| /* Copyright (c) 2006, Google Inc. |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are |
| * met: |
| * |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * Redistributions in binary form must reproduce the above |
| * copyright notice, this list of conditions and the following disclaimer |
| * in the documentation and/or other materials provided with the |
| * distribution. |
| * * Neither the name of Google Inc. nor the names of its |
| * contributors may be used to endorse or promote products derived from |
| * this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| * |
| * --- |
| * Author: Sanjay Ghemawat |
| */ |
| |
| // SpinLock is async signal safe. |
| // If used within a signal handler, all lock holders |
| // should block the signal even outside the signal handler. |
| |
| #ifndef BASE_SPINLOCK_H_ |
| #define BASE_SPINLOCK_H_ |
| |
| #include <config.h> |
| #include "base/atomicops.h" |
| #include "base/basictypes.h" |
| #include "base/dynamic_annotations.h" |
| #include "base/thread_annotations.h" |
| |
| class LOCKABLE SpinLock { |
| public: |
| SpinLock() : lockword_(kSpinLockFree) { } |
| |
| // Special constructor for use with static SpinLock objects. E.g., |
| // |
| // static SpinLock lock(base::LINKER_INITIALIZED); |
| // |
| // When intialized using this constructor, we depend on the fact |
| // that the linker has already initialized the memory appropriately. |
| // A SpinLock constructed like this can be freely used from global |
| // initializers without worrying about the order in which global |
| // initializers run. |
| explicit SpinLock(base::LinkerInitialized /*x*/) { |
| // Does nothing; lockword_ is already initialized |
| } |
| |
| // Acquire this SpinLock. |
| // TODO(csilvers): uncomment the annotation when we figure out how to |
| // support this macro with 0 args (see thread_annotations.h) |
| inline void Lock() /*EXCLUSIVE_LOCK_FUNCTION()*/ { |
| if (base::subtle::Acquire_CompareAndSwap(&lockword_, kSpinLockFree, |
| kSpinLockHeld) != kSpinLockFree) { |
| SlowLock(); |
| } |
| ANNOTATE_RWLOCK_ACQUIRED(this, 1); |
| } |
| |
| // Try to acquire this SpinLock without blocking and return true if the |
| // acquisition was successful. If the lock was not acquired, false is |
| // returned. If this SpinLock is free at the time of the call, TryLock |
| // will return true with high probability. |
| inline bool TryLock() EXCLUSIVE_TRYLOCK_FUNCTION(true) { |
| bool res = |
| (base::subtle::Acquire_CompareAndSwap(&lockword_, kSpinLockFree, |
| kSpinLockHeld) == kSpinLockFree); |
| if (res) { |
| ANNOTATE_RWLOCK_ACQUIRED(this, 1); |
| } |
| return res; |
| } |
| |
| // Release this SpinLock, which must be held by the calling thread. |
| // TODO(csilvers): uncomment the annotation when we figure out how to |
| // support this macro with 0 args (see thread_annotations.h) |
| inline void Unlock() /*UNLOCK_FUNCTION()*/ { |
| ANNOTATE_RWLOCK_RELEASED(this, 1); |
| uint64 wait_cycles = static_cast<uint64>( |
| base::subtle::Release_AtomicExchange(&lockword_, kSpinLockFree)); |
| if (wait_cycles != kSpinLockHeld) { |
| // Collect contentionz profile info, and speed the wakeup of any waiter. |
| // The wait_cycles value indicates how long this thread spent waiting |
| // for the lock. |
| SlowUnlock(wait_cycles); |
| } |
| } |
| |
| // Determine if the lock is held. When the lock is held by the invoking |
| // thread, true will always be returned. Intended to be used as |
| // CHECK(lock.IsHeld()). |
| inline bool IsHeld() const { |
| return base::subtle::NoBarrier_Load(&lockword_) != kSpinLockFree; |
| } |
| |
| static const base::LinkerInitialized LINKER_INITIALIZED; // backwards compat |
| private: |
| enum { kSpinLockFree = 0 }; |
| enum { kSpinLockHeld = 1 }; |
| enum { kSpinLockSleeper = 2 }; |
| |
| volatile Atomic32 lockword_; |
| |
| void SlowLock(); |
| void SlowUnlock(uint64 wait_cycles); |
| Atomic32 SpinLoop(int64 initial_wait_timestamp, Atomic32* wait_cycles); |
| inline int32 CalculateWaitCycles(int64 wait_start_time); |
| |
| DISALLOW_COPY_AND_ASSIGN(SpinLock); |
| }; |
| |
| // Corresponding locker object that arranges to acquire a spinlock for |
| // the duration of a C++ scope. |
| class SCOPED_LOCKABLE SpinLockHolder { |
| private: |
| SpinLock* lock_; |
| public: |
| inline explicit SpinLockHolder(SpinLock* l) EXCLUSIVE_LOCK_FUNCTION(l) |
| : lock_(l) { |
| l->Lock(); |
| } |
| // TODO(csilvers): uncomment the annotation when we figure out how to |
| // support this macro with 0 args (see thread_annotations.h) |
| inline ~SpinLockHolder() /*UNLOCK_FUNCTION()*/ { lock_->Unlock(); } |
| }; |
| // Catch bug where variable name is omitted, e.g. SpinLockHolder (&lock); |
| #define SpinLockHolder(x) COMPILE_ASSERT(0, spin_lock_decl_missing_var_name) |
| |
| |
| #endif // BASE_SPINLOCK_H_ |