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QHash/QSet: fix squeeze() for default-constructed container

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QHash::squeeze() was unconditionally calling reserve(0), which is
always allocating memory (even for 0 size).
This was leading to a confusing situation when calling squeeze() on
a default-constructed container with 0 capacity() actually allocated
memory. This is very misleading, as squeeze() is supposed to free
unneeded memory, not to allocate more.

This patch adds a check for non-zero capacity. As a result, nothing
is done for default-constructed container.

Note that this patch also affects the QSet::squeeze() behavior, because
QSet uses QHash as its underlying data type.

Task-number: QTBUG-91736
Change-Id: Ib1c3c8b7b3de6ddeefea0e70b1ec71803e8fd3b3
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Andreas Buhr <andreas.buhr@qt.io>
(cherry picked from commit b095d268788343b67a3995db7148dcc3af9bde1a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Ivan Solovev 2021-07-23 14:08:33 +02:00 committed by Qt Cherry-pick Bot
parent d54f9df1bd
commit 448674a68d
3 changed files with 11 additions and 5 deletions
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6
src/corelib/tools/qhash.h
View File

@ -850,7 +850,11 @@ public:
else else
d = Data::detached(d, size_t(size)); d = Data::detached(d, size_t(size));
} }
inline void squeeze() { reserve(0); } inline void squeeze()
{
if (capacity())
reserve(0);
}
inline void detach() { if (!d || d->ref.isShared()) d = Data::detached(d); } inline void detach() { if (!d || d->ref.isShared()) d = Data::detached(d); }
inline bool isDetached() const noexcept { return d && !d->ref.isShared(); } inline bool isDetached() const noexcept { return d && !d->ref.isShared(); }

2
tests/auto/corelib/tools/qhash/tst_qhash.cpp
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@ -2587,6 +2587,8 @@ void tst_QHash::fineTuningInEmptyHash()
{ {
QHash<QString, int> hash; QHash<QString, int> hash;
QCOMPARE(hash.capacity(), 0); QCOMPARE(hash.capacity(), 0);
hash.squeeze();
QCOMPARE(hash.capacity(), 0);
QVERIFY(qFuzzyIsNull(hash.load_factor())); QVERIFY(qFuzzyIsNull(hash.load_factor()));
QVERIFY(!hash.isDetached()); QVERIFY(!hash.isDetached());

8
tests/auto/corelib/tools/qset/tst_qset.cpp
View File

@ -244,12 +244,12 @@ void tst_QSet::reserve()
void tst_QSet::squeeze() void tst_QSet::squeeze()
{ {
QSet<int> set; QSet<int> set;
int n = set.capacity(); QCOMPARE(set.capacity(), 0);
QVERIFY(n == 0);
set.squeeze(); set.squeeze();
n = set.capacity(); QCOMPARE(set.capacity(), 0);
QVERIFY(n > 0 && n < 100);
QVERIFY(!set.isDetached());
set.reserve(1000); set.reserve(1000);
QVERIFY(set.capacity() >= 1000); QVERIFY(set.capacity() >= 1000);