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Side by Side Diff: third_party/WebKit/Source/wtf/SpinLock.cpp

Issue 2484803003: Move WTF::SpinLock to base::SpinLock. (Closed)
Patch Set: base::SpinLock → base::subtle::SpinLock, plus a warning comment. Created 4 years, 1 month ago
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1 // Copyright 2015 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "wtf/SpinLock.h"
6
7 #include "wtf/Atomics.h"
8 #include "wtf/CPU.h"
9 #include "wtf/Compiler.h"
10
11 #if OS(WIN)
12 #include <windows.h>
13 #elif OS(POSIX)
14 #include <sched.h>
15 #endif
16
17 // The YIELD_PROCESSOR macro wraps an architecture specific-instruction that
18 // informs the processor we're in a busy wait, so it can handle the branch more
19 // intelligently and e.g. reduce power to our core or give more resources to the
20 // other hyper-thread on this core. See the following for context:
21 // https://software.intel.com/en-us/articles/benefitting-power-and-performance-s leep-loops
22 //
23 // The YIELD_THREAD macro tells the OS to relinquish our quanta. This is
24 // basically a worst-case fallback, and if you're hitting it with any frequency
25 // you really should be using proper lock rather than these spinlocks.
26 #if OS(WIN)
27 #define YIELD_PROCESSOR YieldProcessor()
28 #define YIELD_THREAD SwitchToThread()
29 #elif COMPILER(GCC) || COMPILER(CLANG)
30 #if CPU(X86_64) || CPU(X86)
31 #define YIELD_PROCESSOR __asm__ __volatile__("pause")
32 #elif CPU(ARM) || CPU(ARM64)
33 #define YIELD_PROCESSOR __asm__ __volatile__("yield")
34 #elif CPU(MIPS)
35 // The MIPS32 docs state that the PAUSE instruction is a no-op on older
36 // architectures (first added in MIPS32r2). To avoid assembler errors when
37 // targeting pre-r2, we must encode the instruction manually.
38 #define YIELD_PROCESSOR __asm__ __volatile__(".word 0x00000140")
39 #elif CPU(MIPS64) && __mips_isa_rev >= 2
40 // Don't bother doing using .word here since r2 is the lowest supported mips64
41 // that Chromium supports.
42 #define YIELD_PROCESSOR __asm__ __volatile__("pause")
43 #endif
44 #endif
45
46 #ifndef YIELD_PROCESSOR
47 #warning "Processor yield not supported on this architecture."
48 #define YIELD_PROCESSOR ((void)0)
49 #endif
50
51 #ifndef YIELD_THREAD
52 #if OS(POSIX)
53 #define YIELD_THREAD sched_yield()
54 #else
55 #warning "Thread yield not supported on this OS."
56 #define YIELD_THREAD ((void)0)
57 #endif
58 #endif
59
60 namespace WTF {
61
62 void SpinLock::lockSlow() {
63 // The value of kYieldProcessorTries is cargo culted from TCMalloc, Windows
64 // critical section defaults, and various other recommendations.
65 // TODO(jschuh): Further tuning may be warranted.
66 static const int kYieldProcessorTries = 1000;
67 do {
68 do {
69 for (int count = 0; count < kYieldProcessorTries; ++count) {
70 // Let the Processor know we're spinning.
71 YIELD_PROCESSOR;
72 if (!m_lock.load(std::memory_order_relaxed) &&
73 LIKELY(!m_lock.exchange(true, std::memory_order_acquire)))
74 return;
75 }
76
77 // Give the OS a chance to schedule something on this core.
78 YIELD_THREAD;
79 } while (m_lock.load(std::memory_order_relaxed));
80 } while (UNLIKELY(m_lock.exchange(true, std::memory_order_acquire)));
81 }
82
83 } // namespace WTF
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