From a669bc7a7ae7580c5cd92067aeb95d09e64ea720 Mon Sep 17 00:00:00 2001 From: mtklein Date: Mon, 2 Feb 2015 12:22:07 -0800 Subject: Atomics overhaul. This merges and refactors SkAtomics.h and SkBarriers.h into SkAtomics.h and some ports/ implementations. The major new feature is that we can express memory orders explicitly rather than only through comments. The porting layer is reduced to four template functions: - sk_atomic_load - sk_atomic_store - sk_atomic_fetch_add - sk_atomic_compare_exchange From those four we can reconstruct all our previous sk_atomic_foo. There are three ports: - SkAtomics_std: uses C++11 , used with MSVC - SkAtomics_atomic: uses newer GCC/Clang intrinsics, used on not-MSVC where possible - SkAtomics_sync: uses older GCC/Clang intrinsics, used where SkAtomics_atomic not supported No public API changes. TBR=reed@google.com BUG=skia: Review URL: https://codereview.chromium.org/896553002 --- include/ports/SkAtomics_sync.h | 78 ++++++++++++++++++++---------------------- 1 file changed, 37 insertions(+), 41 deletions(-) (limited to 'include/ports/SkAtomics_sync.h') diff --git a/include/ports/SkAtomics_sync.h b/include/ports/SkAtomics_sync.h index 9389c00103..66da4d35ee 100644 --- a/include/ports/SkAtomics_sync.h +++ b/include/ports/SkAtomics_sync.h @@ -1,55 +1,51 @@ -/* - * Copyright 2013 Google Inc. - * - * Use of this source code is governed by a BSD-style license that can be - * found in the LICENSE file. - */ - #ifndef SkAtomics_sync_DEFINED #define SkAtomics_sync_DEFINED -/** GCC/Clang __sync based atomics. */ - -#include - -static inline __attribute__((always_inline)) int32_t sk_atomic_inc(int32_t* addr) { - return __sync_fetch_and_add(addr, 1); +// This file is mostly a shim. We'd like to delete it. Please don't put much +// effort into maintaining it, and if you find bugs in it, the right fix is to +// delete this file and upgrade your compiler to something that supports +// __atomic builtins or std::atomic. + +static inline void barrier(sk_memory_order mo) { + asm volatile("" : : : "memory"); // Prevents the compiler from reordering code. + #if SK_CPU_X86 + // On x86, we generally don't need an extra memory barrier for loads or stores. + if (sk_memory_order_seq_cst == mo) { __sync_synchronize(); } + #else + // On other platforms (e.g. ARM) we do unless the memory order is relaxed. + if (sk_memory_order_relaxed != mo) { __sync_synchronize(); } + #endif } -static inline __attribute__((always_inline)) int64_t sk_atomic_inc(int64_t* addr) { -#if defined(__mips__) && !defined(__LP64__) && !defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8) - /** Some versions of the GCC 32-bit MIPS toolchains (e.g. 4.8) for android are missing - * support for the __sync* functions that operate on 64-bit values. The workaround - * is to use __atomic* functions until we can move everything to . - */ - return __atomic_fetch_add(addr, 1, __ATOMIC_SEQ_CST); -#else - return __sync_fetch_and_add(addr, 1); -#endif -} +// These barriers only support our majority use cases: acquire and relaxed loads, release stores. +// For anything more complicated, please consider deleting this file and upgrading your compiler. -static inline __attribute__((always_inline)) int32_t sk_atomic_add(int32_t* addr, int32_t inc) { - return __sync_fetch_and_add(addr, inc); +template +T sk_atomic_load(const T* ptr, sk_memory_order mo) { + T val = *ptr; + barrier(mo); + return val; } -static inline __attribute__((always_inline)) int32_t sk_atomic_dec(int32_t* addr) { - return __sync_fetch_and_add(addr, -1); +template +void sk_atomic_store(T* ptr, T val, sk_memory_order mo) { + barrier(mo); + *ptr = val; } -static inline __attribute__((always_inline)) void sk_membar_acquire__after_atomic_dec() { } - -static inline __attribute__((always_inline)) bool sk_atomic_cas(int32_t* addr, - int32_t before, - int32_t after) { - return __sync_bool_compare_and_swap(addr, before, after); +template +T sk_atomic_fetch_add(T* ptr, T val, sk_memory_order) { + return __sync_fetch_and_add(ptr, val); } -static inline __attribute__((always_inline)) void* sk_atomic_cas(void** addr, - void* before, - void* after) { - return __sync_val_compare_and_swap(addr, before, after); +template +bool sk_atomic_compare_exchange(T* ptr, T* expected, T desired, sk_memory_order, sk_memory_order) { + T prev = __sync_val_compare_and_swap(ptr, *expected, desired); + if (prev == *expected) { + return true; + } + *expected = prev; + return false; } -static inline __attribute__((always_inline)) void sk_membar_acquire__after_atomic_conditional_inc() { } - -#endif +#endif//SkAtomics_sync_DEFINED -- cgit v1.2.3