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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 ProfileBufferChunkManagerSingle_h
#define ProfileBufferChunkManagerSingle_h
#include "mozilla/ProfileBufferChunkManager.h"
#ifdef DEBUG
# include "mozilla/Atomics.h"
#endif // DEBUG
namespace mozilla {
// Manages only one Chunk.
// The first call to `Get`/`RequestChunk()` will retrieve the one chunk, and all
// subsequent calls will return nullptr. That chunk may still be released, but
// it will never be destroyed or recycled.
// Unlike others, this manager may be `Reset()`, to allow another round of
// small-data gathering.
// The main use is with short-lived ProfileChunkedBuffers that collect little
// data that can fit in one chunk, e.g., capturing one stack.
// It is not thread-safe.
class ProfileBufferChunkManagerSingle final : public ProfileBufferChunkManager {
using Length = ProfileBufferChunk::Length;
// Use a preallocated chunk. (Accepting null to gracefully handle OOM.)
explicit ProfileBufferChunkManagerSingle(UniquePtr<ProfileBufferChunk> aChunk)
: mInitialChunk(std::move(aChunk)),
mBufferBytes(mInitialChunk ? mInitialChunk->BufferBytes() : 0) {
MOZ_ASSERT(!mInitialChunk || !mInitialChunk->GetNext(),
"Expected at most one chunk");
// ChunkMinBufferBytes: Minimum number of user-available bytes in the Chunk.
// Note that Chunks use a bit more memory for their header.
explicit ProfileBufferChunkManagerSingle(Length aChunkMinBufferBytes)
: mInitialChunk(ProfileBufferChunk::Create(aChunkMinBufferBytes)),
mBufferBytes(mInitialChunk ? mInitialChunk->BufferBytes() : 0) {}
#ifdef DEBUG
~ProfileBufferChunkManagerSingle() { MOZ_ASSERT(mVirtuallyLocked == false); }
#endif // DEBUG
// Reset this manager, using the provided chunk (probably coming from the
// ProfileChunkedBuffer that just used it); if null, fallback on current or
// released chunk.
void Reset(UniquePtr<ProfileBufferChunk> aPossibleChunk) {
if (aPossibleChunk) {
mInitialChunk = std::move(aPossibleChunk);
mReleasedChunk = nullptr;
} else if (!mInitialChunk) {
MOZ_ASSERT(!!mReleasedChunk, "Can't reset properly!");
mInitialChunk = std::move(mReleasedChunk);
if (mInitialChunk) {
mBufferBytes = mInitialChunk->BufferBytes();
} else {
mBufferBytes = 0;
[[nodiscard]] size_t MaxTotalSize() const final { return mBufferBytes; }
// One of `GetChunk` and `RequestChunk` will only work the very first time (if
// there's even a chunk).
[[nodiscard]] UniquePtr<ProfileBufferChunk> GetChunk() final {
MOZ_ASSERT(mUser, "Not registered yet");
return std::move(mInitialChunk);
void RequestChunk(std::function<void(UniquePtr<ProfileBufferChunk>)>&&
aChunkReceiver) final {
MOZ_ASSERT(mUser, "Not registered yet");
// Simple retrieval.
void FulfillChunkRequests() final {
// Nothing to do here.
void ReleaseChunk(UniquePtr<ProfileBufferChunk> aChunk) final {
MOZ_ASSERT(mUser, "Not registered yet");
if (!aChunk) {
MOZ_ASSERT(!mReleasedChunk, "Unexpected 2nd released chunk");
MOZ_ASSERT(!aChunk->GetNext(), "Only expected one released chunk");
mReleasedChunk = std::move(aChunk);
void SetChunkDestroyedCallback(
std::function<void(const ProfileBufferChunk&)>&& aChunkDestroyedCallback)
final {
MOZ_ASSERT(mUser, "Not registered yet");
// The chunk-destroyed callback will never actually be called, but we keep
// the callback here in case the caller expects it to live as long as this
// manager.
mChunkDestroyedCallback = std::move(aChunkDestroyedCallback);
[[nodiscard]] UniquePtr<ProfileBufferChunk> GetExtantReleasedChunks() final {
MOZ_ASSERT(mUser, "Not registered yet");
return std::move(mReleasedChunk);
void ForgetUnreleasedChunks() final {
MOZ_ASSERT(mUser, "Not registered yet");
[[nodiscard]] size_t SizeOfExcludingThis(
MallocSizeOf aMallocSizeOf) const final {
MOZ_ASSERT(mUser, "Not registered yet");
size_t size = 0;
if (mInitialChunk) {
size += mInitialChunk->SizeOfIncludingThis(aMallocSizeOf);
if (mReleasedChunk) {
size += mReleasedChunk->SizeOfIncludingThis(aMallocSizeOf);
// Note: Missing size of std::function external resources (if any).
return size;
[[nodiscard]] size_t SizeOfIncludingThis(
MallocSizeOf aMallocSizeOf) const final {
MOZ_ASSERT(mUser, "Not registered yet");
return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
// This manager is not thread-safe, so there's not actual locking needed.
const ProfileBufferChunk* PeekExtantReleasedChunksAndLock() final {
MOZ_ASSERT(mVirtuallyLocked.compareExchange(false, true));
MOZ_ASSERT(mUser, "Not registered yet");
return mReleasedChunk.get();
void UnlockAfterPeekExtantReleasedChunks() final {
MOZ_ASSERT(mVirtuallyLocked.compareExchange(true, false));
// Initial chunk created with this manager, given away at first Get/Request.
UniquePtr<ProfileBufferChunk> mInitialChunk;
// Storage for the released chunk (which should probably not happen, as it
// means the chunk is full).
UniquePtr<ProfileBufferChunk> mReleasedChunk;
// Size of the one chunk we're managing. Stored here, because the chunk may
// be moved out and inaccessible from here.
Length mBufferBytes;
// The chunk-destroyed callback will never actually be called, but we keep it
// here in case the caller expects it to live as long as this manager.
std::function<void(const ProfileBufferChunk&)> mChunkDestroyedCallback;
#ifdef DEBUG
mutable Atomic<bool> mVirtuallyLocked{false};
#endif // DEBUG
} // namespace mozilla
#endif // ProfileBufferChunkManagerSingle_h