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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 http://mozilla.org/MPL/2.0/. */
+
+#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 {
+ public:
+ 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) {
+ mInitialChunk->MarkRecycled();
+ 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.
+ std::move(aChunkReceiver)(GetChunk());
+ }
+
+ void FulfillChunkRequests() final {
+ // Nothing to do here.
+ }
+
+ void ReleaseChunk(UniquePtr<ProfileBufferChunk> aChunk) final {
+ MOZ_ASSERT(mUser, "Not registered yet");
+ if (!aChunk) {
+ return;
+ }
+ 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);
+ }
+
+ protected:
+ // 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));
+ }
+
+ private:
+ // 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