// Copyright 2008 Google Inc.

// All rights reserved.

// Atomic increment and decrement for reference counting.

// For atomic operations on statistics counters and sequence numbers,

// see atomic_stats_counter.h and atomic_sequence_num.h respectively.

// Some clients use atomic operations for reference counting.

// you use one of them:

//         util/refcount/reference_counted.h

//         util/gtl/refcounted_ptr.h

//         util/gtl/shared_ptr.h

// Alternatively, use a Mutex to maintain your reference count.

// If you really must build your own reference counts with atomic operations,

// use the following routines in the way suggested by this example:

//    AtomicWord ref_count_;  // remember to initialize this to 0

//    ...

//    void Ref() {

//      base::RefCountInc(&this->ref_count_);

//    }

//    void Unref() {

//      if (!base::RefCountDec(&this->ref_count_)) {

//        delete this;

//      }

//    }

// Using these routines (rather than the ones in atomicops.h) will provide the

// correct semantics; in particular, the memory ordering needed to make

// reference counting work will be guaranteed.

// You need not declare the reference count word "volatile".  After

// initialization you should use the word only via the routines below; the

// "volatile" in the signatures below is for backwards compatibility.

//

// If you need to do something very different from this, use a Mutex.

#pragma once

#include <glog/logging.h>

#include "gutil/atomicops.h"

namespace base {

// These calls are available for both Atomic32, and AtomicWord types,

// and also for base::subtle::Atomic64 if available on the platform.

// Normally, clients are expected to use RefCountInc/RefCountDec.

// In rare cases, it may be necessary to adjust the reference count by

// more than 1, in which case they may use RefCountIncN/RefCountDecN.

// Increment a reference count by "increment", which must exceed 0.

inline void RefCountIncN(volatile Atomic32* ptr, Atomic32 increment) {

    DCHECK_GT(increment, 0);

    base::subtle::NoBarrier_AtomicIncrement(ptr, increment);

}

// Decrement a reference count by "decrement", which must exceed 0,

// and return whether the result is non-zero.

// Insert barriers to ensure that state written before the reference count

// became zero will be visible to a thread that has just made the count zero.

inline bool RefCountDecN(volatile Atomic32* ptr, Atomic32 decrement) {

    DCHECK_GT(decrement, 0);

    bool res = base::subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0;

    return res;

}

// Increment a reference count by 1.

inline void RefCountInc(volatile Atomic32* ptr) {

    base::RefCountIncN(ptr, 1);

}

// Decrement a reference count by 1 and return whether the result is non-zero.

// Insert barriers to ensure that state written before the reference count

// became zero will be visible to a thread that has just made the count zero.

inline bool RefCountDec(volatile Atomic32* ptr) {

    return base::RefCountDecN(ptr, 1);

}

// Return whether the reference count is one.

// If the reference count is used in the conventional way, a

// reference count of 1 implies that the current thread owns the

// reference and no other thread shares it.

// This call performs the test for a reference count of one, and

// performs the memory barrier needed for the owning thread

// to act on the object, knowing that it has exclusive access to the

// object.

inline bool RefCountIsOne(const volatile Atomic32* ptr) {

    return base::subtle::Acquire_Load(ptr) == 1;

}

// Return whether the reference count is zero.  With conventional object

// referencing counting, the object will be destroyed, so the reference count

// should never be zero.  Hence this is generally used for a debug check.

inline bool RefCountIsZero(const volatile Atomic32* ptr) {

    return subtle::Acquire_Load(ptr) == 0;

}

#if BASE_HAS_ATOMIC64

// Implementations for Atomic64, if available.

inline void RefCountIncN(volatile base::subtle::Atomic64* ptr, base::subtle::Atomic64 increment) {

    DCHECK_GT(increment, 0);

    base::subtle::NoBarrier_AtomicIncrement(ptr, increment);

}

inline bool RefCountDecN(volatile base::subtle::Atomic64* ptr, base::subtle::Atomic64 decrement) {

    DCHECK_GT(decrement, 0);

    return base::subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0;

}

inline void RefCountInc(volatile base::subtle::Atomic64* ptr) {

    base::RefCountIncN(ptr, 1);

}

inline bool RefCountDec(volatile base::subtle::Atomic64* ptr) {

    return base::RefCountDecN(ptr, 1);

}

inline bool RefCountIsOne(const volatile base::subtle::Atomic64* ptr) {

    return base::subtle::Acquire_Load(ptr) == 1;

}

inline bool RefCountIsZero(const volatile base::subtle::Atomic64* ptr) {

    return base::subtle::Acquire_Load(ptr) == 0;

}

#endif

#ifdef AtomicWordCastType

// Implementations for AtomicWord, if it's a different type from the above.

inline void RefCountIncN(volatile AtomicWord* ptr, AtomicWord increment) {

    base::RefCountIncN(reinterpret_cast<volatile AtomicWordCastType*>(ptr), increment);

}

inline bool RefCountDecN(volatile AtomicWord* ptr, AtomicWord decrement) {

    return base::RefCountDecN(reinterpret_cast<volatile AtomicWordCastType*>(ptr), decrement);

}

inline void RefCountInc(volatile AtomicWord* ptr) {

    base::RefCountIncN(ptr, 1);

}

inline bool RefCountDec(volatile AtomicWord* ptr) {

    return base::RefCountDecN(ptr, 1);

}

inline bool RefCountIsOne(const volatile AtomicWord* ptr) {

    return base::subtle::Acquire_Load(reinterpret_cast<const volatile AtomicWordCastType*>(ptr)) ==

           1;

}

inline bool RefCountIsZero(const volatile AtomicWord* ptr) {

    return base::subtle::Acquire_Load(reinterpret_cast<const volatile AtomicWordCastType*>(ptr)) ==

           0;

}

#endif

} // namespace base