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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef ProfileBufferControlledChunkManager_h
#define ProfileBufferControlledChunkManager_h
#include "mozilla/ProfileBufferChunk.h"
#include <functional>
#include <vector>
namespace mozilla {
// A "Controlled" chunk manager will provide updates about chunks that it
// creates, releases, and destroys; and it can destroy released chunks as
// requested.
class ProfileBufferControlledChunkManager {
using Length = ProfileBufferChunk::Length;
virtual ~ProfileBufferControlledChunkManager() = default;
// Minimum amount of chunk metadata to be transferred between processes.
struct ChunkMetadata {
// Timestamp when chunk was marked "done", which is used to:
// - determine its age, so the oldest one will be destroyed first,
// - uniquely identify this chunk in this process. (The parent process is
// responsible for associating this timestamp to its process id.)
TimeStamp mDoneTimeStamp;
// Size of this chunk's buffer.
Length mBufferBytes;
ChunkMetadata(TimeStamp aDoneTimeStamp, Length aBufferBytes)
: mDoneTimeStamp(aDoneTimeStamp), mBufferBytes(aBufferBytes) {}
// Class collecting all information necessary to describe updates that
// happened in a chunk manager.
// An update can be folded into a previous update.
class Update {
// Construct a "not-an-Update" object, which should only be used after a
// real update is folded into it.
Update() = default;
// Construct a "final" Update, which marks the end of all updates from a
// chunk manager.
explicit Update(decltype(nullptr)) : mUnreleasedBytes(FINAL) {}
// Construct an Update from the given data and released chunks.
// The chunk pointers may be null, and it doesn't matter if
// `aNewlyReleasedChunks` is already linked to `aExistingReleasedChunks` or
// not.
Update(size_t aUnreleasedBytes, size_t aReleasedBytes,
const ProfileBufferChunk* aExistingReleasedChunks,
const ProfileBufferChunk* aNewlyReleasedChunks)
: mUnreleasedBytes(aUnreleasedBytes),
? aExistingReleasedChunks->ChunkHeader().mDoneTimeStamp
: TimeStamp{}) {
"Empty update should only be constructed with default constructor");
"Final update should only be constructed with nullptr constructor");
for (const ProfileBufferChunk* chunk = aNewlyReleasedChunks; chunk;
chunk = chunk->GetNext()) {
chunk->ChunkHeader().mDoneTimeStamp, chunk->BufferBytes()});
// Construct an Update from raw data.
// This may be used to re-construct an Update that was previously
// serialized.
Update(size_t aUnreleasedBytes, size_t aReleasedBytes,
TimeStamp aOldestDoneTimeStamp,
std::vector<ChunkMetadata>&& aNewlyReleasedChunks)
: mUnreleasedBytes(aUnreleasedBytes),
mNewlyReleasedChunks(std::move(aNewlyReleasedChunks)) {}
// Clear the Update completely and return it to a "not-an-Update" state.
void Clear() {
mUnreleasedBytes = NO_UPDATE;
mReleasedBytes = 0;
mOldestDoneTimeStamp = TimeStamp{};
bool IsNotUpdate() const { return mUnreleasedBytes == NO_UPDATE; }
bool IsFinal() const { return mUnreleasedBytes == FINAL; }
size_t UnreleasedBytes() const {
"Cannot access UnreleasedBytes from empty update");
"Cannot access UnreleasedBytes from final update");
return mUnreleasedBytes;
size_t ReleasedBytes() const {
"Cannot access ReleasedBytes from empty update");
"Cannot access ReleasedBytes from final update");
return mReleasedBytes;
TimeStamp OldestDoneTimeStamp() const {
"Cannot access OldestDoneTimeStamp from empty update");
"Cannot access OldestDoneTimeStamp from final update");
return mOldestDoneTimeStamp;
const std::vector<ChunkMetadata>& NewlyReleasedChunksRef() const {
"Cannot access NewlyReleasedChunksRef from empty update");
!IsFinal(), "Cannot access NewlyReleasedChunksRef from final update");
return mNewlyReleasedChunks;
// Fold a later update into this one.
void Fold(Update&& aNewUpdate) {
!IsFinal() || aNewUpdate.IsFinal(),
"There shouldn't be another non-final update after the final update");
if (IsNotUpdate() || aNewUpdate.IsFinal()) {
// We were empty, or the new update is the final update, we just switch
// to that new update.
*this = std::move(aNewUpdate);
mUnreleasedBytes = aNewUpdate.mUnreleasedBytes;
mReleasedBytes = aNewUpdate.mReleasedBytes;
if (!aNewUpdate.mOldestDoneTimeStamp.IsNull()) {
MOZ_ASSERT(mOldestDoneTimeStamp.IsNull() ||
mOldestDoneTimeStamp <= aNewUpdate.mOldestDoneTimeStamp);
mOldestDoneTimeStamp = aNewUpdate.mOldestDoneTimeStamp;
auto it = mNewlyReleasedChunks.begin();
while (it != mNewlyReleasedChunks.end() &&
it->mDoneTimeStamp < mOldestDoneTimeStamp) {
it = mNewlyReleasedChunks.erase(it);
if (!aNewUpdate.mNewlyReleasedChunks.empty()) {
mNewlyReleasedChunks.reserve(mNewlyReleasedChunks.size() +
static const size_t NO_UPDATE = size_t(-1);
static const size_t FINAL = size_t(-2);
size_t mUnreleasedBytes = NO_UPDATE;
size_t mReleasedBytes = 0;
TimeStamp mOldestDoneTimeStamp;
std::vector<ChunkMetadata> mNewlyReleasedChunks;
using UpdateCallback = std::function<void(Update&&)>;
// This *may* be set (or reset) by an object that needs to know about all
// chunk updates that happen in this manager. The main use will be to
// coordinate the global memory usage of Firefox.
// If a non-empty callback is given, it will be immediately invoked with the
// current state.
// When the callback is about to be destroyed (by overwriting it here, or in
// the class destructor), it will be invoked one last time with an empty
// update.
// Note that the callback (even the first current-state callback) will be
// invoked from inside a locked scope, so it should *not* call other functions
// of the chunk manager. A side benefit of this locking is that it guarantees
// that no two invocations can overlap.
virtual void SetUpdateCallback(UpdateCallback&& aUpdateCallback) = 0;
// This is a request to destroy all chunks before the given timestamp.
// This timestamp should be one that was given in a previous UpdateCallback
// call. Obviously, only released chunks can be destroyed.
virtual void DestroyChunksAtOrBefore(TimeStamp aDoneTimeStamp) = 0;
} // namespace mozilla
#endif // ProfileBufferControlledChunkManager_h