chromium/base/memory/discardable_shared_memory.h

// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_MEMORY_DISCARDABLE_SHARED_MEMORY_H_
#define BASE_MEMORY_DISCARDABLE_SHARED_MEMORY_H_

#include <stddef.h>

#include "base/base_export.h"
#include "base/containers/span.h"
#include "base/dcheck_is_on.h"
#include "base/memory/shared_memory_mapping.h"
#include "base/memory/unsafe_shared_memory_region.h"
#include "base/threading/thread_collision_warner.h"
#include "base/time/time.h"
#include "build/build_config.h"

#if DCHECK_IS_ON()
#include <set>
#endif

// Linux (including Android) support the MADV_REMOVE argument with madvise()
// which has the behavior of reliably causing zero-fill-on-demand pages to
// be returned after a call. Here we define
// DISCARDABLE_SHARED_MEMORY_ZERO_FILL_ON_DEMAND_PAGES_AFTER_PURGE on Linux
// and Android to indicate that this type of behavior can be expected on
// those platforms. Note that madvise() will still be used on other POSIX
// platforms but doesn't provide the zero-fill-on-demand pages guarantee.
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS) || BUILDFLAG(IS_ANDROID)
#define DISCARDABLE_SHARED_MEMORY_ZERO_FILL_ON_DEMAND_PAGES_AFTER_PURGE
#endif

namespace base {

namespace trace_event {
class MemoryAllocatorDump;
class ProcessMemoryDump;
}  // namespace trace_event

// Platform abstraction for discardable shared memory.
//
// This class is not thread-safe. Clients are responsible for synchronizing
// access to an instance of this class.
class BASE_EXPORT DiscardableSharedMemory { … };

}  // namespace base

#endif  // BASE_MEMORY_DISCARDABLE_SHARED_MEMORY_H_