The Tor Browser: comparison xpcom/glue/nsTArray-inl.h

--1:000000000000
+:3a18f5da469f
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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 nsTArray_h__
+#  error "Don't include this file directly"
+#endif
+template<class Alloc, class Copy>
+nsTArray_base<Alloc, Copy>::nsTArray_base()
+: mHdr(EmptyHdr()) {
+MOZ_COUNT_CTOR(nsTArray_base);
+}
+template<class Alloc, class Copy>
+nsTArray_base<Alloc, Copy>::~nsTArray_base() {
+if (mHdr != EmptyHdr() && !UsesAutoArrayBuffer()) {
+Alloc::Free(mHdr);
+}
+MOZ_COUNT_DTOR(nsTArray_base);
+}
+template<class Alloc, class Copy>
+const nsTArrayHeader* nsTArray_base<Alloc, Copy>::GetAutoArrayBufferUnsafe(size_t elemAlign) const {
+// Assuming |this| points to an nsAutoArray, we want to get a pointer to
+// mAutoBuf.  So just cast |this| to nsAutoArray* and read &mAutoBuf!
+const void* autoBuf = &reinterpret_cast<const nsAutoArrayBase<nsTArray<uint32_t>, 1>*>(this)->mAutoBuf;
+// If we're on a 32-bit system and elemAlign is 8, we need to adjust our
+// pointer to take into account the extra alignment in the auto array.
+static_assert(sizeof(void*) != 4 ||
+(MOZ_ALIGNOF(mozilla::AlignedElem<8>) == 8 &&
+sizeof(nsAutoTArray<mozilla::AlignedElem<8>, 1>) ==
+sizeof(void*) + sizeof(nsTArrayHeader) +
+4 + sizeof(mozilla::AlignedElem<8>)),
+"auto array padding wasn't what we expected");
+// We don't support alignments greater than 8 bytes.
+NS_ABORT_IF_FALSE(elemAlign <= 4 || elemAlign == 8, "unsupported alignment.");
+if (sizeof(void*) == 4 && elemAlign == 8) {
+autoBuf = reinterpret_cast<const char*>(autoBuf) + 4;
+}
+return reinterpret_cast<const Header*>(autoBuf);
+}
+template<class Alloc, class Copy>
+bool nsTArray_base<Alloc, Copy>::UsesAutoArrayBuffer() const {
+if (!mHdr->mIsAutoArray) {
+return false;
+}
+// This is nuts.  If we were sane, we'd pass elemAlign as a parameter to
+// this function.  Unfortunately this function is called in nsTArray_base's
+// destructor, at which point we don't know elem_type's alignment.
+//
+// We'll fall on our face and return true when we should say false if
+//
+//   * we're not using our auto buffer,
+//   * elemAlign == 4, and
+//   * mHdr == GetAutoArrayBuffer(8).
+//
+// This could happen if |*this| lives on the heap and malloc allocated our
+// buffer on the heap adjacent to |*this|.
+//
+// However, we can show that this can't happen.  If |this| is an auto array
+// (as we ensured at the beginning of the method), GetAutoArrayBuffer(8)
+// always points to memory owned by |*this|, because (as we assert below)
+//
+//   * GetAutoArrayBuffer(8) is at most 4 bytes past GetAutoArrayBuffer(4), and
+//   * sizeof(nsTArrayHeader) > 4.
+//
+// Since nsAutoTArray always contains an nsTArrayHeader,
+// GetAutoArrayBuffer(8) will always point inside the auto array object,
+// even if it doesn't point at the beginning of the header.
+//
+// Note that this means that we can't store elements with alignment 16 in an
+// nsTArray, because GetAutoArrayBuffer(16) could lie outside the memory
+// owned by this nsAutoTArray.  We statically assert that elem_type's
+// alignment is 8 bytes or less in nsAutoArrayBase.
+static_assert(sizeof(nsTArrayHeader) > 4,
+"see comment above");
+#ifdef DEBUG
+ptrdiff_t diff = reinterpret_cast<const char*>(GetAutoArrayBuffer(8)) -
+reinterpret_cast<const char*>(GetAutoArrayBuffer(4));
+NS_ABORT_IF_FALSE(diff >= 0 && diff <= 4, "GetAutoArrayBuffer doesn't do what we expect.");
+#endif
+return mHdr == GetAutoArrayBuffer(4) || mHdr == GetAutoArrayBuffer(8);
+}
+template<class Alloc, class Copy>
+typename Alloc::ResultTypeProxy
+nsTArray_base<Alloc, Copy>::EnsureCapacity(size_type capacity, size_type elemSize) {
+// This should be the most common case so test this first
+if (capacity <= mHdr->mCapacity)
+return Alloc::SuccessResult();
+// If the requested memory allocation exceeds size_type(-1)/2, then
+// our doubling algorithm may not be able to allocate it.
+// Additionally we couldn't fit in the Header::mCapacity
+// member. Just bail out in cases like that.  We don't want to be
+// allocating 2 GB+ arrays anyway.
+if ((uint64_t)capacity * elemSize > size_type(-1)/2) {
+Alloc::SizeTooBig((size_t)capacity * elemSize);
+return Alloc::FailureResult();
+}
+if (mHdr == EmptyHdr()) {
+// Malloc() new data
+Header *header = static_cast<Header*>
+(Alloc::Malloc(sizeof(Header) + capacity * elemSize));
+if (!header)
+return Alloc::FailureResult();
+header->mLength = 0;
+header->mCapacity = capacity;
+header->mIsAutoArray = 0;
+mHdr = header;
+return Alloc::SuccessResult();
+}
+// We increase our capacity so |capacity * elemSize + sizeof(Header)| is the
+// next power of two, if this value is less than pageSize bytes, or otherwise
+// so it's the next multiple of pageSize.
+const uint32_t pageSizeBytes = 12;
+const uint32_t pageSize = 1 << pageSizeBytes;
+uint32_t minBytes = capacity * elemSize + sizeof(Header);
+uint32_t bytesToAlloc;
+if (minBytes >= pageSize) {
+// Round up to the next multiple of pageSize.
+bytesToAlloc = pageSize * ((minBytes + pageSize - 1) / pageSize);
+}
+else {
+// Round up to the next power of two.  See
+// http://graphics.stanford.edu/~seander/bithacks.html
+bytesToAlloc = minBytes - 1;
+bytesToAlloc |= bytesToAlloc >> 1;
+bytesToAlloc |= bytesToAlloc >> 2;
+bytesToAlloc |= bytesToAlloc >> 4;
+bytesToAlloc |= bytesToAlloc >> 8;
+bytesToAlloc |= bytesToAlloc >> 16;
+bytesToAlloc++;
+MOZ_ASSERT((bytesToAlloc & (bytesToAlloc - 1)) == 0,
+"nsTArray's allocation size should be a power of two!");
+}
+Header *header;
+if (UsesAutoArrayBuffer() || !Copy::allowRealloc) {
+// Malloc() and copy
+header = static_cast<Header*>(Alloc::Malloc(bytesToAlloc));
+if (!header)
+return Alloc::FailureResult();
+Copy::CopyHeaderAndElements(header, mHdr, Length(), elemSize);
+if (!UsesAutoArrayBuffer())
+Alloc::Free(mHdr);
+} else {
+// Realloc() existing data
+header = static_cast<Header*>(Alloc::Realloc(mHdr, bytesToAlloc));
+if (!header)
+return Alloc::FailureResult();
+}
+// How many elements can we fit in bytesToAlloc?
+uint32_t newCapacity = (bytesToAlloc - sizeof(Header)) / elemSize;
+MOZ_ASSERT(newCapacity >= capacity, "Didn't enlarge the array enough!");
+header->mCapacity = newCapacity;
+mHdr = header;
+return Alloc::SuccessResult();
+}
+template<class Alloc, class Copy>
+void
+nsTArray_base<Alloc, Copy>::ShrinkCapacity(size_type elemSize, size_t elemAlign) {
+if (mHdr == EmptyHdr() || UsesAutoArrayBuffer())
+return;
+if (mHdr->mLength >= mHdr->mCapacity)  // should never be greater than...
+return;
+size_type length = Length();
+if (IsAutoArray() && GetAutoArrayBuffer(elemAlign)->mCapacity >= length) {
+Header* header = GetAutoArrayBuffer(elemAlign);
+// Copy data, but don't copy the header to avoid overwriting mCapacity
+header->mLength = length;
+Copy::CopyElements(header + 1, mHdr + 1, length, elemSize);
+Alloc::Free(mHdr);
+mHdr = header;
+return;
+}
+if (length == 0) {
+MOZ_ASSERT(!IsAutoArray(), "autoarray should have fit 0 elements");
+Alloc::Free(mHdr);
+mHdr = EmptyHdr();
+return;
+}
+size_type size = sizeof(Header) + length * elemSize;
+void *ptr = Alloc::Realloc(mHdr, size);
+if (!ptr)
+return;
+mHdr = static_cast<Header*>(ptr);
+mHdr->mCapacity = length;
+}
+template<class Alloc, class Copy>
+void
+nsTArray_base<Alloc, Copy>::ShiftData(index_type start,
+size_type oldLen, size_type newLen,
+size_type elemSize, size_t elemAlign) {
+if (oldLen == newLen)
+return;
+// Determine how many elements need to be shifted
+size_type num = mHdr->mLength - (start + oldLen);
+// Compute the resulting length of the array
+mHdr->mLength += newLen - oldLen;
+if (mHdr->mLength == 0) {
+ShrinkCapacity(elemSize, elemAlign);
+} else {
+// Maybe nothing needs to be shifted
+if (num == 0)
+return;
+// Perform shift (change units to bytes first)
+start *= elemSize;
+newLen *= elemSize;
+oldLen *= elemSize;
+char *base = reinterpret_cast<char*>(mHdr + 1) + start;
+Copy::MoveElements(base + newLen, base + oldLen, num, elemSize);
+}
+}
+template<class Alloc, class Copy>
+bool
+nsTArray_base<Alloc, Copy>::InsertSlotsAt(index_type index, size_type count,
+size_type elementSize, size_t elemAlign)  {
+MOZ_ASSERT(index <= Length(), "Bogus insertion index");
+size_type newLen = Length() + count;
+EnsureCapacity(newLen, elementSize);
+// Check for out of memory conditions
+if (Capacity() < newLen)
+return false;
+// Move the existing elements as needed.  Note that this will
+// change our mLength, so no need to call IncrementLength.
+ShiftData(index, 0, count, elementSize, elemAlign);
+return true;
+}
+// nsTArray_base::IsAutoArrayRestorer is an RAII class which takes
+// |nsTArray_base &array| in its constructor.  When it's destructed, it ensures
+// that
+//
+//   * array.mIsAutoArray has the same value as it did when we started, and
+//   * if array has an auto buffer and mHdr would otherwise point to sEmptyHdr,
+//     array.mHdr points to array's auto buffer.
+template<class Alloc, class Copy>
+nsTArray_base<Alloc, Copy>::IsAutoArrayRestorer::IsAutoArrayRestorer(
+nsTArray_base<Alloc, Copy> &array,
+size_t elemAlign)
+: mArray(array),
+mElemAlign(elemAlign),
+mIsAuto(array.IsAutoArray())
+{
+}
+template<class Alloc, class Copy>
+nsTArray_base<Alloc, Copy>::IsAutoArrayRestorer::~IsAutoArrayRestorer() {
+// Careful: We don't want to set mIsAutoArray = 1 on sEmptyHdr.
+if (mIsAuto && mArray.mHdr == mArray.EmptyHdr()) {
+// Call GetAutoArrayBufferUnsafe() because GetAutoArrayBuffer() asserts
+// that mHdr->mIsAutoArray is true, which surely isn't the case here.
+mArray.mHdr = mArray.GetAutoArrayBufferUnsafe(mElemAlign);
+mArray.mHdr->mLength = 0;
+}
+else if (mArray.mHdr != mArray.EmptyHdr()) {
+mArray.mHdr->mIsAutoArray = mIsAuto;
+}
+}
+template<class Alloc, class Copy>
+template<class Allocator>
+typename Alloc::ResultTypeProxy
+nsTArray_base<Alloc, Copy>::SwapArrayElements(nsTArray_base<Allocator, Copy>& other,
+size_type elemSize, size_t elemAlign) {
+// EnsureNotUsingAutoArrayBuffer will set mHdr = sEmptyHdr even if we have an
+// auto buffer.  We need to point mHdr back to our auto buffer before we
+// return, otherwise we'll forget that we have an auto buffer at all!
+// IsAutoArrayRestorer takes care of this for us.
+IsAutoArrayRestorer ourAutoRestorer(*this, elemAlign);
+typename nsTArray_base<Allocator, Copy>::IsAutoArrayRestorer otherAutoRestorer(other, elemAlign);
+// If neither array uses an auto buffer which is big enough to store the
+// other array's elements, then ensure that both arrays use malloc'ed storage
+// and swap their mHdr pointers.
+if ((!UsesAutoArrayBuffer() || Capacity() < other.Length()) &&
+(!other.UsesAutoArrayBuffer() || other.Capacity() < Length())) {
+if (!EnsureNotUsingAutoArrayBuffer(elemSize) ||
+!other.EnsureNotUsingAutoArrayBuffer(elemSize)) {
+return Alloc::FailureResult();
+}
+Header *temp = mHdr;
+mHdr = other.mHdr;
+other.mHdr = temp;
+return Alloc::SuccessResult();
+}
+// Swap the two arrays by copying, since at least one is using an auto
+// buffer which is large enough to hold all of the other's elements.  We'll
+// copy the shorter array into temporary storage.
+//
+// (We could do better than this in some circumstances.  Suppose we're
+// swapping arrays X and Y.  X has space for 2 elements in its auto buffer,
+// but currently has length 4, so it's using malloc'ed storage.  Y has length
+// 2.  When we swap X and Y, we don't need to use a temporary buffer; we can
+// write Y straight into X's auto buffer, write X's malloc'ed buffer on top
+// of Y, and then switch X to using its auto buffer.)
+if (!Alloc::Successful(EnsureCapacity(other.Length(), elemSize)) ||
+!Allocator::Successful(other.EnsureCapacity(Length(), elemSize))) {
+return Alloc::FailureResult();
+}
+// The EnsureCapacity calls above shouldn't have caused *both* arrays to
+// switch from their auto buffers to malloc'ed space.
+NS_ABORT_IF_FALSE(UsesAutoArrayBuffer() ||
+other.UsesAutoArrayBuffer(),
+"One of the arrays should be using its auto buffer.");
+size_type smallerLength = XPCOM_MIN(Length(), other.Length());
+size_type largerLength = XPCOM_MAX(Length(), other.Length());
+void *smallerElements, *largerElements;
+if (Length() <= other.Length()) {
+smallerElements = Hdr() + 1;
+largerElements = other.Hdr() + 1;
+}
+else {
+smallerElements = other.Hdr() + 1;
+largerElements = Hdr() + 1;
+}
+// Allocate temporary storage for the smaller of the two arrays.  We want to
+// allocate this space on the stack, if it's not too large.  Sounds like a
+// job for AutoTArray!  (One of the two arrays we're swapping is using an
+// auto buffer, so we're likely not allocating a lot of space here.  But one
+// could, in theory, allocate a huge AutoTArray on the heap.)
+nsAutoArrayBase<nsTArray_Impl<uint8_t, Alloc>, 64> temp;
+if (!Alloc::Successful(temp.EnsureCapacity(smallerLength, elemSize))) {
+return Alloc::FailureResult();
+}
+Copy::CopyElements(temp.Elements(), smallerElements, smallerLength, elemSize);
+Copy::CopyElements(smallerElements, largerElements, largerLength, elemSize);
+Copy::CopyElements(largerElements, temp.Elements(), smallerLength, elemSize);
+// Swap the arrays' lengths.
+NS_ABORT_IF_FALSE((other.Length() == 0 || mHdr != EmptyHdr()) &&
+(Length() == 0 || other.mHdr != EmptyHdr()),
+"Don't set sEmptyHdr's length.");
+size_type tempLength = Length();
+mHdr->mLength = other.Length();
+other.mHdr->mLength = tempLength;
+return Alloc::SuccessResult();
+}
+template<class Alloc, class Copy>
+bool
+nsTArray_base<Alloc, Copy>::EnsureNotUsingAutoArrayBuffer(size_type elemSize) {
+if (UsesAutoArrayBuffer()) {
+// If you call this on a 0-length array, we'll set that array's mHdr to
+// sEmptyHdr, in flagrant violation of the nsAutoTArray invariants.  It's
+// up to you to set it back!  (If you don't, the nsAutoTArray will forget
+// that it has an auto buffer.)
+if (Length() == 0) {
+mHdr = EmptyHdr();
+return true;
+}
+size_type size = sizeof(Header) + Length() * elemSize;
+Header* header = static_cast<Header*>(Alloc::Malloc(size));
+if (!header)
+return false;
+Copy::CopyHeaderAndElements(header, mHdr, Length(), elemSize);
+header->mCapacity = Length();
+mHdr = header;
+}
+return true;
+}

The Tor Browser / file comparison

comparison: xpcom/glue/nsTArray-inl.h

xpcom/glue/nsTArray-inl.h