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| 1 // Copyright 2015 The Chromium Authors. All rights reserved. | 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 | 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
| 4 | 4 |
| 5 #include "config.h" | 5 #include "config.h" |
| 6 #include "wtf/SpinLock.h" | 6 #include "wtf/SpinLock.h" |
| 7 | 7 |
| 8 #include "wtf/Atomics.h" | 8 #include "wtf/Atomics.h" |
| 9 #include "wtf/CPU.h" | 9 #include "wtf/CPU.h" |
| 10 #include "wtf/Compiler.h" | 10 #include "wtf/Compiler.h" |
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| 44 #if OS(POSIX) | 44 #if OS(POSIX) |
| 45 #define YIELD_THREAD sched_yield() | 45 #define YIELD_THREAD sched_yield() |
| 46 #else | 46 #else |
| 47 #warning "Thread yield not supported on this OS." | 47 #warning "Thread yield not supported on this OS." |
| 48 #define YIELD_THREAD ((void)0) | 48 #define YIELD_THREAD ((void)0) |
| 49 #endif | 49 #endif |
| 50 #endif | 50 #endif |
| 51 | 51 |
| 52 namespace WTF { | 52 namespace WTF { |
| 53 | 53 |
| 54 void slowSpinLockLock(int volatile* lock) | 54 void slowSpinLockLock(int volatile* lock) { |
| 55 { | 55 // The value of kYieldProcessorTries is cargo culted from TCMalloc, Windows |
| 56 // The value of kYieldProcessorTries is cargo culted from TCMalloc, Windows | 56 // critical section defaults, and various other recommendations. |
| 57 // critical section defaults, and various other recommendations. | 57 // TODO(jschuh): Further tuning may be warranted. |
| 58 // TODO(jschuh): Further tuning may be warranted. | 58 static const int kYieldProcessorTries = 1000; |
| 59 static const int kYieldProcessorTries = 1000; | 59 do { |
| 60 do { | 60 do { |
| 61 do { | 61 for (int count = 0; count < kYieldProcessorTries; ++count) { |
| 62 for (int count = 0; count < kYieldProcessorTries; ++count) { | 62 // Let the Processor know we're spinning. |
| 63 // Let the Processor know we're spinning. | 63 YIELD_PROCESSOR; |
| 64 YIELD_PROCESSOR; | 64 if (!*lock && LIKELY(!atomicTestAndSetToOne(lock))) |
| 65 if (!*lock && LIKELY(!atomicTestAndSetToOne(lock))) | 65 return; |
| 66 return; | 66 } |
| 67 } | |
| 68 | 67 |
| 69 // Give the OS a chance to schedule something on this core. | 68 // Give the OS a chance to schedule something on this core. |
| 70 YIELD_THREAD; | 69 YIELD_THREAD; |
| 71 } while (*lock); | 70 } while (*lock); |
| 72 } while (UNLIKELY(atomicTestAndSetToOne(lock))); | 71 } while (UNLIKELY(atomicTestAndSetToOne(lock))); |
| 73 } | 72 } |
| 74 | 73 |
| 75 } // namespace WTF | 74 } // namespace WTF |
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