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Diffstat (limited to 'mozglue/baseprofiler/public/ProfileChunkedBufferDetail.h')
| -rw-r--r-- | mozglue/baseprofiler/public/ProfileChunkedBufferDetail.h | 400 |
1 files changed, 400 insertions, 0 deletions
diff --git a/mozglue/baseprofiler/public/ProfileChunkedBufferDetail.h b/mozglue/baseprofiler/public/ProfileChunkedBufferDetail.h new file mode 100644 index 0000000000..9828822aaf --- /dev/null +++ b/mozglue/baseprofiler/public/ProfileChunkedBufferDetail.h @@ -0,0 +1,400 @@ +/* -*- 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 ProfileChunkedBufferDetail_h +#define ProfileChunkedBufferDetail_h + +#include "mozilla/Assertions.h" +#include "mozilla/Likely.h" +#include "mozilla/ProfileBufferChunk.h" +#include "mozilla/ProfileBufferEntrySerialization.h" + +namespace mozilla::profiler::detail { + +// Internal accessor pointing at a position inside a chunk. +// It can handle two groups of chunks (typically the extant chunks stored in +// the store manager, and the current chunk). +// The main operations are: +// - ReadEntrySize() to read an entry size, 0 means failure. +// - operator+=(Length) to skip a number of bytes. +// - EntryReader() creates an entry reader at the current position for a given +// size (it may fail with an empty reader), and skips the entry. +// Note that there is no "past-the-end" position -- as soon as InChunkPointer +// reaches the end, it becomes effectively null. +class InChunkPointer { + public: + using Byte = ProfileBufferChunk::Byte; + using Length = ProfileBufferChunk::Length; + + // Nullptr-like InChunkPointer, may be used as end iterator. + InChunkPointer() + : mChunk(nullptr), mNextChunkGroup(nullptr), mOffsetInChunk(0) {} + + // InChunkPointer over one or two chunk groups, pointing at the given + // block index (if still in range). + // This constructor should only be used with *trusted* block index values! + InChunkPointer(const ProfileBufferChunk* aChunk, + const ProfileBufferChunk* aNextChunkGroup, + ProfileBufferBlockIndex aBlockIndex) + : mChunk(aChunk), mNextChunkGroup(aNextChunkGroup) { + if (mChunk) { + mOffsetInChunk = mChunk->OffsetFirstBlock(); + Adjust(); + } else if (mNextChunkGroup) { + mChunk = mNextChunkGroup; + mNextChunkGroup = nullptr; + mOffsetInChunk = mChunk->OffsetFirstBlock(); + Adjust(); + } else { + mOffsetInChunk = 0; + } + + // Try to advance to given position. + if (!AdvanceToGlobalRangePosition(aBlockIndex)) { + // Block does not exist anymore (or block doesn't look valid), reset the + // in-chunk pointer. + mChunk = nullptr; + mNextChunkGroup = nullptr; + } + } + + // InChunkPointer over one or two chunk groups, will start at the first + // block (if any). This may be slow, so avoid using it too much. + InChunkPointer(const ProfileBufferChunk* aChunk, + const ProfileBufferChunk* aNextChunkGroup, + ProfileBufferIndex aIndex = ProfileBufferIndex(0)) + : mChunk(aChunk), mNextChunkGroup(aNextChunkGroup) { + if (mChunk) { + mOffsetInChunk = mChunk->OffsetFirstBlock(); + Adjust(); + } else if (mNextChunkGroup) { + mChunk = mNextChunkGroup; + mNextChunkGroup = nullptr; + mOffsetInChunk = mChunk->OffsetFirstBlock(); + Adjust(); + } else { + mOffsetInChunk = 0; + } + + // Try to advance to given position. + if (!AdvanceToGlobalRangePosition(aIndex)) { + // Block does not exist anymore, reset the in-chunk pointer. + mChunk = nullptr; + mNextChunkGroup = nullptr; + } + } + + // Compute the current position in the global range. + // 0 if null (including if we're reached the end). + [[nodiscard]] ProfileBufferIndex GlobalRangePosition() const { + if (IsNull()) { + return 0; + } + return mChunk->RangeStart() + mOffsetInChunk; + } + + // Move InChunkPointer forward to the block at the given global block + // position, which is assumed to be valid exactly -- but it may be obsolete. + // 0 stays where it is (if valid already). + // MOZ_ASSERTs if the index is invalid. + [[nodiscard]] bool AdvanceToGlobalRangePosition( + ProfileBufferBlockIndex aBlockIndex) { + if (IsNull()) { + // Pointer is null already. (Not asserting because it's acceptable.) + return false; + } + if (!aBlockIndex) { + // Special null position, just stay where we are. + return ShouldPointAtValidBlock(); + } + if (aBlockIndex.ConvertToProfileBufferIndex() < GlobalRangePosition()) { + // Past the requested position, stay where we are (assuming the current + // position was valid). + return ShouldPointAtValidBlock(); + } + for (;;) { + if (aBlockIndex.ConvertToProfileBufferIndex() < + mChunk->RangeStart() + mChunk->OffsetPastLastBlock()) { + // Target position is in this chunk's written space, move to it. + mOffsetInChunk = + aBlockIndex.ConvertToProfileBufferIndex() - mChunk->RangeStart(); + return ShouldPointAtValidBlock(); + } + // Position is after this chunk, try next chunk. + GoToNextChunk(); + if (IsNull()) { + return false; + } + // Skip whatever block tail there is, we don't allow pointing in the + // middle of a block. + mOffsetInChunk = mChunk->OffsetFirstBlock(); + if (aBlockIndex.ConvertToProfileBufferIndex() < GlobalRangePosition()) { + // Past the requested position, meaning that the given position was in- + // between blocks -> Failure. + MOZ_ASSERT(false, "AdvanceToGlobalRangePosition - In-between blocks"); + return false; + } + } + } + + // Move InChunkPointer forward to the block at or after the given global + // range position. + // 0 stays where it is (if valid already). + [[nodiscard]] bool AdvanceToGlobalRangePosition( + ProfileBufferIndex aPosition) { + if (aPosition == 0) { + // Special position '0', just stay where we are. + // Success if this position is already valid. + return !IsNull(); + } + for (;;) { + ProfileBufferIndex currentPosition = GlobalRangePosition(); + if (currentPosition == 0) { + // Pointer is null. + return false; + } + if (aPosition <= currentPosition) { + // At or past the requested position, stay where we are. + return true; + } + if (aPosition < mChunk->RangeStart() + mChunk->OffsetPastLastBlock()) { + // Target position is in this chunk's written space, move to it. + for (;;) { + // Skip the current block. + mOffsetInChunk += ReadEntrySize(); + if (mOffsetInChunk >= mChunk->OffsetPastLastBlock()) { + // Reached the end of the chunk, this can happen for the last + // block, let's just continue to the next chunk. + break; + } + if (aPosition <= mChunk->RangeStart() + mOffsetInChunk) { + // We're at or after the position, return at this block position. + return true; + } + } + } + // Position is after this chunk, try next chunk. + GoToNextChunk(); + if (IsNull()) { + return false; + } + // Skip whatever block tail there is, we don't allow pointing in the + // middle of a block. + mOffsetInChunk = mChunk->OffsetFirstBlock(); + } + } + + [[nodiscard]] Byte ReadByte() { + MOZ_ASSERT(!IsNull()); + MOZ_ASSERT(mOffsetInChunk < mChunk->OffsetPastLastBlock()); + Byte byte = mChunk->ByteAt(mOffsetInChunk); + if (MOZ_UNLIKELY(++mOffsetInChunk == mChunk->OffsetPastLastBlock())) { + Adjust(); + } + return byte; + } + + // Read and skip a ULEB128-encoded size. + // 0 means failure (0-byte entries are not allowed.) + // Note that this doesn't guarantee that there are actually that many bytes + // available to read! (EntryReader() below may gracefully fail.) + [[nodiscard]] Length ReadEntrySize() { + ULEB128Reader<Length> reader; + if (IsNull()) { + return 0; + } + for (;;) { + const bool isComplete = reader.FeedByteIsComplete(ReadByte()); + if (MOZ_UNLIKELY(IsNull())) { + // End of chunks, so there's no actual entry after this anyway. + return 0; + } + if (MOZ_LIKELY(isComplete)) { + if (MOZ_UNLIKELY(reader.Value() > mChunk->BufferBytes())) { + // Don't allow entries larger than a chunk. + return 0; + } + return reader.Value(); + } + } + } + + InChunkPointer& operator+=(Length aLength) { + MOZ_ASSERT(!IsNull()); + mOffsetInChunk += aLength; + Adjust(); + return *this; + } + + [[nodiscard]] ProfileBufferEntryReader EntryReader(Length aLength) { + if (IsNull() || aLength == 0) { + return ProfileBufferEntryReader(); + } + + MOZ_ASSERT(mOffsetInChunk < mChunk->OffsetPastLastBlock()); + + // We should be pointing at the entry, past the entry size. + const ProfileBufferIndex entryIndex = GlobalRangePosition(); + // Verify that there's enough space before for the size (starting at index + // 1 at least). + MOZ_ASSERT(entryIndex >= 1u + ULEB128Size(aLength)); + + const Length remaining = mChunk->OffsetPastLastBlock() - mOffsetInChunk; + Span<const Byte> mem0 = mChunk->BufferSpan(); + mem0 = mem0.From(mOffsetInChunk); + if (aLength <= remaining) { + // Move to the end of this block, which could make this null if we have + // reached the end of all buffers. + *this += aLength; + return ProfileBufferEntryReader( + mem0.To(aLength), + // Block starts before the entry size. + ProfileBufferBlockIndex::CreateFromProfileBufferIndex( + entryIndex - ULEB128Size(aLength)), + // Block ends right after the entry (could be null for last entry). + ProfileBufferBlockIndex::CreateFromProfileBufferIndex( + GlobalRangePosition())); + } + + // We need to go to the next chunk for the 2nd part of this block. + GoToNextChunk(); + if (IsNull()) { + return ProfileBufferEntryReader(); + } + + Span<const Byte> mem1 = mChunk->BufferSpan(); + const Length tail = aLength - remaining; + MOZ_ASSERT(tail <= mChunk->BufferBytes()); + MOZ_ASSERT(tail == mChunk->OffsetFirstBlock()); + // We are in the correct chunk, move the offset to the end of the block. + mOffsetInChunk = tail; + // And adjust as needed, which could make this null if we have reached the + // end of all buffers. + Adjust(); + return ProfileBufferEntryReader( + mem0, mem1.To(tail), + // Block starts before the entry size. + ProfileBufferBlockIndex::CreateFromProfileBufferIndex( + entryIndex - ULEB128Size(aLength)), + // Block ends right after the entry (could be null for last entry). + ProfileBufferBlockIndex::CreateFromProfileBufferIndex( + GlobalRangePosition())); + } + + [[nodiscard]] bool IsNull() const { return !mChunk; } + + [[nodiscard]] bool operator==(const InChunkPointer& aOther) const { + if (IsNull() || aOther.IsNull()) { + return IsNull() && aOther.IsNull(); + } + return mChunk == aOther.mChunk && mOffsetInChunk == aOther.mOffsetInChunk; + } + + [[nodiscard]] bool operator!=(const InChunkPointer& aOther) const { + return !(*this == aOther); + } + + [[nodiscard]] Byte operator*() const { + MOZ_ASSERT(!IsNull()); + MOZ_ASSERT(mOffsetInChunk < mChunk->OffsetPastLastBlock()); + return mChunk->ByteAt(mOffsetInChunk); + } + + InChunkPointer& operator++() { + MOZ_ASSERT(!IsNull()); + MOZ_ASSERT(mOffsetInChunk < mChunk->OffsetPastLastBlock()); + if (MOZ_UNLIKELY(++mOffsetInChunk == mChunk->OffsetPastLastBlock())) { + mOffsetInChunk = 0; + GoToNextChunk(); + Adjust(); + } + return *this; + } + + private: + void GoToNextChunk() { + MOZ_ASSERT(!IsNull()); + const ProfileBufferIndex expectedNextRangeStart = + mChunk->RangeStart() + mChunk->BufferBytes(); + + mChunk = mChunk->GetNext(); + if (!mChunk) { + // Reached the end of the current chunk group, try the next one (which + // may be null too, especially on the 2nd try). + mChunk = mNextChunkGroup; + mNextChunkGroup = nullptr; + } + + if (mChunk && mChunk->RangeStart() == 0) { + // Reached a chunk without a valid (non-null) range start, assume there + // are only unused chunks from here on. + mChunk = nullptr; + } + + MOZ_ASSERT(!mChunk || mChunk->RangeStart() == expectedNextRangeStart, + "We don't handle discontinuous buffers (yet)"); + // Non-DEBUG fallback: Stop reading past discontinuities. + // (They should be rare, only happening on temporary OOMs.) + // TODO: Handle discontinuities (by skipping over incomplete blocks). + if (mChunk && mChunk->RangeStart() != expectedNextRangeStart) { + mChunk = nullptr; + } + } + + // We want `InChunkPointer` to always point at a valid byte (or be null). + // After some operations, `mOffsetInChunk` may point past the end of the + // current `mChunk`, in which case we need to adjust our position to be inside + // the appropriate chunk. E.g., if we're 10 bytes after the end of the current + // chunk, we should end up at offset 10 in the next chunk. + // Note that we may "fall off" the last chunk and make this `InChunkPointer` + // effectively null. + void Adjust() { + while (mChunk && mOffsetInChunk >= mChunk->OffsetPastLastBlock()) { + // TODO: Try to adjust offset between chunks relative to mRangeStart + // differences. But we don't handle discontinuities yet. + if (mOffsetInChunk < mChunk->BufferBytes()) { + mOffsetInChunk -= mChunk->BufferBytes(); + } else { + mOffsetInChunk -= mChunk->OffsetPastLastBlock(); + } + GoToNextChunk(); + } + } + + // Check if the current position is likely to point at a valid block. + // (Size should be reasonable, and block should fully fit inside buffer.) + // MOZ_ASSERTs on failure, to catch incorrect uses of block indices (which + // should only point at valid blocks if still in range). Non-asserting build + // fallback should still be handled. + [[nodiscard]] bool ShouldPointAtValidBlock() const { + if (IsNull()) { + // Pointer is null, no blocks here. + MOZ_ASSERT(false, "ShouldPointAtValidBlock - null pointer"); + return false; + } + // Use a copy, so we don't modify `*this`. + InChunkPointer pointer = *this; + // Try to read the entry size. + Length entrySize = pointer.ReadEntrySize(); + if (entrySize == 0) { + // Entry size of zero means we read 0 or a way-too-big value. + MOZ_ASSERT(false, "ShouldPointAtValidBlock - invalid size"); + return false; + } + // See if the last byte of the entry is still inside the buffer. + pointer += entrySize - 1; + MOZ_ASSERT(!IsNull(), "ShouldPointAtValidBlock - past end of buffer"); + return !IsNull(); + } + + const ProfileBufferChunk* mChunk; + const ProfileBufferChunk* mNextChunkGroup; + Length mOffsetInChunk; +}; + +} // namespace mozilla::profiler::detail + +#endif // ProfileChunkedBufferDetail_h |