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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 ProfileBufferChunkManager_h
#define ProfileBufferChunkManager_h
#include "mozilla/ProfileBufferChunk.h"
#include "mozilla/ScopeExit.h"
#include <functional>
namespace mozilla {
// Manages the ProfileBufferChunks for this process.
// The main user of this class is the buffer that needs chunks to store its
// data.
// The main ProfileBufferChunks responsibilities are:
// - It can create new chunks, they are called "unreleased".
// - Later these chunks are returned here, and become "released".
// - The manager is free to destroy or recycle the oldest released chunks
// (usually to reclaim memory), and will inform the user through a provided
// callback.
// - The user may access still-alive released chunks.
class ProfileBufferChunkManager {
virtual ~ProfileBufferChunkManager()
#ifdef DEBUG
MOZ_ASSERT(!mUser, "Still registered when being destroyed");
= default;
// Expected maximum size needed to store one stack sample.
// Most ChunkManager sub-classes will require chunk sizes, this can serve as
// a minimum recommendation to hold most backtraces.
constexpr static ProfileBufferChunk::Length scExpectedMaximumStackSize =
128 * 1024;
// Estimated maximum buffer size.
[[nodiscard]] virtual size_t MaxTotalSize() const = 0;
// Create or recycle a chunk right now. May return null in case of allocation
// failure.
// Note that the chunk-destroyed callback may be invoked during this call;
// user should be careful with reentrancy issues.
[[nodiscard]] virtual UniquePtr<ProfileBufferChunk> GetChunk() = 0;
// `aChunkReceiver` may be called with a new or recycled chunk, or nullptr.
// (See `FulfillChunkRequests()` regarding when the callback may happen.)
virtual void RequestChunk(
std::function<void(UniquePtr<ProfileBufferChunk>)>&& aChunkReceiver) = 0;
// This method may be invoked at any time on any thread (and not necessarily
// by the main user of this class), to do the work necessary to respond to a
// previous `RequestChunk()`.
// It is optional: If it is never called, or called too late, the user is
// responsible for directly calling `GetChunk()` when a chunk is really
// needed (or it should at least fail gracefully).
// The idea is to fulfill chunk request on a separate thread, and most
// importantly outside of profiler calls, to avoid doing expensive memory
// allocations during these calls.
virtual void FulfillChunkRequests() = 0;
// One chunk is released by the user, the ProfileBufferChunkManager should
// keep it as long as possible (depending on local or global memory/time
// limits). Note that the chunk-destroyed callback may be invoked during this
// call; user should be careful with reentrancy issues.
virtual void ReleaseChunk(UniquePtr<ProfileBufferChunk> aChunk) = 0;
// `aChunkDestroyedCallback` will be called whenever the contents of a
// previously-released chunk is about to be destroyed or recycled.
// Note that it may be called during other functions above, or at other times
// from the same or other threads; user should be careful with reentrancy
// issues.
virtual void SetChunkDestroyedCallback(
std::function<void(const ProfileBufferChunk&)>&&
aChunkDestroyedCallback) = 0;
// Give away all released chunks that have not yet been destroyed.
[[nodiscard]] virtual UniquePtr<ProfileBufferChunk>
GetExtantReleasedChunks() = 0;
// Let a callback see all released chunks that have not yet been destroyed, if
// any. Return whatever the callback returns.
template <typename Callback>
[[nodiscard]] auto PeekExtantReleasedChunks(Callback&& aCallback) {
const ProfileBufferChunk* chunks = PeekExtantReleasedChunksAndLock();
auto unlock =
MakeScopeExit([&]() { UnlockAfterPeekExtantReleasedChunks(); });
return std::forward<Callback>(aCallback)(chunks);
// Chunks that were still unreleased will never be released.
virtual void ForgetUnreleasedChunks() = 0;
[[nodiscard]] virtual size_t SizeOfExcludingThis(
MallocSizeOf aMallocSizeOf) const = 0;
[[nodiscard]] virtual size_t SizeOfIncludingThis(
MallocSizeOf aMallocSizeOf) const = 0;
// Derived classes to implement `PeekExtantReleasedChunks` through these:
virtual const ProfileBufferChunk* PeekExtantReleasedChunksAndLock() = 0;
virtual void UnlockAfterPeekExtantReleasedChunks() = 0;
#ifdef DEBUG
// DEBUG checks ensuring that this manager and its users avoid UAFs.
// Derived classes should assert that mUser is not null in their functions.
void RegisteredWith(const void* aUser) {
mUser = aUser;
void DeregisteredFrom(const void* aUser) {
MOZ_ASSERT(mUser == aUser);
mUser = nullptr;
const void* mUser = nullptr;
#endif // DEBUG
} // namespace mozilla
#endif // ProfileBufferChunkManager_h