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

namespace dawn::native {

class DeviceBase;

namespace detail {

struct DeviceMutexTraits {
    using MutexType = Ref<RecursiveMutex>;
    using LockType = RecursiveMutex::AutoLock;

    static RecursiveMutex* 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. The Defer object must be deleted after the lock is released, and since the lock is only
// released when the Guard is destroyed, the implementing class below must extend this class before
// extending the Guard class to enforce the correct destructor ordering.
class DeviceGuardBase {
  protected:
    explicit DeviceGuardBase(RecursiveMutex* mutex = nullptr);

  protected:
    // Since guards are always stack allocated, they must be cleaned up in the reverse order of
    // creation. That said, the first guard to be created in a given stack will always be the guard
    // to resolve the defers. The fields below are actually set by the implementing class
    // DeviceGuard to ensure that the Device lock has been acquired before any modifitcations. The
    // actual Defer object will be moved into mDefer if necessary by the ~DeviceGuard, again because
    // we don't want to modify state without the lock, but we want to destroy the Defer object
    // without the lock.
    bool mHandleDefer = false;
    std::optional<class Defer> mDefer = std::nullopt;

  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<RecursiveMutex> 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();

  private:
    friend class DeviceBase;

    // Explicitly make mDefer from detail::DeviceGuardBase visible since the Guard class also has a
    // mDefer member.
    using detail::DeviceGuardBase::mDefer;

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

}  // namespace dawn::native

#endif  // SRC_DAWN_NATIVE_DEVICEGUARD_H_