diff options
author | Andrei Golubev <andrei.golubev@qt.io> | 2020-10-29 14:25:48 +0100 |
---|---|---|
committer | Lars Knoll <lars.knoll@qt.io> | 2020-11-04 11:21:12 +0100 |
commit | 7eed57511a786861b513af089aef48651fed7891 (patch) | |
tree | f6eeaa99bbea63af1207d7d3a64e6e87ce051c28 /src/corelib/text/qbytearray.cpp | |
parent | 12718e5ea289df1d3f113bf0ff4e64ea8961e20d (diff) |
QArrayDataPointer: redesign (and simplify) growth policy
It looks like we can drastically simplify the way QADP grows without
sacrificing much:
1. append-only use cases should have the same performance as before
2. prepend-only use cases should (with the help of other commits) get
additional performance speedup
3. mid-insertion is harder to reason about, but it is either unchanged
or benefits a bit as there's some free space at both ends now
4. mixed prepend/append cases are weird and would keep excess free
space around but this is less critical and overall less used AFAIK
Now, QList would actually start to feel like a double-ended container
instead of "it's QVector but with faster prepend". This commit should
help close the performance gap between 6.0 and 5.15 as well
As a drawback, we will most likely have more space allocated in mixed
and mid-insert cases. This needs to be checked
Task-number: QTBUG-86583
Change-Id: I7c6ede896144920fe01862b9fe789c8fdfc11f80
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Diffstat (limited to 'src/corelib/text/qbytearray.cpp')
-rw-r--r-- | src/corelib/text/qbytearray.cpp | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp index c6dbf4c7aa..e550224c4c 100644 --- a/src/corelib/text/qbytearray.cpp +++ b/src/corelib/text/qbytearray.cpp @@ -1728,7 +1728,11 @@ void QByteArray::reallocGrowData(qsizetype alloc, Data::ArrayOptions options) if (!alloc) // expected to always allocate alloc = 1; - if (d->needsDetach()) { + // when we're requested to grow backwards, it means we're in prepend-like + // case. realloc() is good, but we might actually get more free space at the + // beginning with a call to allocateGrow, so prefer that instead + const bool preferAllocateGrow = options & Data::GrowsBackwards; + if (d->needsDetach() || preferAllocateGrow) { const auto newSize = qMin(alloc, d.size); DataPointer dd(DataPointer::allocateGrow(d, alloc, newSize, options)); dd->copyAppend(d.data(), d.data() + newSize); |