src/dawn/native/DeviceGuard.h

// Copyright 2025 The Dawn & Tint Authors
//
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#ifndef SRC_DAWN_NATIVE_DEVICEGUARD_H_
#define SRC_DAWN_NATIVE_DEVICEGUARD_H_

#include <mutex>
#include <optional>

#include "dawn/common/Compiler.h"
#include "dawn/common/Defer.h"
#include "dawn/common/MutexProtected.h"
#include "dawn/common/Ref.h"

namespace dawn::native {

class DeviceBase;

class DeviceMutex : public RecursiveMutex {
  public:
    ~DeviceMutex() override;

  private:
    friend class DeviceBase;
    friend struct AutoLockBase<DeviceMutex*>;

    void Lock() DAWN_EXCLUSIVE_LOCK_FUNCTION;
    void Unlock() DAWN_UNLOCK_FUNCTION;

    uint32_t mRecursionStackDepth = 0;
    std::optional<class Defer> mDefer = std::nullopt;
};

namespace detail {

struct DeviceMutexTraits {
    using MutexType = Ref<DeviceMutex>;
    using LockType = DeviceMutex::AutoLockBase<DeviceMutex*>;

    static DeviceMutex* GetMutex(MutexType& m) { return m.Get(); }
    static DeviceBase* GetObj(DeviceBase* const d) { return d; }
    static const DeviceBase* GetObj(const DeviceBase* const d) { return d; }
};

// This base class is necessary for destructor ordering in the implementing DeviceGuard class
// below.
class DeviceGuardBase {
  protected:
    explicit DeviceGuardBase(DeviceMutex* mutex = nullptr);
    DeviceGuardBase(DeviceGuardBase&&) = default;

  private:
    // Optionally, this base class may hold a strong reference to the actual mutex. This is used
    // when the Device which is the owner of the mutex may be deleted while still holding the mutex.
    Ref<DeviceMutex> mMutex = nullptr;
};

}  // namespace detail

// DeviceGuard is the equivalent to a Guard when using MutexProtected specifically designed for the
// device-wide lock. Usually, Guards are scoped via lambda functions, but for the device-wide lock,
// we provide ways to get this guard and call Defer from the Device. Since the device-wide lock is a
// temporary solution, this provides a way get the guard without adding lambda scopes everywhere.
class DeviceGuard : public detail::DeviceGuardBase,
                    private ::dawn::detail::Guard<DeviceBase, detail::DeviceMutexTraits> {
  public:
    using GuardBase = ::dawn::detail::Guard<DeviceBase, detail::DeviceMutexTraits>;

    DeviceGuard(DeviceGuard&&);

  private:
    friend class DeviceBase;

    explicit DeviceGuard(DeviceBase* device, DeviceMutex* mutex = nullptr);
};

}  // namespace dawn::native

#endif  // SRC_DAWN_NATIVE_DEVICEGUARD_H_