From 79e548eb98caefd3ea0f0e4806a7abca6654e7dc Mon Sep 17 00:00:00 2001 From: Chris Palmer Date: Thu, 16 Mar 2017 11:39:48 -0700 Subject: Import PartitionAlloc from Chromium. We'll add callers in a later CL. BUG=pdfium:678 Change-Id: I98c8b2832c4750df326218e24ee8c1bd33b89b50 Reviewed-on: https://pdfium-review.googlesource.com/3066 Commit-Queue: Tom Sepez Reviewed-by: Tom Sepez --- .../allocator/partition_allocator/spin_lock.cc | 84 ++++++++++++++++++++++ 1 file changed, 84 insertions(+) create mode 100644 third_party/base/allocator/partition_allocator/spin_lock.cc (limited to 'third_party/base/allocator/partition_allocator/spin_lock.cc') diff --git a/third_party/base/allocator/partition_allocator/spin_lock.cc b/third_party/base/allocator/partition_allocator/spin_lock.cc new file mode 100644 index 0000000000..803e4d6abc --- /dev/null +++ b/third_party/base/allocator/partition_allocator/spin_lock.cc @@ -0,0 +1,84 @@ +// Copyright 2015 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#include "third_party/base/allocator/partition_allocator/spin_lock.h" + +#if defined(OS_WIN) +#include +#elif defined(OS_POSIX) +#include +#endif + +// The YIELD_PROCESSOR macro wraps an architecture specific-instruction that +// informs the processor we're in a busy wait, so it can handle the branch more +// intelligently and e.g. reduce power to our core or give more resources to the +// other hyper-thread on this core. See the following for context: +// https://software.intel.com/en-us/articles/benefitting-power-and-performance-sleep-loops +// +// The YIELD_THREAD macro tells the OS to relinquish our quantum. This is +// basically a worst-case fallback, and if you're hitting it with any frequency +// you really should be using a proper lock (such as |base::Lock|)rather than +// these spinlocks. +#if defined(OS_WIN) +#define YIELD_PROCESSOR YieldProcessor() +#define YIELD_THREAD SwitchToThread() +#elif defined(COMPILER_GCC) || defined(__clang__) +#if defined(ARCH_CPU_X86_64) || defined(ARCH_CPU_X86) +#define YIELD_PROCESSOR __asm__ __volatile__("pause") +#elif defined(ARCH_CPU_ARMEL) || defined(ARCH_CPU_ARM64) +#define YIELD_PROCESSOR __asm__ __volatile__("yield") +#elif defined(ARCH_CPU_MIPSEL) +// The MIPS32 docs state that the PAUSE instruction is a no-op on older +// architectures (first added in MIPS32r2). To avoid assembler errors when +// targeting pre-r2, we must encode the instruction manually. +#define YIELD_PROCESSOR __asm__ __volatile__(".word 0x00000140") +#elif defined(ARCH_CPU_MIPS64EL) && __mips_isa_rev >= 2 +// Don't bother doing using .word here since r2 is the lowest supported mips64 +// that Chromium supports. +#define YIELD_PROCESSOR __asm__ __volatile__("pause") +#endif +#endif + +#ifndef YIELD_PROCESSOR +#warning "Processor yield not supported on this architecture." +#define YIELD_PROCESSOR ((void)0) +#endif + +#ifndef YIELD_THREAD +#if defined(OS_POSIX) +#define YIELD_THREAD sched_yield() +#else +#warning "Thread yield not supported on this OS." +#define YIELD_THREAD ((void)0) +#endif +#endif + +namespace pdfium { +namespace base { +namespace subtle { + +void SpinLock::LockSlow() { + // The value of |kYieldProcessorTries| is cargo culted from TCMalloc, Windows + // critical section defaults, and various other recommendations. + // TODO(jschuh): Further tuning may be warranted. + static const int kYieldProcessorTries = 1000; + do { + do { + for (int count = 0; count < kYieldProcessorTries; ++count) { + // Let the processor know we're spinning. + YIELD_PROCESSOR; + if (!lock_.load(std::memory_order_relaxed) && + LIKELY(!lock_.exchange(true, std::memory_order_acquire))) + return; + } + + // Give the OS a chance to schedule something on this core. + YIELD_THREAD; + } while (lock_.load(std::memory_order_relaxed)); + } while (UNLIKELY(lock_.exchange(true, std::memory_order_acquire))); +} + +} // namespace subtle +} // namespace base +} // namespace pdfium -- cgit v1.2.3