1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/xpcom/glue/nsTArray-inl.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,420 @@
1.4 +/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
1.5 +/* vim:set ts=2 sw=2 sts=2 et cindent: */
1.6 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.7 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.8 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.9 +
1.10 +#ifndef nsTArray_h__
1.11 +# error "Don't include this file directly"
1.12 +#endif
1.13 +
1.14 +template<class Alloc, class Copy>
1.15 +nsTArray_base<Alloc, Copy>::nsTArray_base()
1.16 + : mHdr(EmptyHdr()) {
1.17 + MOZ_COUNT_CTOR(nsTArray_base);
1.18 +}
1.19 +
1.20 +template<class Alloc, class Copy>
1.21 +nsTArray_base<Alloc, Copy>::~nsTArray_base() {
1.22 + if (mHdr != EmptyHdr() && !UsesAutoArrayBuffer()) {
1.23 + Alloc::Free(mHdr);
1.24 + }
1.25 + MOZ_COUNT_DTOR(nsTArray_base);
1.26 +}
1.27 +
1.28 +template<class Alloc, class Copy>
1.29 +const nsTArrayHeader* nsTArray_base<Alloc, Copy>::GetAutoArrayBufferUnsafe(size_t elemAlign) const {
1.30 + // Assuming |this| points to an nsAutoArray, we want to get a pointer to
1.31 + // mAutoBuf. So just cast |this| to nsAutoArray* and read &mAutoBuf!
1.32 +
1.33 + const void* autoBuf = &reinterpret_cast<const nsAutoArrayBase<nsTArray<uint32_t>, 1>*>(this)->mAutoBuf;
1.34 +
1.35 + // If we're on a 32-bit system and elemAlign is 8, we need to adjust our
1.36 + // pointer to take into account the extra alignment in the auto array.
1.37 +
1.38 + static_assert(sizeof(void*) != 4 ||
1.39 + (MOZ_ALIGNOF(mozilla::AlignedElem<8>) == 8 &&
1.40 + sizeof(nsAutoTArray<mozilla::AlignedElem<8>, 1>) ==
1.41 + sizeof(void*) + sizeof(nsTArrayHeader) +
1.42 + 4 + sizeof(mozilla::AlignedElem<8>)),
1.43 + "auto array padding wasn't what we expected");
1.44 +
1.45 + // We don't support alignments greater than 8 bytes.
1.46 + NS_ABORT_IF_FALSE(elemAlign <= 4 || elemAlign == 8, "unsupported alignment.");
1.47 + if (sizeof(void*) == 4 && elemAlign == 8) {
1.48 + autoBuf = reinterpret_cast<const char*>(autoBuf) + 4;
1.49 + }
1.50 +
1.51 + return reinterpret_cast<const Header*>(autoBuf);
1.52 +}
1.53 +
1.54 +template<class Alloc, class Copy>
1.55 +bool nsTArray_base<Alloc, Copy>::UsesAutoArrayBuffer() const {
1.56 + if (!mHdr->mIsAutoArray) {
1.57 + return false;
1.58 + }
1.59 +
1.60 + // This is nuts. If we were sane, we'd pass elemAlign as a parameter to
1.61 + // this function. Unfortunately this function is called in nsTArray_base's
1.62 + // destructor, at which point we don't know elem_type's alignment.
1.63 + //
1.64 + // We'll fall on our face and return true when we should say false if
1.65 + //
1.66 + // * we're not using our auto buffer,
1.67 + // * elemAlign == 4, and
1.68 + // * mHdr == GetAutoArrayBuffer(8).
1.69 + //
1.70 + // This could happen if |*this| lives on the heap and malloc allocated our
1.71 + // buffer on the heap adjacent to |*this|.
1.72 + //
1.73 + // However, we can show that this can't happen. If |this| is an auto array
1.74 + // (as we ensured at the beginning of the method), GetAutoArrayBuffer(8)
1.75 + // always points to memory owned by |*this|, because (as we assert below)
1.76 + //
1.77 + // * GetAutoArrayBuffer(8) is at most 4 bytes past GetAutoArrayBuffer(4), and
1.78 + // * sizeof(nsTArrayHeader) > 4.
1.79 + //
1.80 + // Since nsAutoTArray always contains an nsTArrayHeader,
1.81 + // GetAutoArrayBuffer(8) will always point inside the auto array object,
1.82 + // even if it doesn't point at the beginning of the header.
1.83 + //
1.84 + // Note that this means that we can't store elements with alignment 16 in an
1.85 + // nsTArray, because GetAutoArrayBuffer(16) could lie outside the memory
1.86 + // owned by this nsAutoTArray. We statically assert that elem_type's
1.87 + // alignment is 8 bytes or less in nsAutoArrayBase.
1.88 +
1.89 + static_assert(sizeof(nsTArrayHeader) > 4,
1.90 + "see comment above");
1.91 +
1.92 +#ifdef DEBUG
1.93 + ptrdiff_t diff = reinterpret_cast<const char*>(GetAutoArrayBuffer(8)) -
1.94 + reinterpret_cast<const char*>(GetAutoArrayBuffer(4));
1.95 + NS_ABORT_IF_FALSE(diff >= 0 && diff <= 4, "GetAutoArrayBuffer doesn't do what we expect.");
1.96 +#endif
1.97 +
1.98 + return mHdr == GetAutoArrayBuffer(4) || mHdr == GetAutoArrayBuffer(8);
1.99 +}
1.100 +
1.101 +
1.102 +template<class Alloc, class Copy>
1.103 +typename Alloc::ResultTypeProxy
1.104 +nsTArray_base<Alloc, Copy>::EnsureCapacity(size_type capacity, size_type elemSize) {
1.105 + // This should be the most common case so test this first
1.106 + if (capacity <= mHdr->mCapacity)
1.107 + return Alloc::SuccessResult();
1.108 +
1.109 + // If the requested memory allocation exceeds size_type(-1)/2, then
1.110 + // our doubling algorithm may not be able to allocate it.
1.111 + // Additionally we couldn't fit in the Header::mCapacity
1.112 + // member. Just bail out in cases like that. We don't want to be
1.113 + // allocating 2 GB+ arrays anyway.
1.114 + if ((uint64_t)capacity * elemSize > size_type(-1)/2) {
1.115 + Alloc::SizeTooBig((size_t)capacity * elemSize);
1.116 + return Alloc::FailureResult();
1.117 + }
1.118 +
1.119 + if (mHdr == EmptyHdr()) {
1.120 + // Malloc() new data
1.121 + Header *header = static_cast<Header*>
1.122 + (Alloc::Malloc(sizeof(Header) + capacity * elemSize));
1.123 + if (!header)
1.124 + return Alloc::FailureResult();
1.125 + header->mLength = 0;
1.126 + header->mCapacity = capacity;
1.127 + header->mIsAutoArray = 0;
1.128 + mHdr = header;
1.129 +
1.130 + return Alloc::SuccessResult();
1.131 + }
1.132 +
1.133 + // We increase our capacity so |capacity * elemSize + sizeof(Header)| is the
1.134 + // next power of two, if this value is less than pageSize bytes, or otherwise
1.135 + // so it's the next multiple of pageSize.
1.136 + const uint32_t pageSizeBytes = 12;
1.137 + const uint32_t pageSize = 1 << pageSizeBytes;
1.138 +
1.139 + uint32_t minBytes = capacity * elemSize + sizeof(Header);
1.140 + uint32_t bytesToAlloc;
1.141 + if (minBytes >= pageSize) {
1.142 + // Round up to the next multiple of pageSize.
1.143 + bytesToAlloc = pageSize * ((minBytes + pageSize - 1) / pageSize);
1.144 + }
1.145 + else {
1.146 + // Round up to the next power of two. See
1.147 + // http://graphics.stanford.edu/~seander/bithacks.html
1.148 + bytesToAlloc = minBytes - 1;
1.149 + bytesToAlloc |= bytesToAlloc >> 1;
1.150 + bytesToAlloc |= bytesToAlloc >> 2;
1.151 + bytesToAlloc |= bytesToAlloc >> 4;
1.152 + bytesToAlloc |= bytesToAlloc >> 8;
1.153 + bytesToAlloc |= bytesToAlloc >> 16;
1.154 + bytesToAlloc++;
1.155 +
1.156 + MOZ_ASSERT((bytesToAlloc & (bytesToAlloc - 1)) == 0,
1.157 + "nsTArray's allocation size should be a power of two!");
1.158 + }
1.159 +
1.160 + Header *header;
1.161 + if (UsesAutoArrayBuffer() || !Copy::allowRealloc) {
1.162 + // Malloc() and copy
1.163 + header = static_cast<Header*>(Alloc::Malloc(bytesToAlloc));
1.164 + if (!header)
1.165 + return Alloc::FailureResult();
1.166 +
1.167 + Copy::CopyHeaderAndElements(header, mHdr, Length(), elemSize);
1.168 +
1.169 + if (!UsesAutoArrayBuffer())
1.170 + Alloc::Free(mHdr);
1.171 + } else {
1.172 + // Realloc() existing data
1.173 + header = static_cast<Header*>(Alloc::Realloc(mHdr, bytesToAlloc));
1.174 + if (!header)
1.175 + return Alloc::FailureResult();
1.176 + }
1.177 +
1.178 + // How many elements can we fit in bytesToAlloc?
1.179 + uint32_t newCapacity = (bytesToAlloc - sizeof(Header)) / elemSize;
1.180 + MOZ_ASSERT(newCapacity >= capacity, "Didn't enlarge the array enough!");
1.181 + header->mCapacity = newCapacity;
1.182 +
1.183 + mHdr = header;
1.184 +
1.185 + return Alloc::SuccessResult();
1.186 +}
1.187 +
1.188 +template<class Alloc, class Copy>
1.189 +void
1.190 +nsTArray_base<Alloc, Copy>::ShrinkCapacity(size_type elemSize, size_t elemAlign) {
1.191 + if (mHdr == EmptyHdr() || UsesAutoArrayBuffer())
1.192 + return;
1.193 +
1.194 + if (mHdr->mLength >= mHdr->mCapacity) // should never be greater than...
1.195 + return;
1.196 +
1.197 + size_type length = Length();
1.198 +
1.199 + if (IsAutoArray() && GetAutoArrayBuffer(elemAlign)->mCapacity >= length) {
1.200 + Header* header = GetAutoArrayBuffer(elemAlign);
1.201 +
1.202 + // Copy data, but don't copy the header to avoid overwriting mCapacity
1.203 + header->mLength = length;
1.204 + Copy::CopyElements(header + 1, mHdr + 1, length, elemSize);
1.205 +
1.206 + Alloc::Free(mHdr);
1.207 + mHdr = header;
1.208 + return;
1.209 + }
1.210 +
1.211 + if (length == 0) {
1.212 + MOZ_ASSERT(!IsAutoArray(), "autoarray should have fit 0 elements");
1.213 + Alloc::Free(mHdr);
1.214 + mHdr = EmptyHdr();
1.215 + return;
1.216 + }
1.217 +
1.218 + size_type size = sizeof(Header) + length * elemSize;
1.219 + void *ptr = Alloc::Realloc(mHdr, size);
1.220 + if (!ptr)
1.221 + return;
1.222 + mHdr = static_cast<Header*>(ptr);
1.223 + mHdr->mCapacity = length;
1.224 +}
1.225 +
1.226 +template<class Alloc, class Copy>
1.227 +void
1.228 +nsTArray_base<Alloc, Copy>::ShiftData(index_type start,
1.229 + size_type oldLen, size_type newLen,
1.230 + size_type elemSize, size_t elemAlign) {
1.231 + if (oldLen == newLen)
1.232 + return;
1.233 +
1.234 + // Determine how many elements need to be shifted
1.235 + size_type num = mHdr->mLength - (start + oldLen);
1.236 +
1.237 + // Compute the resulting length of the array
1.238 + mHdr->mLength += newLen - oldLen;
1.239 + if (mHdr->mLength == 0) {
1.240 + ShrinkCapacity(elemSize, elemAlign);
1.241 + } else {
1.242 + // Maybe nothing needs to be shifted
1.243 + if (num == 0)
1.244 + return;
1.245 + // Perform shift (change units to bytes first)
1.246 + start *= elemSize;
1.247 + newLen *= elemSize;
1.248 + oldLen *= elemSize;
1.249 + char *base = reinterpret_cast<char*>(mHdr + 1) + start;
1.250 + Copy::MoveElements(base + newLen, base + oldLen, num, elemSize);
1.251 + }
1.252 +}
1.253 +
1.254 +template<class Alloc, class Copy>
1.255 +bool
1.256 +nsTArray_base<Alloc, Copy>::InsertSlotsAt(index_type index, size_type count,
1.257 + size_type elementSize, size_t elemAlign) {
1.258 + MOZ_ASSERT(index <= Length(), "Bogus insertion index");
1.259 + size_type newLen = Length() + count;
1.260 +
1.261 + EnsureCapacity(newLen, elementSize);
1.262 +
1.263 + // Check for out of memory conditions
1.264 + if (Capacity() < newLen)
1.265 + return false;
1.266 +
1.267 + // Move the existing elements as needed. Note that this will
1.268 + // change our mLength, so no need to call IncrementLength.
1.269 + ShiftData(index, 0, count, elementSize, elemAlign);
1.270 +
1.271 + return true;
1.272 +}
1.273 +
1.274 +// nsTArray_base::IsAutoArrayRestorer is an RAII class which takes
1.275 +// |nsTArray_base &array| in its constructor. When it's destructed, it ensures
1.276 +// that
1.277 +//
1.278 +// * array.mIsAutoArray has the same value as it did when we started, and
1.279 +// * if array has an auto buffer and mHdr would otherwise point to sEmptyHdr,
1.280 +// array.mHdr points to array's auto buffer.
1.281 +
1.282 +template<class Alloc, class Copy>
1.283 +nsTArray_base<Alloc, Copy>::IsAutoArrayRestorer::IsAutoArrayRestorer(
1.284 + nsTArray_base<Alloc, Copy> &array,
1.285 + size_t elemAlign)
1.286 + : mArray(array),
1.287 + mElemAlign(elemAlign),
1.288 + mIsAuto(array.IsAutoArray())
1.289 +{
1.290 +}
1.291 +
1.292 +template<class Alloc, class Copy>
1.293 +nsTArray_base<Alloc, Copy>::IsAutoArrayRestorer::~IsAutoArrayRestorer() {
1.294 + // Careful: We don't want to set mIsAutoArray = 1 on sEmptyHdr.
1.295 + if (mIsAuto && mArray.mHdr == mArray.EmptyHdr()) {
1.296 + // Call GetAutoArrayBufferUnsafe() because GetAutoArrayBuffer() asserts
1.297 + // that mHdr->mIsAutoArray is true, which surely isn't the case here.
1.298 + mArray.mHdr = mArray.GetAutoArrayBufferUnsafe(mElemAlign);
1.299 + mArray.mHdr->mLength = 0;
1.300 + }
1.301 + else if (mArray.mHdr != mArray.EmptyHdr()) {
1.302 + mArray.mHdr->mIsAutoArray = mIsAuto;
1.303 + }
1.304 +}
1.305 +
1.306 +template<class Alloc, class Copy>
1.307 +template<class Allocator>
1.308 +typename Alloc::ResultTypeProxy
1.309 +nsTArray_base<Alloc, Copy>::SwapArrayElements(nsTArray_base<Allocator, Copy>& other,
1.310 + size_type elemSize, size_t elemAlign) {
1.311 +
1.312 + // EnsureNotUsingAutoArrayBuffer will set mHdr = sEmptyHdr even if we have an
1.313 + // auto buffer. We need to point mHdr back to our auto buffer before we
1.314 + // return, otherwise we'll forget that we have an auto buffer at all!
1.315 + // IsAutoArrayRestorer takes care of this for us.
1.316 +
1.317 + IsAutoArrayRestorer ourAutoRestorer(*this, elemAlign);
1.318 + typename nsTArray_base<Allocator, Copy>::IsAutoArrayRestorer otherAutoRestorer(other, elemAlign);
1.319 +
1.320 + // If neither array uses an auto buffer which is big enough to store the
1.321 + // other array's elements, then ensure that both arrays use malloc'ed storage
1.322 + // and swap their mHdr pointers.
1.323 + if ((!UsesAutoArrayBuffer() || Capacity() < other.Length()) &&
1.324 + (!other.UsesAutoArrayBuffer() || other.Capacity() < Length())) {
1.325 +
1.326 + if (!EnsureNotUsingAutoArrayBuffer(elemSize) ||
1.327 + !other.EnsureNotUsingAutoArrayBuffer(elemSize)) {
1.328 + return Alloc::FailureResult();
1.329 + }
1.330 +
1.331 + Header *temp = mHdr;
1.332 + mHdr = other.mHdr;
1.333 + other.mHdr = temp;
1.334 +
1.335 + return Alloc::SuccessResult();
1.336 + }
1.337 +
1.338 + // Swap the two arrays by copying, since at least one is using an auto
1.339 + // buffer which is large enough to hold all of the other's elements. We'll
1.340 + // copy the shorter array into temporary storage.
1.341 + //
1.342 + // (We could do better than this in some circumstances. Suppose we're
1.343 + // swapping arrays X and Y. X has space for 2 elements in its auto buffer,
1.344 + // but currently has length 4, so it's using malloc'ed storage. Y has length
1.345 + // 2. When we swap X and Y, we don't need to use a temporary buffer; we can
1.346 + // write Y straight into X's auto buffer, write X's malloc'ed buffer on top
1.347 + // of Y, and then switch X to using its auto buffer.)
1.348 +
1.349 + if (!Alloc::Successful(EnsureCapacity(other.Length(), elemSize)) ||
1.350 + !Allocator::Successful(other.EnsureCapacity(Length(), elemSize))) {
1.351 + return Alloc::FailureResult();
1.352 + }
1.353 +
1.354 + // The EnsureCapacity calls above shouldn't have caused *both* arrays to
1.355 + // switch from their auto buffers to malloc'ed space.
1.356 + NS_ABORT_IF_FALSE(UsesAutoArrayBuffer() ||
1.357 + other.UsesAutoArrayBuffer(),
1.358 + "One of the arrays should be using its auto buffer.");
1.359 +
1.360 + size_type smallerLength = XPCOM_MIN(Length(), other.Length());
1.361 + size_type largerLength = XPCOM_MAX(Length(), other.Length());
1.362 + void *smallerElements, *largerElements;
1.363 + if (Length() <= other.Length()) {
1.364 + smallerElements = Hdr() + 1;
1.365 + largerElements = other.Hdr() + 1;
1.366 + }
1.367 + else {
1.368 + smallerElements = other.Hdr() + 1;
1.369 + largerElements = Hdr() + 1;
1.370 + }
1.371 +
1.372 + // Allocate temporary storage for the smaller of the two arrays. We want to
1.373 + // allocate this space on the stack, if it's not too large. Sounds like a
1.374 + // job for AutoTArray! (One of the two arrays we're swapping is using an
1.375 + // auto buffer, so we're likely not allocating a lot of space here. But one
1.376 + // could, in theory, allocate a huge AutoTArray on the heap.)
1.377 + nsAutoArrayBase<nsTArray_Impl<uint8_t, Alloc>, 64> temp;
1.378 + if (!Alloc::Successful(temp.EnsureCapacity(smallerLength, elemSize))) {
1.379 + return Alloc::FailureResult();
1.380 + }
1.381 +
1.382 + Copy::CopyElements(temp.Elements(), smallerElements, smallerLength, elemSize);
1.383 + Copy::CopyElements(smallerElements, largerElements, largerLength, elemSize);
1.384 + Copy::CopyElements(largerElements, temp.Elements(), smallerLength, elemSize);
1.385 +
1.386 + // Swap the arrays' lengths.
1.387 + NS_ABORT_IF_FALSE((other.Length() == 0 || mHdr != EmptyHdr()) &&
1.388 + (Length() == 0 || other.mHdr != EmptyHdr()),
1.389 + "Don't set sEmptyHdr's length.");
1.390 + size_type tempLength = Length();
1.391 + mHdr->mLength = other.Length();
1.392 + other.mHdr->mLength = tempLength;
1.393 +
1.394 + return Alloc::SuccessResult();
1.395 +}
1.396 +
1.397 +template<class Alloc, class Copy>
1.398 +bool
1.399 +nsTArray_base<Alloc, Copy>::EnsureNotUsingAutoArrayBuffer(size_type elemSize) {
1.400 + if (UsesAutoArrayBuffer()) {
1.401 +
1.402 + // If you call this on a 0-length array, we'll set that array's mHdr to
1.403 + // sEmptyHdr, in flagrant violation of the nsAutoTArray invariants. It's
1.404 + // up to you to set it back! (If you don't, the nsAutoTArray will forget
1.405 + // that it has an auto buffer.)
1.406 + if (Length() == 0) {
1.407 + mHdr = EmptyHdr();
1.408 + return true;
1.409 + }
1.410 +
1.411 + size_type size = sizeof(Header) + Length() * elemSize;
1.412 +
1.413 + Header* header = static_cast<Header*>(Alloc::Malloc(size));
1.414 + if (!header)
1.415 + return false;
1.416 +
1.417 + Copy::CopyHeaderAndElements(header, mHdr, Length(), elemSize);
1.418 + header->mCapacity = Length();
1.419 + mHdr = header;
1.420 + }
1.421 +
1.422 + return true;
1.423 +}
