
at other times, making them all difficult to test, and making it unclear
which one we're testing.  This generalizes the bionic header so that it
can be used directly as the prebuilt header as well.  So long as they
don't diverge again, that should somewhat improve test coverage.

Use the correct builtin for atomic_is_lock_free.

Fix atomic_flag_init.

Turn on atomic tests even with __GLIBC__, since they now appear to pass.

Include uchar.h in stdatomic.h where needed.

Add a basic memory ordering test.

Fix bit-rotted comments in bionic tests makefile.

Change-Id: If6a14c1075b379395ba5d93357d56025c0ffab68
---
 tests/stdatomic_test.cpp | 85 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 80 insertions(+), 5 deletions(-)

(limited to 'tests/stdatomic_test.cpp')

diff --git a/tests/stdatomic_test.cpp b/tests/stdatomic_test.cpp
index 5e88c8801..222bd9c80 100644
--- a/tests/stdatomic_test.cpp
+++ b/tests/stdatomic_test.cpp
@@ -14,11 +14,10 @@
  * limitations under the License.
  */
 
-#include <gtest/gtest.h>
-
-#if !defined(__GLIBC__) /* TODO: fix our prebuilt toolchains! */
-
 #include <stdatomic.h>
+#include <gtest/gtest.h>
+#include <pthread.h>
+#include <stdint.h>
 
 TEST(stdatomic, LOCK_FREE) {
   ASSERT_TRUE(ATOMIC_BOOL_LOCK_FREE);
@@ -167,4 +166,80 @@ TEST(stdatomic, atomic_fetch_and) {
   ASSERT_EQ(0x002, atomic_load(&i));
 }
 
-#endif
+// And a rudimentary test of acquire-release memory ordering:
+
+constexpr static uint_least32_t BIG = 10000000ul; // Assumed even below.
+
+struct three_atomics {
+  atomic_uint_least32_t x;
+  char a[123];  // Everything in different cache lines,
+                // increase chance of compiler getting alignment wrong.
+  atomic_uint_least32_t y;
+  char b[4013];
+  atomic_uint_least32_t z;
+};
+
+// Very simple acquire/release memory ordering sanity check.
+static void* writer(void* arg) {
+  three_atomics* a = reinterpret_cast<three_atomics*>(arg);
+  for (uint_least32_t i = 0; i <= BIG; i+=2) {
+    atomic_store_explicit(&a->x, i, memory_order_relaxed);
+    atomic_store_explicit(&a->z, i, memory_order_relaxed);
+    atomic_store_explicit(&a->y, i, memory_order_release);
+    atomic_store_explicit(&a->x, i+1, memory_order_relaxed);
+    atomic_store_explicit(&a->z, i+1, memory_order_relaxed);
+    atomic_store_explicit(&a->y, i+1, memory_order_release);
+  }
+  return 0;
+}
+
+static void* reader(void* arg) {
+  three_atomics* a = reinterpret_cast<three_atomics*>(arg);
+  uint_least32_t xval = 0, yval = 0, zval = 0;
+  size_t repeat = 0;
+  size_t repeat_limit = 1000;
+  while (yval != BIG + 1) {
+    yval = atomic_load_explicit(&a->y, memory_order_acquire);
+    zval = atomic_load_explicit(&a->z, memory_order_relaxed);
+    xval = atomic_load_explicit(&a->x, memory_order_relaxed);
+    // If we see a given value of y, the immediately preceding
+    // stores to z and x, or later ones, should also be visible.
+    if (zval < yval) {
+      // Cant just ASSERT, since we are in a non-void function.
+      ADD_FAILURE() << "acquire-release ordering violation: "
+                    << zval << " < " << yval << ", " << xval << "\n";
+      return 0; // Only report once.
+    }
+    if (xval < yval) {
+      // Cant just ASSERT, since we are in a non-void function.
+      ADD_FAILURE() << "acquire-release ordering violation: "
+                    << xval << " < " << yval << ", " << zval <<  "\n";
+      return 0; // Only report once.
+    }
+    if (repeat < repeat_limit) ++repeat;
+  }
+  // The following assertion is not technically guaranteed to hold.
+  // But if it fails to hold, this test was useless, and we have a
+  // serious scheduling issue that we should probably know about.
+  EXPECT_EQ(repeat, repeat_limit);
+  return 0;
+}
+
+TEST(stdatomic, ordering) {
+  // Run a memory ordering sanity test.
+  void* result;
+  three_atomics a;
+  atomic_init(&a.x, 0ul);
+  atomic_init(&a.y, 0ul);
+  atomic_init(&a.z, 0ul);
+  pthread_t t1,t2;
+  ASSERT_EQ(0, pthread_create(&t1, 0, reader, &a));
+  ASSERT_EQ(0, pthread_create(&t2, 0, writer, &a));
+  ASSERT_EQ(0, pthread_join(t1, &result));
+  EXPECT_EQ(0, result);
+  ASSERT_EQ(0, pthread_join(t2, &result));
+  EXPECT_EQ(0, result);
+  EXPECT_EQ(atomic_load_explicit(&a.x, memory_order_consume), BIG + 1);
+  EXPECT_EQ(atomic_load_explicit(&a.y, memory_order_seq_cst), BIG + 1);
+  EXPECT_EQ(atomic_load(&a.z), BIG + 1);
+}
-- 
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