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1 /* | 1 /* |
2 * Copyright (C) 2013 Google Inc. All rights reserved. | 2 * Copyright (C) 2013 Google Inc. All rights reserved. |
3 * | 3 * |
4 * Redistribution and use in source and binary forms, with or without | 4 * Redistribution and use in source and binary forms, with or without |
5 * modification, are permitted provided that the following conditions are | 5 * modification, are permitted provided that the following conditions are |
6 * met: | 6 * met: |
7 * | 7 * |
8 * * Redistributions of source code must retain the above copyright | 8 * * Redistributions of source code must retain the above copyright |
9 * notice, this list of conditions and the following disclaimer. | 9 * notice, this list of conditions and the following disclaimer. |
10 * * Redistributions in binary form must reproduce the above | 10 * * Redistributions in binary form must reproduce the above |
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24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | 24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | 25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | 26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | 27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | 28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
29 */ | 29 */ |
30 | 30 |
31 #ifndef WTF_SpinLock_h | 31 #ifndef WTF_SpinLock_h |
32 #define WTF_SpinLock_h | 32 #define WTF_SpinLock_h |
33 | 33 |
| 34 #include "wtf/Compiler.h" |
| 35 #include "wtf/WTFExport.h" |
| 36 #include <atomic> |
| 37 #include <memory> |
| 38 #include <mutex> |
| 39 |
34 // DESCRIPTION | 40 // DESCRIPTION |
35 // spinLockLock() and spinLockUnlock() are simple spinlock primitives based on | 41 // Spinlock is a simple spinlock class based on the standard CPU primitive of |
36 // the standard CPU primitive of atomic increment and decrement of an int at | 42 // atomic increment and decrement of an int at a given memory address. These are |
37 // a given memory address. These are intended only for very short duration locks | 43 // intended only for very short duration locks and assume a system with multiple |
38 // and assume a system with multiple cores. For any potentially longer wait you | 44 // cores. For any potentially longer wait you should be using a real lock. |
39 // should be using a real lock. | |
40 | |
41 #include "wtf/Atomics.h" | |
42 | 45 |
43 namespace WTF { | 46 namespace WTF { |
44 | 47 |
45 // This is called if the initial attempt to acquire the lock fails. It's a bit | 48 class SpinLock { |
46 // slower, but has a much better scheduling and power consumption behavior. | 49 public: |
47 WTF_EXPORT void slowSpinLockLock(int volatile* lock); | 50 using Guard = std::lock_guard<SpinLock>; |
48 | 51 |
49 ALWAYS_INLINE void spinLockLock(int volatile* lock) | 52 ALWAYS_INLINE void lock() |
50 { | 53 { |
51 if (LIKELY(!atomicTestAndSetToOne(lock))) | 54 static_assert(sizeof(m_lock) == sizeof(int), "int and m_lock are differe
nt sizes"); |
52 return; | 55 if (LIKELY(!m_lock.exchange(true, std::memory_order_acq_rel))) |
53 slowSpinLockLock(lock); | 56 return; |
54 } | 57 lockSlow(); |
| 58 } |
55 | 59 |
56 ALWAYS_INLINE void spinLockUnlock(int volatile* lock) | 60 ALWAYS_INLINE void unlock() |
57 { | 61 { |
58 atomicSetOneToZero(lock); | 62 m_lock.store(false, std::memory_order_release); |
59 } | 63 } |
| 64 |
| 65 private: |
| 66 // This is called if the initial attempt to acquire the lock fails. It's |
| 67 // slower, but has a much better scheduling and power consumption behavior. |
| 68 WTF_EXPORT void lockSlow(); |
| 69 |
| 70 std::atomic<int> m_lock; |
| 71 }; |
| 72 |
60 | 73 |
61 } // namespace WTF | 74 } // namespace WTF |
62 | 75 |
63 using WTF::spinLockLock; | 76 using WTF::SpinLock; |
64 using WTF::spinLockUnlock; | |
65 | 77 |
66 #endif // WTF_SpinLock_h | 78 #endif // WTF_SpinLock_h |
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