Fix data races in libyuv::TestCpuFlag().

Detect the compiler's support of C11 atomics, and use C11 atomics when
available.

Note that libyuv::MaskCpuFlags() is still not thread-safe.

BUG=libyuv:641
TEST= cpu_thread_test.cc adds a pthread based test
R=wangcheng@google.com

Change-Id: If05b1e16da833105a0159ed67ef20f4e61bc7abd
Reviewed-on: https://chromium-review.googlesource.com/510079
Commit-Queue: Frank Barchard <fbarchard@google.com>
Reviewed-by: Cheng Wang <wangcheng@google.com>

Android.mk

@@ -89,6 +89,7 @@ LOCAL_SRC_FILES := \
     unit_test/compare_test.cc     \
     unit_test/convert_test.cc     \
     unit_test/cpu_test.cc         \
+    unit_test/cpu_thread_test.cc  \
     unit_test/math_test.cc        \
     unit_test/planar_test.cc      \
     unit_test/rotate_argb_test.cc \

BUILD.gn

@@ -238,6 +238,7 @@ if (libyuv_include_tests) {
       "unit_test/compare_test.cc",
       "unit_test/convert_test.cc",
       "unit_test/cpu_test.cc",
+      "unit_test/cpu_thread_test.cc",
       "unit_test/math_test.cc",
       "unit_test/planar_test.cc",
       "unit_test/rotate_argb_test.cc",

README.chromium

@@ -1,6 +1,6 @@
 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 1656
+Version: 1657
 License: BSD
 License File: LICENSE
 

include/libyuv/cpu_id.h

@@ -59,7 +59,12 @@ int ArmCpuCaps(const char* cpuinfo_name);
 // returns non-zero if instruction set is detected
 static __inline int TestCpuFlag(int test_flag) {
   LIBYUV_API extern int cpu_info_;
-  return (!cpu_info_ ? InitCpuFlags() : cpu_info_) & test_flag;
+#ifdef __ATOMIC_RELAXED
+  int cpu_info = __atomic_load_n(&cpu_info_, __ATOMIC_RELAXED);
+#else
+  int cpu_info = cpu_info_;
+#endif
+  return (!cpu_info ? InitCpuFlags() : cpu_info) & test_flag;
 }
 
 // For testing, allow CPU flags to be disabled.

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 1656
+#define LIBYUV_VERSION 1657
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_

libyuv_test.gyp

@@ -39,6 +39,7 @@
         'unit_test/color_test.cc',
         'unit_test/convert_test.cc',
         'unit_test/cpu_test.cc',
+        'unit_test/cpu_thread_test.cc',
         'unit_test/math_test.cc',
         'unit_test/planar_test.cc',
         'unit_test/rotate_argb_test.cc',

source/compare_win.cc

@@ -14,7 +14,7 @@
 #include "libyuv/row.h"
 
 #if defined(_MSC_VER)
-#include <intrin.h>   // For __popcnt
+#include <intrin.h>  // For __popcnt
 #endif
 
 #ifdef __cplusplus

source/cpu_id.cc

@@ -43,6 +43,9 @@ extern "C" {
 #define SAFEBUFFERS
 #endif
 
+// cpu_info_ variable for SIMD instruction sets detected.
+LIBYUV_API int cpu_info_ = 0;
+
 // Low level cpuid for X86.
 #if (defined(_M_IX86) || defined(_M_X64) || defined(__i386__) || \
      defined(__x86_64__)) &&                                     \
@@ -192,10 +195,6 @@ LIBYUV_API SAFEBUFFERS int MipsCpuCaps(const char* cpuinfo_name,
   return 0;
 }
 
-// CPU detect function for SIMD instruction sets.
-LIBYUV_API
-int cpu_info_ = 0;  // cpu_info is not initialized yet.
-
 // Test environment variable for disabling CPU features. Any non-zero value
 // to disable. Zero ignored to make it easy to set the variable on/off.
 #if !defined(__native_client__) && !defined(_M_ARM)
@@ -215,7 +214,7 @@ static LIBYUV_BOOL TestEnv(const char*) {
 }
 #endif
 
-LIBYUV_API SAFEBUFFERS int InitCpuFlags(void) {
+static SAFEBUFFERS int GetCpuFlags(void) {
   int cpu_info = 0;
 #if !defined(__pnacl__) && !defined(__CLR_VER) && defined(CPU_X86)
   uint32 cpu_info0[4] = {0, 0, 0, 0};
@@ -321,14 +320,27 @@ LIBYUV_API SAFEBUFFERS int InitCpuFlags(void) {
     cpu_info = 0;
   }
   cpu_info |= kCpuInitialized;
-  cpu_info_ = cpu_info;
   return cpu_info;
 }
 
 // Note that use of this function is not thread safe.
 LIBYUV_API
 void MaskCpuFlags(int enable_flags) {
-  cpu_info_ = InitCpuFlags() & enable_flags;
+#ifdef __ATOMIC_RELAXED
+  __atomic_store_n(&cpu_info_, GetCpuFlags() & enable_flags, __ATOMIC_RELAXED);
+#else
+  cpu_info_ = GetCpuFlags() & enable_flags;
+#endif
+}
+
+LIBYUV_API
+int InitCpuFlags(void) {
+  MaskCpuFlags(-1);
+#ifdef __ATOMIC_RELAXED
+  return __atomic_load_n(&cpu_info_, __ATOMIC_RELAXED);
+#else
+  return cpu_info_;
+#endif
 }
 
 #ifdef __cplusplus

unit_test/cpu_thread_test.cc

@@ -0,0 +1,60 @@
+/*
+ *  Copyright 2017 The LibYuv Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS. All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <gtest/gtest.h>
+
+#include "libyuv/cpu_id.h"
+
+// TODO(fbarchard): Port to other platforms
+#if defined(__linux__)
+#define LIBYUV_HAVE_PTHREAD 1
+#endif
+
+#ifdef LIBYUV_HAVE_PTHREAD
+#include <pthread.h>
+#endif
+
+namespace libyuv {
+
+#ifdef LIBYUV_HAVE_PTHREAD
+void* ThreadMain(void* arg) {
+  int* flags = static_cast<int*>(arg);
+
+  *flags = TestCpuFlag(kCpuHasSSSE3);
+  return nullptr;
+}
+#endif  // LIBYUV_HAVE_PTHREAD
+
+// Call TestCpuFlag() from two threads. ThreadSanitizer should not report any
+// data race.
+TEST(LibYUVCpuThreadTest, TestCpuFlagMultipleThreads) {
+#ifdef LIBYUV_HAVE_PTHREAD
+  int cpu_flags1;
+  int cpu_flags2;
+  int ret;
+  pthread_t thread1;
+  pthread_t thread2;
+
+  MaskCpuFlags(0);  // Reset to 0 to allow auto detect.
+  ret = pthread_create(&thread1, nullptr, ThreadMain, &cpu_flags1);
+  ASSERT_EQ(ret, 0);
+  ret = pthread_create(&thread2, nullptr, ThreadMain, &cpu_flags2);
+  ASSERT_EQ(ret, 0);
+  ret = pthread_join(thread1, nullptr);
+  EXPECT_EQ(ret, 0);
+  ret = pthread_join(thread2, nullptr);
+  EXPECT_EQ(ret, 0);
+  EXPECT_EQ(cpu_flags1, cpu_flags2);
+#else
+  printf("pthread unavailable; Test skipped.");
+#endif  // LIBYUV_HAVE_PTHREAD
+}
+
+}  // namespace libyuv