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QCache: fix updating entries breaking the internal chain

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After f08492c6fd9818c7d80b1725355453e179b4d85b was
merged this bug would manifest as an entry appearing twice
in the chain when a updating an existing entry (insert with
an existing key). This could sometimes result in crashes later
as the list filled up and the list was used in trim() to remove
various entries.

Fixes: QTBUG-89176
Change-Id: Ide80160fb4317dc0aefe79eec5dce7ec6813e790
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 0ca46358321f2244386b0b6558a915cda8c6c006)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Mårten Nordheim 2020-12-08 15:47:47 +01:00 committed by Qt Cherry-pick Bot
parent a0d963f436
commit b97001aa1c
2 changed files with 22 additions and 4 deletions
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9
src/corelib/tools/qcache.h
View File

@ -247,14 +247,15 @@ public:
if (result.initialized) {
cost -= n->value.cost;
result.it.node()->emplace(object, cost);
relink(key);
} else {
Node::createInPlace(n, key, object, cost);
n->prev = &chain;
n->next = chain.next;
chain.next->prev = n;
chain.next = n;
}
total += cost;
n->prev = &chain;
n->next = chain.next;
chain.next->prev = n;
chain.next = n;
return true;
}
T *object(const Key &key) const noexcept

17
tests/auto/corelib/tools/qcache/tst_qcache.cpp
View File

@ -48,6 +48,7 @@ private slots:
void take();
void axioms_on_key_type();
void largeCache();
void internalChainOrderAfterEntryUpdate();
};
@ -414,5 +415,21 @@ void tst_QCache::largeCache()
QVERIFY(cache.size() == 0);
}
// The internal chain could lose track of some objects.
// Make sure it doesn't happen again.
void tst_QCache::internalChainOrderAfterEntryUpdate()
{
QCache<QString, int> cache;
cache.setMaxCost(20);
cache.insert(QString::number(1), new int, 1);
cache.insert(QString::number(2), new int, 1);
cache.insert(QString::number(1), new int, 1);
// If the chain is still 'in order' then setting maxCost == 0 should
// a. not crash, and
// b. remove all the elements in the QHash
cache.setMaxCost(0);
QCOMPARE(cache.size(), 0);
}
QTEST_APPLESS_MAIN(tst_QCache)
#include "tst_qcache.moc"