b4fb99220b
Allow*OnASingleLine appears to no longer apply to typedef structs. Change-Id: If10db1c30c74ee31dad1a0b1926964e850f15fd2
112 lines
4.0 KiB
C++
112 lines
4.0 KiB
C++
/*
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* Copyright (c) 2017 The WebM project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef VPX_UTIL_VPX_ATOMICS_H_
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#define VPX_UTIL_VPX_ATOMICS_H_
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#include "./vpx_config.h"
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#ifdef __cplusplus
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extern "C" {
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#endif // __cplusplus
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#if CONFIG_OS_SUPPORT && CONFIG_MULTITHREAD
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// Look for built-in atomic support. We cannot use <stdatomic.h> or <atomic>
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// since neither is guaranteed to exist on both C and C++ platforms, and we need
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// to back the atomic type with the same type (g++ needs to be able to use
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// gcc-built code). g++ 6 doesn't support _Atomic as a keyword and can't use the
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// stdatomic.h header. Even if both <stdatomic.h> and <atomic> existed it's not
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// guaranteed that atomic_int is the same type as std::atomic_int.
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// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60932#c13.
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#if !defined(__has_builtin)
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#define __has_builtin(x) 0 // Compatibility with non-clang compilers.
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#endif // !defined(__has_builtin)
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#if (__has_builtin(__atomic_load_n)) || \
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(defined(__GNUC__) && \
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(__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7)))
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// For GCC >= 4.7 and Clang versions that support __atomic builtins, use those.
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#define VPX_USE_ATOMIC_BUILTINS
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#else
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// Use platform-specific asm barriers.
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#if defined(_MSC_VER)
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// TODO(pbos): This assumes that newer versions of MSVC are building with the
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// default /volatile:ms (or older, where this is always true. Consider adding
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// support for using <atomic> instead of stdatomic.h when building C++11 under
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// MSVC. It's unclear what to do for plain C under /volatile:iso (inline asm?),
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// there're no explicit Interlocked* functions for only storing or loading
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// (presumably because volatile has historically implied that on MSVC).
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//
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// For earlier versions of MSVC or the default /volatile:ms volatile int are
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// acquire/release and require no barrier.
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#define vpx_atomic_memory_barrier() \
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do { \
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} while (0)
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#else
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#if ARCH_X86 || ARCH_X86_64
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// Use a compiler barrier on x86, no runtime penalty.
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#define vpx_atomic_memory_barrier() __asm__ __volatile__("" ::: "memory")
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#elif ARCH_ARM
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#define vpx_atomic_memory_barrier() __asm__ __volatile__("dmb ish" ::: "memory")
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#elif ARCH_MIPS
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#define vpx_atomic_memory_barrier() __asm__ __volatile__("sync" ::: "memory")
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#else
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#error Unsupported architecture!
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#endif // ARCH_X86 || ARCH_X86_64
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#endif // defined(_MSC_VER)
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#endif // atomic builtin availability check
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// These are wrapped in a struct so that they are not easily accessed directly
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// on any platform (to discourage programmer errors by setting values directly).
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// This primitive MUST be initialized using vpx_atomic_init or VPX_ATOMIC_INIT
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// (NOT memset) and accessed through vpx_atomic_ functions.
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typedef struct vpx_atomic_int {
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volatile int value;
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} vpx_atomic_int;
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#define VPX_ATOMIC_INIT(num) \
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{ num }
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// Initialization of an atomic int, not thread safe.
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static INLINE void vpx_atomic_init(vpx_atomic_int *atomic, int value) {
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atomic->value = value;
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}
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static INLINE void vpx_atomic_store_release(vpx_atomic_int *atomic, int value) {
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#if defined(VPX_USE_ATOMIC_BUILTINS)
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__atomic_store_n(&atomic->value, value, __ATOMIC_RELEASE);
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#else
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vpx_atomic_memory_barrier();
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atomic->value = value;
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#endif // defined(VPX_USE_ATOMIC_BUILTINS)
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}
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static INLINE int vpx_atomic_load_acquire(const vpx_atomic_int *atomic) {
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#if defined(VPX_USE_ATOMIC_BUILTINS)
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return __atomic_load_n(&atomic->value, __ATOMIC_ACQUIRE);
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#else
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int v = atomic->value;
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vpx_atomic_memory_barrier();
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return v;
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#endif // defined(VPX_USE_ATOMIC_BUILTINS)
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}
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#undef VPX_USE_ATOMIC_BUILTINS
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#undef vpx_atomic_memory_barrier
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#endif /* CONFIG_OS_SUPPORT && CONFIG_MULTITHREAD */
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#ifdef __cplusplus
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} // extern "C"
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#endif // __cplusplus
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#endif // VPX_UTIL_VPX_ATOMICS_H_
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