citra/src/video_core/gpu_thread.h

// Copyright 2019 yuzu Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#pragma once

#include <array>
#include <atomic>
#include <condition_variable>
#include <memory>
#include <mutex>
#include <optional>
#include <thread>
#include <variant>

namespace Tegra {
struct FramebufferConfig;
class DmaPusher;
} // namespace Tegra

namespace VideoCore {
class RendererBase;
} // namespace VideoCore

namespace VideoCommon::GPUThread {

/// Command to signal to the GPU thread that a command list is ready for processing
struct SubmitListCommand final {
    explicit SubmitListCommand(Tegra::CommandList&& entries) : entries{std::move(entries)} {}

    Tegra::CommandList entries;
};

/// Command to signal to the GPU thread that a swap buffers is pending
struct SwapBuffersCommand final {
    explicit SwapBuffersCommand(std::optional<const Tegra::FramebufferConfig> framebuffer)
        : framebuffer{std::move(framebuffer)} {}

    std::optional<const Tegra::FramebufferConfig> framebuffer;
};

/// Command to signal to the GPU thread to flush a region
struct FlushRegionCommand final {
    explicit constexpr FlushRegionCommand(VAddr addr, u64 size) : addr{addr}, size{size} {}

    const VAddr addr;
    const u64 size;
};

/// Command to signal to the GPU thread to invalidate a region
struct InvalidateRegionCommand final {
    explicit constexpr InvalidateRegionCommand(VAddr addr, u64 size) : addr{addr}, size{size} {}

    const VAddr addr;
    const u64 size;
};

/// Command to signal to the GPU thread to flush and invalidate a region
struct FlushAndInvalidateRegionCommand final {
    explicit constexpr FlushAndInvalidateRegionCommand(VAddr addr, u64 size)
        : addr{addr}, size{size} {}

    const VAddr addr;
    const u64 size;
};

using CommandData = std::variant<SubmitListCommand, SwapBuffersCommand, FlushRegionCommand,
                                 InvalidateRegionCommand, FlushAndInvalidateRegionCommand>;

/// Struct used to synchronize the GPU thread
struct SynchState final {
    std::atomic<bool> is_running{true};
    std::atomic<bool> is_idle{true};
    std::condition_variable signal_condition;
    std::mutex signal_mutex;
    std::condition_variable idle_condition;
    std::mutex idle_mutex;

    // We use two queues for sending commands to the GPU thread, one for writing (push_queue) to and
    // one for reading from (pop_queue). These are swapped whenever the current pop_queue becomes
    // empty. This allows for efficient thread-safe access, as it does not require any copies.

    using CommandQueue = std::queue<CommandData>;
    std::array<CommandQueue, 2> command_queues;
    CommandQueue* push_queue{&command_queues[0]};
    CommandQueue* pop_queue{&command_queues[1]};

    void UpdateIdleState() {
        std::lock_guard<std::mutex> lock{idle_mutex};
        is_idle = command_queues[0].empty() && command_queues[1].empty();
    }
};

/// Class used to manage the GPU thread
class ThreadManager final {
public:
    explicit ThreadManager(VideoCore::RendererBase& renderer, Tegra::DmaPusher& dma_pusher);
    ~ThreadManager();

    /// Push GPU command entries to be processed
    void SubmitList(Tegra::CommandList&& entries);

    /// Swap buffers (render frame)
    void SwapBuffers(
        std::optional<std::reference_wrapper<const Tegra::FramebufferConfig>> framebuffer);

    /// Notify rasterizer that any caches of the specified region should be flushed to Switch memory
    void FlushRegion(VAddr addr, u64 size);

    /// Notify rasterizer that any caches of the specified region should be invalidated
    void InvalidateRegion(VAddr addr, u64 size);

    /// Notify rasterizer that any caches of the specified region should be flushed and invalidated
    void FlushAndInvalidateRegion(VAddr addr, u64 size);

    /// Waits the caller until the GPU thread is idle, used for synchronization
    void WaitForIdle();

private:
    /// Pushes a command to be executed by the GPU thread
    void PushCommand(CommandData&& command_data, bool wait_for_idle, bool allow_on_cpu);

    /// Returns true if this is called by the GPU thread
    bool IsGpuThread() const {
        return std::this_thread::get_id() == thread_id;
    }

private:
    SynchState state;
    std::thread thread;
    std::thread::id thread_id;
    VideoCore::RendererBase& renderer;
    Tegra::DmaPusher& dma_pusher;
};

} // namespace VideoCommon::GPUThread