diff options
authorMarc Mutz <>2019-07-04 15:24:13 +0200
committerMarc Mutz <>2019-07-09 13:09:24 +0000
commit0a3107dd302c521c240b273229ba40a358cb0873 (patch)
parent1c6828b9d61a5988e91e67342cc0f616fa87949e (diff)
QHostInfo: fix a race condition on QHostInfoCache::enabled
In auto-test-enabled builds, QHostInfoCache can be enabled and disabled using qt_qhostinfo_enable_cache() at any time. We cannot rule out that users use this function, or, indeed, that the auto-test never gets a threading stress-test. Under the assumption, then, that QHostInfoCache::enabled can be set by any thread at any time, and is read by any thread using QHostInfo::lookupHost(), we're presented with a data race, thus UB. Fix by making the accesses to QHostInfoCache::enabed atomic. Relaxed operations are suffcient, as the bool is the only data of interest in these situations. In particular, access to the cache itself is protected by the cache's mutex. We use std::atomic<bool> because QAtomicInteger<bool> doesn't exist on all implementations, but std::atomic<bool> must. Commit a0faf9e2366 set the precedent that it works. Change-Id: Ia1766753bb54c5fe8d8447b51a49a96a7a853eef Reviewed-by: MÃ¥rten Nordheim <>
2 files changed, 7 insertions, 17 deletions
diff --git a/src/network/kernel/qhostinfo.cpp b/src/network/kernel/qhostinfo.cpp
index e9ea6335d2..597c616fe9 100644
--- a/src/network/kernel/qhostinfo.cpp
+++ b/src/network/kernel/qhostinfo.cpp
@@ -952,23 +952,10 @@ void qt_qhostinfo_cache_inject(const QString &hostname, const QHostInfo &resolut
QHostInfoCache::QHostInfoCache() : max_age(60), enabled(true), cache(128)
- enabled = false;
+, std::memory_order_relaxed);
-bool QHostInfoCache::isEnabled()
- return enabled;
-// this function is currently only used for the auto tests
-// and not usable by public API
-void QHostInfoCache::setEnabled(bool e)
- enabled = e;
QHostInfo QHostInfoCache::get(const QString &name, bool *valid)
QMutexLocker locker(&this->mutex);
diff --git a/src/network/kernel/qhostinfo_p.h b/src/network/kernel/qhostinfo_p.h
index 8cce302166..8898d6ff50 100644
--- a/src/network/kernel/qhostinfo_p.h
+++ b/src/network/kernel/qhostinfo_p.h
@@ -73,6 +73,7 @@
#include <QNetworkSession>
#include <QSharedPointer>
+#include <atomic>
@@ -176,10 +177,12 @@ public:
void put(const QString &name, const QHostInfo &info);
void clear();
- bool isEnabled();
- void setEnabled(bool e);
+ bool isEnabled() { return enabled.load(std::memory_order_relaxed); }
+ // this function is currently only used for the auto tests
+ // and not usable by public API
+ void setEnabled(bool e) {, std::memory_order_relaxed); }
- bool enabled;
+ std::atomic<bool> enabled;
struct QHostInfoCacheElement {
QHostInfo info;
QElapsedTimer age;