src/dawn/wire/server/ObjectStorage.h

// Copyright 2019 The Dawn & Tint Authors
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.
//
// 2. 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.
//
// 3. Neither the name of the copyright holder 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"
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#ifndef SRC_DAWN_WIRE_SERVER_OBJECTSTORAGE_H_
#define SRC_DAWN_WIRE_SERVER_OBJECTSTORAGE_H_

#include <algorithm>
#include <map>
#include <memory>
#include <utility>
#include <vector>

#include "absl/container/flat_hash_set.h"
#include "dawn/wire/WireCmd_autogen.h"
#include "dawn/wire/WireServer.h"
#include "partition_alloc/pointers/raw_ptr.h"

namespace dawn::wire::server {

// Whether this object has been allocated, or reserved for async object creation.
// Used by the KnownObjects queries
enum class AllocationState : uint32_t {
    Free,
    Reserved,
    Allocated,
};

template <typename T>
struct ObjectDataBase {
    // The backend-provided handle and generation to this object.
    T handle = nullptr;
    ObjectGeneration generation = 0;

    AllocationState state;
};

// Stores what the backend knows about the type.
template <typename T>
struct ObjectData : public ObjectDataBase<T> {};

enum class BufferMapWriteState { Unmapped, Mapped, MapError };

template <>
struct ObjectData<WGPUBuffer> : public ObjectDataBase<WGPUBuffer> {
    // TODO(enga): Use a tagged pointer to save space.
    std::unique_ptr<MemoryTransferService::ReadHandle> readHandle;
    std::unique_ptr<MemoryTransferService::WriteHandle> writeHandle;
    BufferMapWriteState mapWriteState = BufferMapWriteState::Unmapped;
    WGPUBufferUsageFlags usage = WGPUBufferUsage_None;
    // Indicate if writeHandle needs to be destroyed on unmap
    bool mappedAtCreation = false;
};

struct DeviceInfo {
    raw_ptr<Server> server;
    ObjectHandle self;
};

template <>
struct ObjectData<WGPUDevice> : public ObjectDataBase<WGPUDevice> {
    // Store |info| as a separate allocation so that its address does not move.
    // The pointer to |info| is used as the userdata to device callback.
    std::unique_ptr<DeviceInfo> info = std::make_unique<DeviceInfo>();
};

// Information of both an ID and an object data for use as a shorthand in doers. Reserved objects
// are guaranteed to have been reserved, but not guaranteed to be backed by a valid backend handle.
template <typename T>
struct Reserved {
    ObjectId id;
    raw_ptr<ObjectData<T>> data;

    const ObjectData<T>* operator->() const {
        DAWN_ASSERT(data != nullptr);
        return data;
    }
    ObjectData<T>* operator->() {
        DAWN_ASSERT(data != nullptr);
        return data;
    }

    ObjectHandle AsHandle() const {
        DAWN_ASSERT(data != nullptr);
        return {id, data->generation};
    }
};

// Information of both an ID and an object data for use as a shorthand in doers. Known objects are
// guaranteed to be backed by a valid backend handle.
template <typename T>
struct Known {
    ObjectId id;
    raw_ptr<ObjectData<T>> data;

    const ObjectData<T>* operator->() const {
        DAWN_ASSERT(data != nullptr);
        DAWN_ASSERT(data->state == AllocationState::Allocated);
        return data;
    }
    ObjectData<T>* operator->() {
        DAWN_ASSERT(data != nullptr);
        DAWN_ASSERT(data->state == AllocationState::Allocated);
        return data;
    }

    ObjectHandle AsHandle() const {
        DAWN_ASSERT(data != nullptr);
        DAWN_ASSERT(data->state == AllocationState::Allocated);
        return {id, data->generation};
    }
};

// Keeps track of the mapping between client IDs and backend objects.
template <typename T>
class KnownObjectsBase {
  public:
    using Data = ObjectData<T>;

    KnownObjectsBase() {
        // Reserve ID 0 so that it can be used to represent nullptr for optional object values
        // in the wire format. However don't tag it as allocated so that it is an error to ask
        // KnownObjects for ID 0.
        Data reservation;
        reservation.handle = nullptr;
        reservation.state = AllocationState::Free;
        mKnown.push_back(std::move(reservation));
    }

    // Get a backend objects for a given client ID.
    // Returns an error if the object wasn't previously allocated.
    WireResult GetNativeHandle(ObjectId id, T* handle) const {
        if (id >= mKnown.size()) {
            return WireResult::FatalError;
        }

        const Data* data = &mKnown[id];
        if (data->state != AllocationState::Allocated) {
            return WireResult::FatalError;
        }
        *handle = data->handle;

        return WireResult::Success;
    }

    WireResult Get(ObjectId id, Reserved<T>* result) {
        if (id >= mKnown.size()) {
            return WireResult::FatalError;
        }

        Data* data = &mKnown[id];
        if (data->state == AllocationState::Free) {
            return WireResult::FatalError;
        }

        *result = Reserved<T>{id, data};
        return WireResult::Success;
    }

    WireResult Get(ObjectId id, Known<T>* result) {
        if (id >= mKnown.size()) {
            return WireResult::FatalError;
        }

        Data* data = &mKnown[id];
        if (data->state != AllocationState::Allocated) {
            return WireResult::FatalError;
        }

        *result = Known<T>{id, data};
        return WireResult::Success;
    }

    WireResult FillReservation(ObjectId id, T handle, Known<T>* known = nullptr) {
        DAWN_ASSERT(id < mKnown.size());
        DAWN_ASSERT(handle != nullptr);
        Data* data = &mKnown[id];

        if (data->state != AllocationState::Reserved) {
            return WireResult::FatalError;
        }
        data->handle = handle;
        data->state = AllocationState::Allocated;
        if (known != nullptr) {
            *known = {id, data};
        }
        return WireResult::Success;
    }

    // Allocates the data for a given ID and returns it in result.
    // Returns false if the ID is already allocated, or too far ahead, or if ID is 0 (ID 0 is
    // reserved for nullptr). Invalidates all the Data*
    WireResult Allocate(Reserved<T>* result,
                        ObjectHandle handle,
                        AllocationState state = AllocationState::Allocated) {
        if (handle.id == 0 || handle.id > mKnown.size()) {
            return WireResult::FatalError;
        }

        Data data;
        data.state = state;
        data.handle = nullptr;

        if (handle.id >= mKnown.size()) {
            mKnown.push_back(std::move(data));
            *result = {handle.id, &mKnown.back()};
            return WireResult::Success;
        }

        if (mKnown[handle.id].state != AllocationState::Free) {
            return WireResult::FatalError;
        }

        // The generation should be strictly increasing.
        if (handle.generation <= mKnown[handle.id].generation) {
            return WireResult::FatalError;
        }
        // update the generation in the slot
        data.generation = handle.generation;

        mKnown[handle.id] = std::move(data);

        *result = {handle.id, &mKnown[handle.id]};
        return WireResult::Success;
    }

    // Marks an ID as deallocated
    void Free(ObjectId id) {
        DAWN_ASSERT(id < mKnown.size());
        mKnown[id].state = AllocationState::Free;
    }

    std::vector<T> AcquireAllHandles() {
        std::vector<T> objects;
        for (Data& data : mKnown) {
            if (data.state == AllocationState::Allocated && data.handle != nullptr) {
                objects.push_back(data.handle);
                data.state = AllocationState::Free;
                data.handle = nullptr;
            }
        }

        return objects;
    }

    std::vector<T> GetAllHandles() const {
        std::vector<T> objects;
        for (const Data& data : mKnown) {
            if (data.state == AllocationState::Allocated && data.handle != nullptr) {
                objects.push_back(data.handle);
            }
        }

        return objects;
    }

  protected:
    std::vector<Data> mKnown;
};

template <typename T>
class KnownObjects : public KnownObjectsBase<T> {
  public:
    KnownObjects() = default;
};

template <>
class KnownObjects<WGPUDevice> : public KnownObjectsBase<WGPUDevice> {
  public:
    KnownObjects() = default;

    WireResult Allocate(Reserved<WGPUDevice>* result,
                        ObjectHandle handle,
                        AllocationState state = AllocationState::Allocated) {
        WIRE_TRY(KnownObjectsBase<WGPUDevice>::Allocate(result, handle, state));
        return WireResult::Success;
    }

    WireResult FillReservation(ObjectId id, WGPUDevice handle, Known<WGPUDevice>* known = nullptr) {
        auto result = KnownObjectsBase<WGPUDevice>::FillReservation(id, handle, known);
        if (result == WireResult::Success) {
            mKnownSet.insert((*known)->handle);
        }
        return result;
    }

    void Free(ObjectId id) {
        mKnownSet.erase(mKnown[id].handle);
        KnownObjectsBase<WGPUDevice>::Free(id);
    }

    bool IsKnown(WGPUDevice device) const { return mKnownSet.contains(device); }

  private:
    absl::flat_hash_set<WGPUDevice> mKnownSet;
};

}  // namespace dawn::wire::server

#endif  // SRC_DAWN_WIRE_SERVER_OBJECTSTORAGE_H_