gecko-dev/xpcom/glue/nsTArray-inl.h

420 lines
14 KiB
C++

/* -*- 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>
nsTArray_base<Alloc>::nsTArray_base()
: mHdr(EmptyHdr()) {
MOZ_COUNT_CTOR(nsTArray_base);
}
template<class Alloc>
nsTArray_base<Alloc>::~nsTArray_base() {
if (mHdr != EmptyHdr() && !UsesAutoArrayBuffer()) {
Alloc::Free(mHdr);
}
MOZ_COUNT_DTOR(nsTArray_base);
}
template<class Alloc>
const nsTArrayHeader* nsTArray_base<Alloc>::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.
MOZ_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>
bool nsTArray_base<Alloc>::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.
MOZ_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>
bool
nsTArray_base<Alloc>::EnsureCapacity(size_type capacity, size_type elemSize) {
// This should be the most common case so test this first
if (capacity <= mHdr->mCapacity)
return true;
// 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();
return false;
}
if (mHdr == EmptyHdr()) {
// Malloc() new data
Header *header = static_cast<Header*>
(Alloc::Malloc(sizeof(Header) + capacity * elemSize));
if (!header)
return false;
header->mLength = 0;
header->mCapacity = capacity;
header->mIsAutoArray = 0;
mHdr = header;
return true;
}
// 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()) {
// Malloc() and copy
header = static_cast<Header*>(Alloc::Malloc(bytesToAlloc));
if (!header)
return false;
memcpy(header, mHdr, sizeof(Header) + Length() * elemSize);
} else {
// Realloc() existing data
header = static_cast<Header*>(Alloc::Realloc(mHdr, bytesToAlloc));
if (!header)
return false;
}
// 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 true;
}
template<class Alloc>
void
nsTArray_base<Alloc>::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;
memcpy(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>
void
nsTArray_base<Alloc>::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;
num *= elemSize;
char *base = reinterpret_cast<char*>(mHdr + 1) + start;
memmove(base + newLen, base + oldLen, num);
}
}
template<class Alloc>
bool
nsTArray_base<Alloc>::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>
nsTArray_base<Alloc>::IsAutoArrayRestorer::IsAutoArrayRestorer(
nsTArray_base<Alloc> &array,
size_t elemAlign)
: mArray(array),
mElemAlign(elemAlign),
mIsAuto(array.IsAutoArray())
{
}
template<class Alloc>
nsTArray_base<Alloc>::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 {
mArray.mHdr->mIsAutoArray = mIsAuto;
}
}
template<class Alloc>
template<class Allocator>
bool
nsTArray_base<Alloc>::SwapArrayElements(nsTArray_base<Allocator>& 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>::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 false;
}
Header *temp = mHdr;
mHdr = other.mHdr;
other.mHdr = temp;
return true;
}
// Swap the two arrays using memcpy, 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 (!EnsureCapacity(other.Length(), elemSize) ||
!other.EnsureCapacity(Length(), elemSize)) {
return false;
}
// 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 = NS_MIN(Length(), other.Length());
size_type largerLength = NS_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.)
nsAutoTArray<uint8_t, 64, Alloc> temp;
if (!temp.SetCapacity(smallerLength * elemSize)) {
return false;
}
memcpy(temp.Elements(), smallerElements, smallerLength * elemSize);
memcpy(smallerElements, largerElements, largerLength * elemSize);
memcpy(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 true;
}
template<class Alloc>
bool
nsTArray_base<Alloc>::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;
memcpy(header, mHdr, size);
header->mCapacity = Length();
mHdr = header;
}
return true;
}