src/gpu/AsyncReadTypes.h

/*
 * Copyright 2019 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#ifndef skgpu_AsyncReadTypes_DEFINED
#define skgpu_AsyncReadTypes_DEFINED

#include "include/core/SkData.h"
#include "include/core/SkImage.h"
#include "include/core/SkRefCnt.h"
#include "include/core/SkSize.h"
#include "include/private/SkAssert.h"
#include "include/private/SkDebug.h"
#include "include/private/SkTArray.h"
#include "src/core/SkMessageBus.h"

#include <cstddef>
#include <forward_list>
#include <utility>

namespace skgpu {
/**
 * We sometimes hand clients objects that contain mapped buffers. The client may consume
 * the mapped buffer on another thread. This object manages receiving messages that buffers are
 * ready to be unmapped (on the owner's thread). It also handles cleaning up mapped
 * buffers if the owner is destroyed before the client has finished with the buffer.
 *
 * Buffers are first registered using insert() before being passed the client. process() should be
 * called periodically on the owner's thread to poll for messages and process them.
 */
template <typename T, typename IDType>
class TClientMappedBufferManager {
public:
    /**
     * The message type that internal users of this should post to unmap the buffer.
     * Set fInboxID to inboxID(). fBuffer must have been previously passed to insert().
     */
    struct BufferFinishedMessage {
        BufferFinishedMessage(sk_sp<T> buffer,
                              IDType intendedRecipient)
                : fBuffer(std::move(buffer)), fIntendedRecipient(intendedRecipient) {}
        BufferFinishedMessage(BufferFinishedMessage&& other) {
            fBuffer = std::move(other.fBuffer);
            fIntendedRecipient = other.fIntendedRecipient;
            other.fIntendedRecipient.makeInvalid();
        }
        sk_sp<T> fBuffer;
        IDType   fIntendedRecipient;
    };
    using BufferFinishedMessageBus = SkMessageBus<BufferFinishedMessage,
                                                  IDType,
                                                  false>;

    TClientMappedBufferManager(IDType ownerID)
            : fFinishedBufferInbox(ownerID) {}
    TClientMappedBufferManager(const TClientMappedBufferManager&) = delete;
    TClientMappedBufferManager(TClientMappedBufferManager&&) = delete;

    ~TClientMappedBufferManager() {
        this->process();
        if (!fAbandoned) {
            // If we're going down before we got the messages we go ahead and unmap all the buffers.
            // It's up to the client to ensure that they aren't being accessed on another thread
            // while this is happening (or afterwards on any thread).
            for (auto& b : fClientHeldBuffers) {
                b->unmap();
            }
        }
    }

    TClientMappedBufferManager& operator=(const TClientMappedBufferManager&) = delete;
    TClientMappedBufferManager& operator=(TClientMappedBufferManager&&) = delete;

    /** Initialize BufferFinishedMessage::fIntendedRecipient to this value. It is the
     *  unique ID of the object that owns this buffer manager.
     */
    IDType ownerID() const {
        return fFinishedBufferInbox.uniqueID();
    }

    /**
     * Let the manager know to expect a message with buffer 'b'. It's illegal for a buffer to be
     * inserted again before it is unmapped by process().
     */
    void insert(sk_sp<T> b) {
        SkDEBUGCODE(auto end = fClientHeldBuffers.end());
        SkASSERT(std::find(fClientHeldBuffers.begin(), end, b) == end);
        fClientHeldBuffers.emplace_front(std::move(b));
    }

    /** Poll for messages and unmap any incoming buffers. */
    void process() {
        skia_private::STArray<4, BufferFinishedMessage> messages;
        fFinishedBufferInbox.poll(&messages);
        if (!fAbandoned) {
            for (auto& m : messages) {
                this->remove(m.fBuffer);
                m.fBuffer->unmap();
            }
        }
    }

    /** Notifies the manager that the context has been abandoned. No more unmaps() will occur.*/
    void abandon() {
        fAbandoned = true;
        fClientHeldBuffers.clear();
    }

private:
    typename BufferFinishedMessageBus::Inbox fFinishedBufferInbox;
    std::forward_list<sk_sp<T>> fClientHeldBuffers;
    bool fAbandoned = false;

    void remove(const sk_sp<T>& b) {
        // There is no convenient remove only the first element that equals a value functionality in
        // std::forward_list.
        auto prev = fClientHeldBuffers.before_begin();
        auto end = fClientHeldBuffers.end();
        SkASSERT(std::find(fClientHeldBuffers.begin(), end, b) != end);
        for (auto cur = fClientHeldBuffers.begin(); cur != end; prev = cur++) {
            if (*cur == b) {
                fClientHeldBuffers.erase_after(prev);
                break;
            }
        }
        SkASSERT(std::find(fClientHeldBuffers.begin(), end, b) == end);
    }
};

////////////////////////////////////////////////////////////////////////////////

template <typename T, typename IDType, typename TransferResultType>
class TAsyncReadResult : public SkImage::AsyncReadResult {
public:
    TAsyncReadResult(IDType intendedRecipient)
        : fIntendedRecipient(intendedRecipient) {
    }

    ~TAsyncReadResult() override {
        for (int i = 0; i < fPlanes.size(); ++i) {
            fPlanes[i].releaseMappedBuffer(fIntendedRecipient);
        }
    }

    int count() const override { return fPlanes.size(); }
    const void* data(int i) const override { return fPlanes[i].data(); }
    size_t rowBytes(int i) const override { return fPlanes[i].rowBytes(); }

    bool addTransferResult(const TransferResultType& result,
                           SkISize dimensions,
                           size_t rowBytes,
                           TClientMappedBufferManager<T, IDType>* manager) {
        const void* mappedData = result.fTransferBuffer->map();
        if (!mappedData) {
            return false;
        }
        if (result.fPixelConverter) {
            size_t size = rowBytes*dimensions.height();
            sk_sp<SkData> data = SkData::MakeUninitialized(size);
            result.fPixelConverter(data->writable_data(), mappedData);
            this->addCpuPlane(std::move(data), rowBytes);
            result.fTransferBuffer->unmap();
        } else {
            manager->insert(result.fTransferBuffer);
            this->addMappedPlane(mappedData, rowBytes, std::move(result.fTransferBuffer));
        }
        return true;
    }

    void addCpuPlane(sk_sp<SkData> data, size_t rowBytes) {
        SkASSERT(data);
        SkASSERT(rowBytes > 0);
        fPlanes.emplace_back(std::move(data), rowBytes);
    }

private:
    void addMappedPlane(const void* data, size_t rowBytes, sk_sp<T> mappedBuffer) {
        SkASSERT(data);
        SkASSERT(rowBytes > 0);
        SkASSERT(mappedBuffer);
        SkASSERT(mappedBuffer->isMapped());
        fPlanes.emplace_back(std::move(mappedBuffer), rowBytes);
    }

    class Plane {
    public:
        Plane(sk_sp<T> buffer, size_t rowBytes)
                : fMappedBuffer(std::move(buffer)), fRowBytes(rowBytes) {}
        Plane(sk_sp<SkData> data, size_t rowBytes) : fData(std::move(data)), fRowBytes(rowBytes) {}

        Plane(Plane&&) = default;

        ~Plane() { SkASSERT(!fMappedBuffer); }

        Plane& operator=(const Plane&) = delete;
        Plane& operator=(Plane&&) = default;

        void releaseMappedBuffer(IDType intendedRecipient) {
            if (fMappedBuffer) {
                TClientMappedBufferManager<T, IDType>::BufferFinishedMessageBus::Post(
                        {std::move(fMappedBuffer), intendedRecipient});
            }
        }

        const void* data() const {
            if (fMappedBuffer) {
                SkASSERT(!fData);
                SkASSERT(fMappedBuffer->isMapped());
                return fMappedBuffer->map();
            }
            SkASSERT(fData);
            return fData->data();
        }

        size_t rowBytes() const { return fRowBytes; }

    private:
        sk_sp<SkData> fData;
        sk_sp<T> fMappedBuffer;
        size_t fRowBytes;
    };
    skia_private::STArray<4, Plane> fPlanes;
    IDType fIntendedRecipient;
};

}  // namespace skgpu

#endif  // skgpu_AsyncReadTypes_DEFINED