/* -*- Mode: C++; tab-width: 8; 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 mozilla_BufferList_h
#define mozilla_BufferList_h
#include <algorithm>
#include "mozilla/AllocPolicy.h"
#include "mozilla/Maybe.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Move.h"
#include "mozilla/ScopeExit.h"
#include "mozilla/Types.h"
#include "mozilla/TypeTraits.h"
#include "mozilla/Vector.h"
#include <string.h>
// BufferList represents a sequence of buffers of data. A BufferList can choose
// to own its buffers or not. The class handles writing to the buffers,
// iterating over them, and reading data out. Unlike SegmentedVector, the
// buffers may be of unequal size. Like SegmentedVector, BufferList is a nice
// way to avoid large contiguous allocations (which can trigger OOMs).
class InfallibleAllocPolicy;
namespace mozilla {
template <typename AllocPolicy>
class BufferList : private AllocPolicy {
// Each buffer in a BufferList has a size and a capacity. The first mSize
// bytes are initialized and the remaining |mCapacity - mSize| bytes are free.
struct Segment {
char* mData;
size_t mSize;
size_t mCapacity;
Segment(char* aData, size_t aSize, size_t aCapacity)
: mData(aData), mSize(aSize), mCapacity(aCapacity) {}
Segment(const Segment&) = delete;
Segment& operator=(const Segment&) = delete;
Segment(Segment&&) = default;
Segment& operator=(Segment&&) = default;
char* Start() const { return mData; }
char* End() const { return mData + mSize; }
};
template <typename OtherAllocPolicy>
friend class BufferList;
public:
// For the convenience of callers, all segments are required to be a multiple
// of 8 bytes in capacity. Also, every buffer except the last one is required
// to be full (i.e., size == capacity). Therefore, a byte at offset N within
// the BufferList and stored in memory at an address A will satisfy
// (N % Align == A % Align) if Align == 2, 4, or 8.
static const size_t kSegmentAlignment = 8;
// Allocate a BufferList. The BufferList will free all its buffers when it is
// destroyed. If an infallible allocator is used, an initial buffer of size
// aInitialSize and capacity aInitialCapacity is allocated automatically. This
// data will be contiguous and can be accessed via |Start()|. If a fallible
// alloc policy is used, aInitialSize must be 0, and the fallible |Init()|
// method may be called instead. Subsequent buffers will be allocated with
// capacity aStandardCapacity.
BufferList(size_t aInitialSize, size_t aInitialCapacity,
size_t aStandardCapacity, AllocPolicy aAP = AllocPolicy())
: AllocPolicy(aAP),
mOwning(true),
mSegments(aAP),
mSize(0),
mStandardCapacity(aStandardCapacity) {
MOZ_ASSERT(aInitialCapacity % kSegmentAlignment == 0);
MOZ_ASSERT(aStandardCapacity % kSegmentAlignment == 0);
if (aInitialCapacity) {
MOZ_ASSERT((aInitialSize == 0 ||
IsSame<AllocPolicy, InfallibleAllocPolicy>::value),
"BufferList may only be constructed with an initial size when "
"using an infallible alloc policy");
AllocateSegment(aInitialSize, aInitialCapacity);
}
}
BufferList(const BufferList& aOther) = delete;
BufferList(BufferList&& aOther)
: mOwning(aOther.mOwning),
mSegments(Move(aOther.mSegments)),
mSize(aOther.mSize),
mStandardCapacity(aOther.mStandardCapacity) {
aOther.mSegments.clear();
aOther.mSize = 0;
}
BufferList& operator=(const BufferList& aOther) = delete;
BufferList& operator=(BufferList&& aOther) {
Clear();
mOwning = aOther.mOwning;
mSegments = Move(aOther.mSegments);
mSize = aOther.mSize;
aOther.mSegments.clear();
aOther.mSize = 0;
return *this;
}
~BufferList() { Clear(); }
// Initializes the BufferList with a segment of the given size and capacity.
// May only be called once, before any segments have been allocated.
bool Init(size_t aInitialSize, size_t aInitialCapacity) {
MOZ_ASSERT(mSegments.empty());
MOZ_ASSERT(aInitialCapacity != 0);
MOZ_ASSERT(aInitialCapacity % kSegmentAlignment == 0);
return AllocateSegment(aInitialSize, aInitialCapacity);
}
// Returns the sum of the sizes of all the buffers.
size_t Size() const { return mSize; }
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
size_t size = mSegments.sizeOfExcludingThis(aMallocSizeOf);
for (Segment& segment : mSegments) {
size += aMallocSizeOf(segment.Start());
}
return size;
}
void Clear() {
if (mOwning) {
for (Segment& segment : mSegments) {
this->free_(segment.mData);
}
}
mSegments.clear();
mSize = 0;
}
// Iterates over bytes in the segments. You can advance it by as many bytes as
// you choose.
class IterImpl {
// Invariants:
// (0) mSegment <= bufferList.mSegments.length()
// (1) mData <= mDataEnd
// (2) If mSegment is not the last segment, mData < mDataEnd
uintptr_t mSegment;
char* mData;
char* mDataEnd;
friend class BufferList;
public:
explicit IterImpl(const BufferList& aBuffers)
: mSegment(0), mData(nullptr), mDataEnd(nullptr) {
if (!aBuffers.mSegments.empty()) {
mData = aBuffers.mSegments[0].Start();
mDataEnd = aBuffers.mSegments[0].End();
}
}
// Returns a pointer to the raw data. It is valid to access up to
// RemainingInSegment bytes of this buffer.
char* Data() const {
MOZ_RELEASE_ASSERT(!Done());
return mData;
}
// Returns true if the memory in the range [Data(), Data() + aBytes) is all
// part of one contiguous buffer.
bool HasRoomFor(size_t aBytes) const {
MOZ_RELEASE_ASSERT(mData <= mDataEnd);
return size_t(mDataEnd - mData) >= aBytes;
}
// Returns the maximum value aBytes for which HasRoomFor(aBytes) will be
// true.
size_t RemainingInSegment() const {
MOZ_RELEASE_ASSERT(mData <= mDataEnd);
return mDataEnd - mData;
}
// Advances the iterator by aBytes bytes. aBytes must be less than
// RemainingInSegment(). If advancing by aBytes takes the iterator to the
// end of a buffer, it will be moved to the beginning of the next buffer
// unless it is the last buffer.
void Advance(const BufferList& aBuffers, size_t aBytes) {
const Segment& segment = aBuffers.mSegments[mSegment];
MOZ_RELEASE_ASSERT(segment.Start() <= mData);
MOZ_RELEASE_ASSERT(mData <= mDataEnd);
MOZ_RELEASE_ASSERT(mDataEnd == segment.End());
MOZ_RELEASE_ASSERT(HasRoomFor(aBytes));
mData += aBytes;
if (mData == mDataEnd && mSegment + 1 < aBuffers.mSegments.length()) {
mSegment++;
const Segment& nextSegment = aBuffers.mSegments[mSegment];
mData = nextSegment.Start();
mDataEnd = nextSegment.End();
MOZ_RELEASE_ASSERT(mData < mDataEnd);
}
}
// Advance the iterator by aBytes, possibly crossing segments. This function
// returns false if it runs out of buffers to advance through. Otherwise it
// returns true.
bool AdvanceAcrossSegments(const BufferList& aBuffers, size_t aBytes) {
size_t bytes = aBytes;
while (bytes) {
size_t toAdvance = std::min(bytes, RemainingInSegment());
if (!toAdvance) {
return false;
}
Advance(aBuffers, toAdvance);
bytes -= toAdvance;
}
return true;
}
// Returns true when the iterator reaches the end of the BufferList.
bool Done() const { return mData == mDataEnd; }
private:
// Count the bytes we would need to advance in order to reach aTarget.
size_t BytesUntil(const BufferList& aBuffers,
const IterImpl& aTarget) const {
size_t offset = 0;
MOZ_ASSERT(aTarget.IsIn(aBuffers));
char* data = mData;
for (uintptr_t segment = mSegment; segment < aTarget.mSegment;
segment++) {
offset += aBuffers.mSegments[segment].End() - data;
data = aBuffers.mSegments[segment].mData;
}
MOZ_RELEASE_ASSERT(IsIn(aBuffers));
MOZ_RELEASE_ASSERT(aTarget.mData >= data);
offset += aTarget.mData - data;
return offset;
}
bool IsIn(const BufferList& aBuffers) const {
return mSegment < aBuffers.mSegments.length() &&
mData >= aBuffers.mSegments[mSegment].mData &&
mData < aBuffers.mSegments[mSegment].End();
}
};
// Special convenience method that returns Iter().Data().
char* Start() {
MOZ_RELEASE_ASSERT(!mSegments.empty());
return mSegments[0].mData;
}
const char* Start() const { return mSegments[0].mData; }
IterImpl Iter() const { return IterImpl(*this); }
// Copies aSize bytes from aData into the BufferList. The storage for these
// bytes may be split across multiple buffers. Size() is increased by aSize.
inline bool WriteBytes(const char* aData, size_t aSize);
// Allocates a buffer of at most |aMaxBytes| bytes and, if successful, returns
// that buffer, and places its size in |aSize|. If unsuccessful, returns null
// and leaves |aSize| undefined.
inline char* AllocateBytes(size_t aMaxSize, size_t* aSize);
// Copies possibly non-contiguous byte range starting at aIter into
// aData. aIter is advanced by aSize bytes. Returns false if it runs out of
// data before aSize.
inline bool ReadBytes(IterImpl& aIter, char* aData, size_t aSize) const;
// Return a new BufferList that shares storage with this BufferList. The new
// BufferList is read-only. It allows iteration over aSize bytes starting at
// aIter. Borrow can fail, in which case *aSuccess will be false upon
// return. The borrowed BufferList can use a different AllocPolicy than the
// original one. However, it is not responsible for freeing buffers, so the
// AllocPolicy is only used for the buffer vector.
template <typename BorrowingAllocPolicy>
BufferList<BorrowingAllocPolicy> Borrow(
IterImpl& aIter, size_t aSize, bool* aSuccess,
BorrowingAllocPolicy aAP = BorrowingAllocPolicy()) const;
// Return a new BufferList and move storage from this BufferList to it. The
// new BufferList owns the buffers. Move can fail, in which case *aSuccess
// will be false upon return. The new BufferList can use a different
// AllocPolicy than the original one. The new OtherAllocPolicy is responsible
// for freeing buffers, so the OtherAllocPolicy must use freeing method
// compatible to the original one.
template <typename OtherAllocPolicy>
BufferList<OtherAllocPolicy> MoveFallible(
bool* aSuccess, OtherAllocPolicy aAP = OtherAllocPolicy());
// Return a new BufferList that adopts the byte range starting at Iter so that
// range [aIter, aIter + aSize) is transplanted to the returned BufferList.
// Contents of the buffer before aIter + aSize is left undefined.
// Extract can fail, in which case *aSuccess will be false upon return. The
// moved buffers are erased from the original BufferList. In case of extract
// fails, the original BufferList is intact. All other iterators except aIter
// are invalidated.
// This method requires aIter and aSize to be 8-byte aligned.
BufferList Extract(IterImpl& aIter, size_t aSize, bool* aSuccess);
// Return the number of bytes from 'start' to 'end', two iterators within
// this BufferList.
size_t RangeLength(const IterImpl& start, const IterImpl& end) const {
MOZ_ASSERT(start.IsIn(*this) && end.IsIn(*this));
return start.BytesUntil(*this, end);
}
// This takes ownership of the data
void* WriteBytesZeroCopy(char* aData, size_t aSize, size_t aCapacity) {
MOZ_ASSERT(aCapacity != 0);
MOZ_ASSERT(aSize <= aCapacity);
MOZ_ASSERT(mOwning);
if (!mSegments.append(Segment(aData, aSize, aCapacity))) {
this->free_(aData);
return nullptr;
}
mSize += aSize;
return aData;
}
private:
explicit BufferList(AllocPolicy aAP)
: AllocPolicy(aAP), mOwning(false), mSize(0), mStandardCapacity(0) {}
char* AllocateSegment(size_t aSize, size_t aCapacity) {
MOZ_RELEASE_ASSERT(mOwning);
MOZ_ASSERT(aCapacity != 0);
MOZ_ASSERT(aSize <= aCapacity);
char* data = this->template pod_malloc<char>(aCapacity);
if (!data) {
return nullptr;
}
if (!mSegments.append(Segment(data, aSize, aCapacity))) {
this->free_(data);
return nullptr;
}
mSize += aSize;
return data;
}
bool mOwning;
Vector<Segment, 1, AllocPolicy> mSegments;
size_t mSize;
size_t mStandardCapacity;
};
template <typename AllocPolicy>
bool BufferList<AllocPolicy>::WriteBytes(const char* aData, size_t aSize) {
MOZ_RELEASE_ASSERT(mOwning);
MOZ_RELEASE_ASSERT(mStandardCapacity);
size_t copied = 0;
while (copied < aSize) {
size_t toCopy;
char* data = AllocateBytes(aSize - copied, &toCopy);
if (!data) {
return false;
}
memcpy(data, aData + copied, toCopy);
copied += toCopy;
}
return true;
}
template <typename AllocPolicy>
char* BufferList<AllocPolicy>::AllocateBytes(size_t aMaxSize, size_t* aSize) {
MOZ_RELEASE_ASSERT(mOwning);
MOZ_RELEASE_ASSERT(mStandardCapacity);
if (!mSegments.empty()) {
Segment& lastSegment = mSegments.back();
size_t capacity = lastSegment.mCapacity - lastSegment.mSize;
if (capacity) {
size_t size = std::min(aMaxSize, capacity);
char* data = lastSegment.mData + lastSegment.mSize;
lastSegment.mSize += size;
mSize += size;
*aSize = size;
return data;
}
}
size_t size = std::min(aMaxSize, mStandardCapacity);
char* data = AllocateSegment(size, mStandardCapacity);
if (data) {
*aSize = size;
}
return data;
}
template <typename AllocPolicy>
bool BufferList<AllocPolicy>::ReadBytes(IterImpl& aIter, char* aData,
size_t aSize) const {
size_t copied = 0;
size_t remaining = aSize;
while (remaining) {
size_t toCopy = std::min(aIter.RemainingInSegment(), remaining);
if (!toCopy) {
// We've run out of data in the last segment.
return false;
}
memcpy(aData + copied, aIter.Data(), toCopy);
copied += toCopy;
remaining -= toCopy;
aIter.Advance(*this, toCopy);
}
return true;
}
template <typename AllocPolicy>
template <typename BorrowingAllocPolicy>
BufferList<BorrowingAllocPolicy> BufferList<AllocPolicy>::Borrow(
IterImpl& aIter, size_t aSize, bool* aSuccess,
BorrowingAllocPolicy aAP) const {
BufferList<BorrowingAllocPolicy> result(aAP);
size_t size = aSize;
while (size) {
size_t toAdvance = std::min(size, aIter.RemainingInSegment());
if (!toAdvance || !result.mSegments.append(
typename BufferList<BorrowingAllocPolicy>::Segment(
aIter.mData, toAdvance, toAdvance))) {
*aSuccess = false;
return result;
}
aIter.Advance(*this, toAdvance);
size -= toAdvance;
}
result.mSize = aSize;
*aSuccess = true;
return result;
}
template <typename AllocPolicy>
template <typename OtherAllocPolicy>
BufferList<OtherAllocPolicy> BufferList<AllocPolicy>::MoveFallible(
bool* aSuccess, OtherAllocPolicy aAP) {
BufferList<OtherAllocPolicy> result(0, 0, mStandardCapacity, aAP);
IterImpl iter = Iter();
while (!iter.Done()) {
size_t toAdvance = iter.RemainingInSegment();
if (!toAdvance ||
!result.mSegments.append(typename BufferList<OtherAllocPolicy>::Segment(
iter.mData, toAdvance, toAdvance))) {
*aSuccess = false;
result.mSegments.clear();
return result;
}
iter.Advance(*this, toAdvance);
}
result.mSize = mSize;
mSegments.clear();
mSize = 0;
*aSuccess = true;
return result;
}
template <typename AllocPolicy>
BufferList<AllocPolicy> BufferList<AllocPolicy>::Extract(IterImpl& aIter,
size_t aSize,
bool* aSuccess) {
MOZ_RELEASE_ASSERT(aSize);
MOZ_RELEASE_ASSERT(mOwning);
MOZ_ASSERT(aSize % kSegmentAlignment == 0);
MOZ_ASSERT(intptr_t(aIter.mData) % kSegmentAlignment == 0);
auto failure = [this, aSuccess]() {
*aSuccess = false;
return BufferList(0, 0, mStandardCapacity);
};
// Number of segments we'll need to copy data from to satisfy the request.
size_t segmentsNeeded = 0;
// If this is None then the last segment is a full segment, otherwise we need
// to copy this many bytes.
Maybe<size_t> lastSegmentSize;
{
// Copy of the iterator to walk the BufferList and see how many segments we
// need to copy.
IterImpl iter = aIter;
size_t remaining = aSize;
while (!iter.Done() && remaining &&
remaining >= iter.RemainingInSegment()) {
remaining -= iter.RemainingInSegment();
iter.Advance(*this, iter.RemainingInSegment());
segmentsNeeded++;
}
if (remaining) {
if (iter.Done()) {
// We reached the end of the BufferList and there wasn't enough data to
// satisfy the request.
return failure();
}
lastSegmentSize.emplace(remaining);
// The last block also counts as a segment. This makes the conditionals
// on segmentsNeeded work in the rest of the function.
segmentsNeeded++;
}
}
BufferList result(0, 0, mStandardCapacity);
if (!result.mSegments.reserve(segmentsNeeded + lastSegmentSize.isSome())) {
return failure();
}
// Copy the first segment, it's special because we can't just steal the
// entire Segment struct from this->mSegments.
size_t firstSegmentSize = std::min(aSize, aIter.RemainingInSegment());
if (!result.WriteBytes(aIter.Data(), firstSegmentSize)) {
return failure();
}
aIter.Advance(*this, firstSegmentSize);
segmentsNeeded--;
// The entirety of the request wasn't in the first segment, now copy the
// rest.
if (segmentsNeeded) {
char* finalSegment = nullptr;
// Pre-allocate the final segment so that if this fails, we return before
// we delete the elements from |this->mSegments|.
if (lastSegmentSize.isSome()) {
MOZ_RELEASE_ASSERT(mStandardCapacity >= *lastSegmentSize);
finalSegment = this->template pod_malloc<char>(mStandardCapacity);
if (!finalSegment) {
return failure();
}
}
size_t copyStart = aIter.mSegment;
// Copy segments from this over to the result and remove them from our
// storage. Not needed if the only segment we need to copy is the last
// partial one.
size_t segmentsToCopy = segmentsNeeded - lastSegmentSize.isSome();
for (size_t i = 0; i < segmentsToCopy; ++i) {
result.mSegments.infallibleAppend(Segment(
mSegments[aIter.mSegment].mData, mSegments[aIter.mSegment].mSize,
mSegments[aIter.mSegment].mCapacity));
aIter.Advance(*this, aIter.RemainingInSegment());
}
// Due to the way IterImpl works, there are two cases here: (1) if we've
// consumed the entirety of the BufferList, then the iterator is pointed at
// the end of the final segment, (2) otherwise it is pointed at the start
// of the next segment. We want to verify that we really consumed all
// |segmentsToCopy| segments.
MOZ_RELEASE_ASSERT(
(aIter.mSegment == copyStart + segmentsToCopy) ||
(aIter.Done() && aIter.mSegment == copyStart + segmentsToCopy - 1));
mSegments.erase(mSegments.begin() + copyStart,
mSegments.begin() + copyStart + segmentsToCopy);
// Reset the iter's position for what we just deleted.
aIter.mSegment -= segmentsToCopy;
if (lastSegmentSize.isSome()) {
// We called reserve() on result.mSegments so infallibleAppend is safe.
result.mSegments.infallibleAppend(
Segment(finalSegment, 0, mStandardCapacity));
bool r = result.WriteBytes(aIter.Data(), *lastSegmentSize);
MOZ_RELEASE_ASSERT(r);
aIter.Advance(*this, *lastSegmentSize);
}
}
mSize -= aSize;
result.mSize = aSize;
*aSuccess = true;
return result;
}
} // namespace mozilla
#endif /* mozilla_BufferList_h */