identity.h

//
// Copyright 2016 Pixar
//
// Licensed under the Apache License, Version 2.0 (the "Apache License")
// with the following modification; you may not use this file except in
// compliance with the Apache License and the following modification to it:
// Section 6. Trademarks. is deleted and replaced with:
//
// 6. Trademarks. This License does not grant permission to use the trade
//    names, trademarks, service marks, or product names of the Licensor
//    and its affiliates, except as required to comply with Section 4(c) of
//    the License and to reproduce the content of the NOTICE file.
//
// You may obtain a copy of the Apache License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Apache License with the above modification is
// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the Apache License for the specific
// language governing permissions and limitations under the Apache License.
//
#ifndef PXR_USD_SDF_IDENTITY_H
#define PXR_USD_SDF_IDENTITY_H
 
#include "pxr/pxr.h"
#include "pxr/usd/sdf/api.h"
#include "pxr/usd/sdf/declareHandles.h"
#include "pxr/usd/sdf/path.h"
 
#include <memory>
 
PXR_NAMESPACE_OPEN_SCOPE
 
class Sdf_IdentityRegistry;
class Sdf_IdRegistryImpl;
 
SDF_DECLARE_HANDLES(SdfLayer);
 
class Sdf_Identity {
    Sdf_Identity(Sdf_Identity const &) = delete;
    Sdf_Identity &operator=(Sdf_Identity const &) = delete;
public:
    SDF_API
    const SdfLayerHandle &GetLayer() const;
 
    const SdfPath &GetPath() const {
        return _path;
    }
    
private:
    // Ref-counting ops manage _refCount.
    friend void TfDelegatedCountIncrement(Sdf_Identity*);
    friend void TfDelegatedCountDecrement(Sdf_Identity*) noexcept;
 
    friend class Sdf_IdentityRegistry;
    friend class Sdf_IdRegistryImpl;
 
    Sdf_Identity(Sdf_IdRegistryImpl *regImpl, const SdfPath &path)
        : _refCount(0), _path(path), _regImpl(regImpl) {}
    
    SDF_API
    static void _UnregisterOrDelete(Sdf_IdRegistryImpl *reg, Sdf_Identity *id)
    noexcept;
    void _Forget();
 
    mutable std::atomic_int _refCount;
    SdfPath _path;
    Sdf_IdRegistryImpl *_regImpl;
};
 
// Specialize TfDelegatedCountPtr operations.
inline void TfDelegatedCountIncrement(PXR_NS::Sdf_Identity* p) {
    ++p->_refCount;
}
inline void TfDelegatedCountDecrement(PXR_NS::Sdf_Identity* p) noexcept {
    // Once the count hits zero, p is liable to be destroyed at any point,
    // concurrently, by its owning registry if it happens to be doing a cleanup
    // pass.  Cache 'this' and the impl ptr in local variables so we have them
    // before decrementing the count.
    Sdf_Identity *self = p;
    Sdf_IdRegistryImpl *reg = p->_regImpl;
    if (--p->_refCount == 0) {
        // Cannot use 'p' anymore here.
        Sdf_Identity::_UnregisterOrDelete(reg, self);
    }
}
 
class Sdf_IdentityRegistry {
    Sdf_IdentityRegistry(const Sdf_IdentityRegistry&) = delete;
    Sdf_IdentityRegistry& operator=(const Sdf_IdentityRegistry&) = delete;
public:
    Sdf_IdentityRegistry(const SdfLayerHandle &layer);
    ~Sdf_IdentityRegistry();
 
    const SdfLayerHandle &GetLayer() const {
        return _layer;
    }
 
    Sdf_IdentityRefPtr Identify(const SdfPath &path);
 
    void MoveIdentity(const SdfPath &oldPath, const SdfPath &newPath);
    
private:
    friend class Sdf_Identity;
 
    friend class Sdf_IdRegistryImpl;
 
    // Remove the identity mapping for \a path to \a id from the registry.  This
    // is invoked when an identity's refcount hits zero.
    SDF_API
    void _UnregisterOrDelete();
 
    const SdfLayerHandle _layer;
 
    // Private implementation.
    const std::unique_ptr<Sdf_IdRegistryImpl> _impl;
};
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_USD_SDF_IDENTITY_H