103 lines
2.0 KiB
C
103 lines
2.0 KiB
C
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// The LazyInstance<Type> class manages a single instance of Type,
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// which will be lazily created on the first time it's accessed
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#ifndef BASE_MEMORY_LAZY_INSTANCE_H_
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#define BASE_MEMORY_LAZY_INSTANCE_H_
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#include "base/base_config.h"
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#include "base/third_party/chrome/atomicops.h"
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#include "base/thread/thread.h"
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#include "base/util/at_exit.h"
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//#include "base/log/log.h"
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namespace nbase
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{
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template<typename Type>
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class LazyInstance
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{
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public:
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LazyInstance() : instance_(NULL)
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{
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base::subtle::NoBarrier_Store(&state_, kNone);
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}
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~LazyInstance()
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{
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// |instance_| should be deleted by |OnExit|
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//DCHECK(instance_ == 0);
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}
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Type& Get()
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{
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return *Pointer();
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}
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Type* Pointer()
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{
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using namespace base::subtle;
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if (Acquire_Load(&state_) != kCreated)
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{
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Atomic32 state =
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NoBarrier_CompareAndSwap(&state_, kNone, kCreating);
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if (state == kNone)
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{
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// we take the chance to create the instance
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instance_ = reinterpret_cast<AtomicWord>(new Type());
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AtExitManager::RegisterCallback(OnExit, this);
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Release_Store(&state_, kCreated);
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}
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else if (state != kCreated)
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{
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// wait, util another thread created the instance
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while (Acquire_Load(&state_) != kCreated)
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Thread::YieldThread();
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}
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}
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return reinterpret_cast<Type *>(instance_);
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}
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bool operator ==(Type *object) const
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{
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switch (base::subtle::NoBarrier_Load(&state_))
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{
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case kNone:
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return object == NULL;
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case kCreating:
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case kCreated:
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return instance_ == object;
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default:
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return false;
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}
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}
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private:
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enum
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{
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kNone = 0,
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kCreating,
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kCreated,
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kDeleting,
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};
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static void OnExit(void *lazy_instance)
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{
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LazyInstance<Type>* me =
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reinterpret_cast<LazyInstance<Type>*>(lazy_instance);
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delete reinterpret_cast<Type*>(me->instance_);
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base::subtle::NoBarrier_Store(&me->instance_, 0);
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}
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base::subtle::Atomic32 state_;
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base::subtle::AtomicWord instance_;
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DISALLOW_COPY_AND_ASSIGN(LazyInstance);
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};
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}
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#endif // BASE_MEMORY_LAZY_INSTANCE_H_
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