mirror of
https://github.com/classilla/tenfourfox.git
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464 lines
16 KiB
C++
464 lines
16 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef nsTArray_h__
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# error "Don't include this file directly"
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#endif
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template<class Alloc, class Copy>
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nsTArray_base<Alloc, Copy>::nsTArray_base()
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: mHdr(EmptyHdr())
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{
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MOZ_COUNT_CTOR(nsTArray_base);
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}
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template<class Alloc, class Copy>
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nsTArray_base<Alloc, Copy>::~nsTArray_base()
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{
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if (mHdr != EmptyHdr() && !UsesAutoArrayBuffer()) {
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Alloc::Free(mHdr);
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}
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MOZ_COUNT_DTOR(nsTArray_base);
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}
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template<class Alloc, class Copy>
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const nsTArrayHeader*
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nsTArray_base<Alloc, Copy>::GetAutoArrayBufferUnsafe(size_t aElemAlign) const
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{
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// Assuming |this| points to an nsAutoArray, we want to get a pointer to
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// mAutoBuf. So just cast |this| to nsAutoArray* and read &mAutoBuf!
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const void* autoBuf =
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&reinterpret_cast<const nsAutoArrayBase<nsTArray<uint32_t>, 1>*>(this)->mAutoBuf;
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// If we're on a 32-bit system and aElemAlign is 8, we need to adjust our
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// pointer to take into account the extra alignment in the auto array.
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static_assert(sizeof(void*) != 4 ||
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(MOZ_ALIGNOF(mozilla::AlignedElem<8>) == 8 &&
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sizeof(nsAutoTArray<mozilla::AlignedElem<8>, 1>) ==
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sizeof(void*) + sizeof(nsTArrayHeader) +
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4 + sizeof(mozilla::AlignedElem<8>)),
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"auto array padding wasn't what we expected");
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// We don't support alignments greater than 8 bytes.
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MOZ_ASSERT(aElemAlign <= 4 || aElemAlign == 8,
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"unsupported alignment.");
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if (sizeof(void*) == 4 && aElemAlign == 8) {
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autoBuf = reinterpret_cast<const char*>(autoBuf) + 4;
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}
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return reinterpret_cast<const Header*>(autoBuf);
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}
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template<class Alloc, class Copy>
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bool
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nsTArray_base<Alloc, Copy>::UsesAutoArrayBuffer() const
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{
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if (!mHdr->mIsAutoArray) {
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return false;
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}
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// This is nuts. If we were sane, we'd pass aElemAlign as a parameter to
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// this function. Unfortunately this function is called in nsTArray_base's
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// destructor, at which point we don't know elem_type's alignment.
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//
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// We'll fall on our face and return true when we should say false if
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//
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// * we're not using our auto buffer,
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// * aElemAlign == 4, and
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// * mHdr == GetAutoArrayBuffer(8).
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//
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// This could happen if |*this| lives on the heap and malloc allocated our
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// buffer on the heap adjacent to |*this|.
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//
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// However, we can show that this can't happen. If |this| is an auto array
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// (as we ensured at the beginning of the method), GetAutoArrayBuffer(8)
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// always points to memory owned by |*this|, because (as we assert below)
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//
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// * GetAutoArrayBuffer(8) is at most 4 bytes past GetAutoArrayBuffer(4), and
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// * sizeof(nsTArrayHeader) > 4.
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//
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// Since nsAutoTArray always contains an nsTArrayHeader,
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// GetAutoArrayBuffer(8) will always point inside the auto array object,
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// even if it doesn't point at the beginning of the header.
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//
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// Note that this means that we can't store elements with alignment 16 in an
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// nsTArray, because GetAutoArrayBuffer(16) could lie outside the memory
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// owned by this nsAutoTArray. We statically assert that elem_type's
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// alignment is 8 bytes or less in nsAutoArrayBase.
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static_assert(sizeof(nsTArrayHeader) > 4,
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"see comment above");
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#ifdef DEBUG
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ptrdiff_t diff = reinterpret_cast<const char*>(GetAutoArrayBuffer(8)) -
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reinterpret_cast<const char*>(GetAutoArrayBuffer(4));
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MOZ_ASSERT(diff >= 0 && diff <= 4,
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"GetAutoArrayBuffer doesn't do what we expect.");
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#endif
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return mHdr == GetAutoArrayBuffer(4) || mHdr == GetAutoArrayBuffer(8);
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}
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// defined in nsTArray.cpp
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bool IsTwiceTheRequiredBytesRepresentableAsUint32(size_t aCapacity,
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size_t aElemSize);
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template<class Alloc, class Copy>
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template<typename ActualAlloc>
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typename ActualAlloc::ResultTypeProxy
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nsTArray_base<Alloc, Copy>::EnsureCapacity(size_type aCapacity,
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size_type aElemSize)
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{
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// This should be the most common case so test this first
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if (aCapacity <= mHdr->mCapacity) {
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return ActualAlloc::SuccessResult();
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}
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// If the requested memory allocation exceeds size_type(-1)/2, then
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// our doubling algorithm may not be able to allocate it.
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// Additionally, if it exceeds uint32_t(-1) then we couldn't fit in the
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// Header::mCapacity member. Just bail out in cases like that. We don't want
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// to be allocating 2 GB+ arrays anyway.
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if (!IsTwiceTheRequiredBytesRepresentableAsUint32(aCapacity, aElemSize)) {
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ActualAlloc::SizeTooBig((size_t)aCapacity * aElemSize);
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return ActualAlloc::FailureResult();
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}
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size_t reqSize = sizeof(Header) + aCapacity * aElemSize;
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if (mHdr == EmptyHdr()) {
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// Malloc() new data
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Header* header = static_cast<Header*>(ActualAlloc::Malloc(reqSize));
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if (!header) {
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return ActualAlloc::FailureResult();
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}
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header->mLength = 0;
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header->mCapacity = aCapacity;
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header->mIsAutoArray = 0;
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mHdr = header;
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return ActualAlloc::SuccessResult();
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}
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// We increase our capacity so that the allocated buffer grows exponentially,
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// which gives us amortized O(1) appending. Below the threshold, we use
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// powers-of-two. Above the threshold, we grow by at least 1.125, rounding up
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// to the nearest MiB.
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const size_t slowGrowthThreshold = 8 * 1024 * 1024;
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size_t bytesToAlloc;
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if (reqSize >= slowGrowthThreshold) {
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size_t currSize = sizeof(Header) + Capacity() * aElemSize;
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size_t minNewSize = currSize + (currSize >> 3); // multiply by 1.125
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bytesToAlloc = reqSize > minNewSize ? reqSize : minNewSize;
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// Round up to the next multiple of MiB.
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const size_t MiB = 1 << 20;
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bytesToAlloc = MiB * ((bytesToAlloc + MiB - 1) / MiB);
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} else {
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// Round up to the next power of two.
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bytesToAlloc = mozilla::RoundUpPow2(reqSize);
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}
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Header* header;
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if (UsesAutoArrayBuffer() || !Copy::allowRealloc) {
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// Malloc() and copy
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header = static_cast<Header*>(ActualAlloc::Malloc(bytesToAlloc));
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if (!header) {
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return ActualAlloc::FailureResult();
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}
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Copy::CopyHeaderAndElements(header, mHdr, Length(), aElemSize);
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if (!UsesAutoArrayBuffer()) {
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ActualAlloc::Free(mHdr);
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}
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} else {
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// Realloc() existing data
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header = static_cast<Header*>(ActualAlloc::Realloc(mHdr, bytesToAlloc));
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if (!header) {
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return ActualAlloc::FailureResult();
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}
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}
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// How many elements can we fit in bytesToAlloc?
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size_t newCapacity = (bytesToAlloc - sizeof(Header)) / aElemSize;
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MOZ_ASSERT(newCapacity >= aCapacity, "Didn't enlarge the array enough!");
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header->mCapacity = newCapacity;
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mHdr = header;
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return ActualAlloc::SuccessResult();
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}
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// We don't need use Alloc template parameter specified here because failure to
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// shrink the capacity will leave the array unchanged.
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template<class Alloc, class Copy>
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void
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nsTArray_base<Alloc, Copy>::ShrinkCapacity(size_type aElemSize,
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size_t aElemAlign)
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{
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if (mHdr == EmptyHdr() || UsesAutoArrayBuffer()) {
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return;
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}
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if (mHdr->mLength >= mHdr->mCapacity) { // should never be greater than...
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return;
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}
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size_type length = Length();
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if (IsAutoArray() && GetAutoArrayBuffer(aElemAlign)->mCapacity >= length) {
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Header* header = GetAutoArrayBuffer(aElemAlign);
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// Copy data, but don't copy the header to avoid overwriting mCapacity
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header->mLength = length;
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Copy::CopyElements(header + 1, mHdr + 1, length, aElemSize);
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nsTArrayFallibleAllocator::Free(mHdr);
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mHdr = header;
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return;
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}
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if (length == 0) {
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MOZ_ASSERT(!IsAutoArray(), "autoarray should have fit 0 elements");
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nsTArrayFallibleAllocator::Free(mHdr);
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mHdr = EmptyHdr();
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return;
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}
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size_type size = sizeof(Header) + length * aElemSize;
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void* ptr = nsTArrayFallibleAllocator::Realloc(mHdr, size);
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if (!ptr) {
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return;
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}
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mHdr = static_cast<Header*>(ptr);
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mHdr->mCapacity = length;
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}
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template<class Alloc, class Copy>
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template<typename ActualAlloc>
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void
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nsTArray_base<Alloc, Copy>::ShiftData(index_type aStart,
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size_type aOldLen, size_type aNewLen,
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size_type aElemSize, size_t aElemAlign)
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{
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if (aOldLen == aNewLen) {
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return;
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}
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// Determine how many elements need to be shifted
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size_type num = mHdr->mLength - (aStart + aOldLen);
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// Compute the resulting length of the array
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mHdr->mLength += aNewLen - aOldLen;
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if (mHdr->mLength == 0) {
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ShrinkCapacity(aElemSize, aElemAlign);
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} else {
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// Maybe nothing needs to be shifted
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if (num == 0) {
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return;
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}
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// Perform shift (change units to bytes first)
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aStart *= aElemSize;
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aNewLen *= aElemSize;
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aOldLen *= aElemSize;
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char* baseAddr = reinterpret_cast<char*>(mHdr + 1) + aStart;
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Copy::MoveElements(baseAddr + aNewLen, baseAddr + aOldLen, num, aElemSize);
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}
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}
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template<class Alloc, class Copy>
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template<typename ActualAlloc>
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bool
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nsTArray_base<Alloc, Copy>::InsertSlotsAt(index_type aIndex, size_type aCount,
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size_type aElemSize,
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size_t aElemAlign)
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{
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MOZ_ASSERT(aIndex <= Length(), "Bogus insertion index");
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size_type newLen = Length() + aCount;
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EnsureCapacity<ActualAlloc>(newLen, aElemSize);
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// Check for out of memory conditions
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if (Capacity() < newLen) {
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return false;
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}
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// Move the existing elements as needed. Note that this will
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// change our mLength, so no need to call IncrementLength.
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ShiftData<ActualAlloc>(aIndex, 0, aCount, aElemSize, aElemAlign);
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return true;
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}
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// nsTArray_base::IsAutoArrayRestorer is an RAII class which takes
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// |nsTArray_base &array| in its constructor. When it's destructed, it ensures
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// that
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//
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// * array.mIsAutoArray has the same value as it did when we started, and
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// * if array has an auto buffer and mHdr would otherwise point to sEmptyHdr,
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// array.mHdr points to array's auto buffer.
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template<class Alloc, class Copy>
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nsTArray_base<Alloc, Copy>::IsAutoArrayRestorer::IsAutoArrayRestorer(
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nsTArray_base<Alloc, Copy>& aArray,
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size_t aElemAlign)
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: mArray(aArray)
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, mElemAlign(aElemAlign)
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, mIsAuto(aArray.IsAutoArray())
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{
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}
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template<class Alloc, class Copy>
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nsTArray_base<Alloc, Copy>::IsAutoArrayRestorer::~IsAutoArrayRestorer()
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{
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// Careful: We don't want to set mIsAutoArray = 1 on sEmptyHdr.
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if (mIsAuto && mArray.mHdr == mArray.EmptyHdr()) {
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// Call GetAutoArrayBufferUnsafe() because GetAutoArrayBuffer() asserts
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// that mHdr->mIsAutoArray is true, which surely isn't the case here.
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mArray.mHdr = mArray.GetAutoArrayBufferUnsafe(mElemAlign);
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mArray.mHdr->mLength = 0;
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} else if (mArray.mHdr != mArray.EmptyHdr()) {
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mArray.mHdr->mIsAutoArray = mIsAuto;
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}
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}
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template<class Alloc, class Copy>
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template<typename ActualAlloc, class Allocator>
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typename ActualAlloc::ResultTypeProxy
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nsTArray_base<Alloc, Copy>::SwapArrayElements(nsTArray_base<Allocator,
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Copy>& aOther,
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size_type aElemSize,
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size_t aElemAlign)
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{
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// EnsureNotUsingAutoArrayBuffer will set mHdr = sEmptyHdr even if we have an
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// auto buffer. We need to point mHdr back to our auto buffer before we
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// return, otherwise we'll forget that we have an auto buffer at all!
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// IsAutoArrayRestorer takes care of this for us.
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IsAutoArrayRestorer ourAutoRestorer(*this, aElemAlign);
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typename nsTArray_base<Allocator, Copy>::IsAutoArrayRestorer
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otherAutoRestorer(aOther, aElemAlign);
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// If neither array uses an auto buffer which is big enough to store the
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// other array's elements, then ensure that both arrays use malloc'ed storage
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// and swap their mHdr pointers.
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if ((!UsesAutoArrayBuffer() || Capacity() < aOther.Length()) &&
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(!aOther.UsesAutoArrayBuffer() || aOther.Capacity() < Length())) {
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if (!EnsureNotUsingAutoArrayBuffer<ActualAlloc>(aElemSize) ||
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!aOther.template EnsureNotUsingAutoArrayBuffer<ActualAlloc>(aElemSize)) {
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return ActualAlloc::FailureResult();
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}
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Header* temp = mHdr;
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mHdr = aOther.mHdr;
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aOther.mHdr = temp;
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return ActualAlloc::SuccessResult();
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}
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// Swap the two arrays by copying, since at least one is using an auto
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// buffer which is large enough to hold all of the aOther's elements. We'll
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// copy the shorter array into temporary storage.
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//
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// (We could do better than this in some circumstances. Suppose we're
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// swapping arrays X and Y. X has space for 2 elements in its auto buffer,
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// but currently has length 4, so it's using malloc'ed storage. Y has length
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// 2. When we swap X and Y, we don't need to use a temporary buffer; we can
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// write Y straight into X's auto buffer, write X's malloc'ed buffer on top
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// of Y, and then switch X to using its auto buffer.)
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if (!ActualAlloc::Successful(EnsureCapacity<ActualAlloc>(aOther.Length(), aElemSize)) ||
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!Allocator::Successful(aOther.template EnsureCapacity<Allocator>(Length(), aElemSize))) {
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return ActualAlloc::FailureResult();
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}
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// The EnsureCapacity calls above shouldn't have caused *both* arrays to
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// switch from their auto buffers to malloc'ed space.
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MOZ_ASSERT(UsesAutoArrayBuffer() || aOther.UsesAutoArrayBuffer(),
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"One of the arrays should be using its auto buffer.");
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size_type smallerLength = XPCOM_MIN(Length(), aOther.Length());
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size_type largerLength = XPCOM_MAX(Length(), aOther.Length());
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void* smallerElements;
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void* largerElements;
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if (Length() <= aOther.Length()) {
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smallerElements = Hdr() + 1;
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largerElements = aOther.Hdr() + 1;
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} else {
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smallerElements = aOther.Hdr() + 1;
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largerElements = Hdr() + 1;
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}
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// Allocate temporary storage for the smaller of the two arrays. We want to
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// allocate this space on the stack, if it's not too large. Sounds like a
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// job for AutoTArray! (One of the two arrays we're swapping is using an
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// auto buffer, so we're likely not allocating a lot of space here. But one
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// could, in theory, allocate a huge AutoTArray on the heap.)
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nsAutoArrayBase<nsTArray_Impl<uint8_t, ActualAlloc>, 64> temp;
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if (!ActualAlloc::Successful(temp.template EnsureCapacity<ActualAlloc>(smallerLength,
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aElemSize))) {
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return ActualAlloc::FailureResult();
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}
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Copy::CopyElements(temp.Elements(), smallerElements, smallerLength, aElemSize);
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Copy::CopyElements(smallerElements, largerElements, largerLength, aElemSize);
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Copy::CopyElements(largerElements, temp.Elements(), smallerLength, aElemSize);
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// Swap the arrays' lengths.
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MOZ_ASSERT((aOther.Length() == 0 || mHdr != EmptyHdr()) &&
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(Length() == 0 || aOther.mHdr != EmptyHdr()),
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"Don't set sEmptyHdr's length.");
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size_type tempLength = Length();
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// Avoid writing to EmptyHdr, since it can trigger false
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// positives with TSan.
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if (mHdr != EmptyHdr()) {
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mHdr->mLength = aOther.Length();
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}
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if (aOther.mHdr != EmptyHdr()) {
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aOther.mHdr->mLength = tempLength;
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}
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return ActualAlloc::SuccessResult();
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}
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template<class Alloc, class Copy>
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template<typename ActualAlloc>
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bool
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nsTArray_base<Alloc, Copy>::EnsureNotUsingAutoArrayBuffer(size_type aElemSize)
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{
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if (UsesAutoArrayBuffer()) {
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// If you call this on a 0-length array, we'll set that array's mHdr to
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// sEmptyHdr, in flagrant violation of the nsAutoTArray invariants. It's
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// up to you to set it back! (If you don't, the nsAutoTArray will forget
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// that it has an auto buffer.)
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if (Length() == 0) {
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mHdr = EmptyHdr();
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return true;
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}
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size_type size = sizeof(Header) + Length() * aElemSize;
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Header* header = static_cast<Header*>(ActualAlloc::Malloc(size));
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if (!header) {
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return false;
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}
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Copy::CopyHeaderAndElements(header, mHdr, Length(), aElemSize);
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header->mCapacity = Length();
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mHdr = header;
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}
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return true;
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}
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