chromium/gpu/command_buffer/common/discardable_handle.h

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef GPU_COMMAND_BUFFER_COMMON_DISCARDABLE_HANDLE_H_
#define GPU_COMMAND_BUFFER_COMMON_DISCARDABLE_HANDLE_H_

#include "base/memory/ref_counted.h"
#include "base/types/id_type.h"
#include "gpu/gpu_export.h"

namespace gpu {

class Buffer;

struct SerializableSkiaHandle { … };

// DiscardableHandleBase is the base class for the discardable handle
// implementation. In order to facilitate transfering handles across the
// command buffer, DiscardableHandleBase is backed by a gpu::Buffer and an
// offset into that buffer. It uses a single uint32_t of data at the given
// offset.
//
// DiscardableHandleBase is never used directly, but is instead modified by the
// Client/ServiceDiscardableHandle subclasses. These subclasses implement the
// Lock/Unlock/Delete functionality, making it explicit which operations occur
// in which process.
//
// Via these subclasses, a discardable handle can be transitioned between one
// of three states:
//  ╔════════════╗         ╔════════════╗         ╔═══════════╗
//  ║   Locked   ║ ──────> ║  Unlocked  ║ ──────> ║  Deleted  ║
//  ╚════════════╝         ╚════════════╝         ╚═══════════╝
//         └───────────<──────────┘
//
// Note that a handle can be locked multiple times, and stores a lock-count.
class GPU_EXPORT DiscardableHandleBase { … };

// ClientDiscardableHandle enables the instantiation of a new discardable
// handle (via the constructor), and can Lock an existing handle.
class GPU_EXPORT ClientDiscardableHandle : public DiscardableHandleBase { … };

// ServiceDiscardableHandle can wrap an existing handle (via the constructor),
// and can unlock and delete this handle.
class GPU_EXPORT ServiceDiscardableHandle : public DiscardableHandleBase { … };

}  // namespace gpu

#endif  // GPU_COMMAND_BUFFER_COMMON_DISCARDABLE_HANDLE_H_