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Refine {QString, QBA}::reallocData() logic

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Fixed misleading naming of "slowReallocatePath". It's no longer "slow",
it's downright dangerous now to reallocate under certain conditions

While at it, added extra assert to QArrayData::reallocateUnaligned()
and cleaned up that function a bit

Change-Id: I05921fb5058eb563997e66107566c87fb4ea5599
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Andrei Golubev 2020-11-03 11:26:20 +01:00
parent 42f8afc2dc
commit 504972f838
3 changed files with 14 additions and 13 deletions
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9
src/corelib/text/qbytearray.cpp
View File

@ -1708,12 +1708,11 @@ void QByteArray::reallocData(qsizetype alloc, QArrayData::AllocationOption optio
return;
}
// there's a case of slow reallocate path where we need to memmove the data
// before a call to ::realloc(), meaning that there's an extra "heavy"
// operation. just prefer ::malloc() branch in this case
const bool slowReallocatePath = d.freeSpaceAtBegin() > 0;
// don't use reallocate path when reducing capacity and there's free space
// at the beginning: might shift data pointer outside of allocated space
const bool cannotUseReallocate = d.freeSpaceAtBegin() > 0 && alloc < d.constAllocatedCapacity();
if (d->needsDetach() || slowReallocatePath) {
if (d->needsDetach() || cannotUseReallocate) {
DataPointer dd(Data::allocate(alloc, option), qMin(alloc, d.size));
if (dd.size > 0)
::memcpy(dd.data(), d.data(), dd.size);

9
src/corelib/text/qstring.cpp
View File

@ -2504,12 +2504,11 @@ void QString::reallocData(qsizetype alloc, QArrayData::AllocationOption option)
return;
}
// there's a case of slow reallocate path where we need to memmove the data
// before a call to ::realloc(), meaning that there's an extra "heavy"
// operation. just prefer ::malloc() branch in this case
const bool slowReallocatePath = d.freeSpaceAtBegin() > 0;
// don't use reallocate path when reducing capacity and there's free space
// at the beginning: might shift data pointer outside of allocated space
const bool cannotUseReallocate = d.freeSpaceAtBegin() > 0 && alloc < d.constAllocatedCapacity();
if (d->needsDetach() || slowReallocatePath) {
if (d->needsDetach() || cannotUseReallocate) {
DataPointer dd(Data::allocate(alloc, option), qMin(alloc, d.size));
if (dd.size > 0)
::memcpy(dd.data(), d.data(), dd.size * sizeof(QChar));

9
src/corelib/tools/qarraydata.cpp
View File

@ -233,10 +233,13 @@ QArrayData::reallocateUnaligned(QArrayData *data, void *dataPointer,
{
Q_ASSERT(!data || !data->isShared());
qsizetype headerSize = sizeof(QArrayData);
const qsizetype headerSize = sizeof(QArrayData);
qsizetype allocSize = calculateBlockSize(capacity, objectSize, headerSize, option);
qptrdiff offset = dataPointer ? reinterpret_cast<char *>(dataPointer) - reinterpret_cast<char *>(data) : headerSize;
const qptrdiff offset = dataPointer
? reinterpret_cast<char *>(dataPointer) - reinterpret_cast<char *>(data)
: headerSize;
Q_ASSERT(offset > 0);
Q_ASSERT(offset <= allocSize); // == when all free space is at the beginning
allocSize = reserveExtraBytes(allocSize);
if (Q_UNLIKELY(allocSize < 0)) // handle overflow. cannot reallocate reliably
@ -244,7 +247,7 @@ QArrayData::reallocateUnaligned(QArrayData *data, void *dataPointer,
QArrayData *header = static_cast<QArrayData *>(::realloc(data, size_t(allocSize)));
if (header) {
header->alloc = uint(capacity);
header->alloc = capacity;
dataPointer = reinterpret_cast<char *>(header) + offset;
} else {
dataPointer = nullptr;