1 files changed, 111 insertions, 0 deletions
diff --git a/media/libvpx/libvpx/vpx_util/vpx_atomics.h b/media/libvpx/libvpx/vpx_util/vpx_atomics.h
new file mode 100644
index 0000000000..23ad566851
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+++ b/media/libvpx/libvpx/vpx_util/vpx_atomics.h
@@ -0,0 +1,111 @@
+/*
+ *  Copyright (c) 2017 The WebM 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.
+ */
+
+#ifndef VPX_VPX_UTIL_VPX_ATOMICS_H_
+#define VPX_VPX_UTIL_VPX_ATOMICS_H_
+
+#include "./vpx_config.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif  // __cplusplus
+
+#if CONFIG_OS_SUPPORT && CONFIG_MULTITHREAD
+
+// Look for built-in atomic support. We cannot use <stdatomic.h> or <atomic>
+// since neither is guaranteed to exist on both C and C++ platforms, and we need
+// to back the atomic type with the same type (g++ needs to be able to use
+// gcc-built code). g++ 6 doesn't support _Atomic as a keyword and can't use the
+// stdatomic.h header. Even if both <stdatomic.h> and <atomic> existed it's not
+// guaranteed that atomic_int is the same type as std::atomic_int.
+// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60932#c13.
+#if !defined(__has_builtin)
+#define __has_builtin(x) 0  // Compatibility with non-clang compilers.
+#endif                      // !defined(__has_builtin)
+
+#if (__has_builtin(__atomic_load_n)) || \
+    (defined(__GNUC__) &&               \
+     (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7)))
+// For GCC >= 4.7 and Clang versions that support __atomic builtins, use those.
+#define VPX_USE_ATOMIC_BUILTINS
+#else
+// Use platform-specific asm barriers.
+#if defined(_MSC_VER)
+// TODO(pbos): This assumes that newer versions of MSVC are building with the
+// default /volatile:ms (or older, where this is always true. Consider adding
+// support for using <atomic> instead of stdatomic.h when building C++11 under
+// MSVC. It's unclear what to do for plain C under /volatile:iso (inline asm?),
+// there're no explicit Interlocked* functions for only storing or loading
+// (presumably because volatile has historically implied that on MSVC).
+//
+// For earlier versions of MSVC or the default /volatile:ms volatile int are
+// acquire/release and require no barrier.
+#define vpx_atomic_memory_barrier() \
+  do {                              \
+  } while (0)
+#else
+#if VPX_ARCH_X86 || VPX_ARCH_X86_64
+// Use a compiler barrier on x86, no runtime penalty.
+#define vpx_atomic_memory_barrier() __asm__ __volatile__("" ::: "memory")
+#elif VPX_ARCH_ARM
+#define vpx_atomic_memory_barrier() __asm__ __volatile__("dmb ish" ::: "memory")
+#elif VPX_ARCH_MIPS
+#define vpx_atomic_memory_barrier() __asm__ __volatile__("sync" ::: "memory")
+#else
+#error Unsupported architecture!
+#endif  // VPX_ARCH_X86 || VPX_ARCH_X86_64
+#endif  // defined(_MSC_VER)
+#endif  // atomic builtin availability check
+
+// These are wrapped in a struct so that they are not easily accessed directly
+// on any platform (to discourage programmer errors by setting values directly).
+// This primitive MUST be initialized using vpx_atomic_init or VPX_ATOMIC_INIT
+// (NOT memset) and accessed through vpx_atomic_ functions.
+typedef struct vpx_atomic_int {
+  volatile int value;
+} vpx_atomic_int;
+
+#define VPX_ATOMIC_INIT(num) \
+  { num }
+
+// Initialization of an atomic int, not thread safe.
+static INLINE void vpx_atomic_init(vpx_atomic_int *atomic, int value) {
+  atomic->value = value;
+}
+
+static INLINE void vpx_atomic_store_release(vpx_atomic_int *atomic, int value) {
+#if defined(VPX_USE_ATOMIC_BUILTINS)
+  __atomic_store_n(&atomic->value, value, __ATOMIC_RELEASE);
+#else
+  vpx_atomic_memory_barrier();
+  atomic->value = value;
+#endif  // defined(VPX_USE_ATOMIC_BUILTINS)
+}
+
+static INLINE int vpx_atomic_load_acquire(const vpx_atomic_int *atomic) {
+#if defined(VPX_USE_ATOMIC_BUILTINS)
+  return __atomic_load_n(&atomic->value, __ATOMIC_ACQUIRE);
+#else
+  int v = atomic->value;
+  vpx_atomic_memory_barrier();
+  return v;
+#endif  // defined(VPX_USE_ATOMIC_BUILTINS)
+}
+
+#undef VPX_USE_ATOMIC_BUILTINS
+#undef vpx_atomic_memory_barrier
+
+#endif /* CONFIG_OS_SUPPORT && CONFIG_MULTITHREAD */
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif  // __cplusplus
+
+#endif  // VPX_VPX_UTIL_VPX_ATOMICS_H_