path: root/src/network
diff options
authorVolker Hilsheimer <>2019-07-24 15:05:23 +0200
committerVolker Hilsheimer <>2019-07-26 17:59:47 +0200
commite24a4976bebd7ca90deac2b40c08900625773a99 (patch)
tree222071dc7fbf1b8b17033109e35b3f8eb08f86ef /src/network
parente6498362fde937259295e9b2ddbe9b59136f47ba (diff)
QHostInfo: Always post results through the event loop to the receiver
Lookups performed via QHostInfoRunnable must not synchronously call the user-code's receiver objects, as that would execute user-code in the wrong thread. Instead, post a metacall event through the event loop of the receiver object, or the thread that initiated the lookup. This was done correctly for the trivial cases of empty host name or cached results, so the code generally existed. By moving it from a global function into a member function of QHostInfoResult, we can simply access the required data to construct and post the event. As we process that posted event, we need to check that the context object (which is already guarded via QPointer) is still alive, if we had one in the first place. If we had one, and it's deleted, then abort. [ChangeLog][QtNetwork][QHostInfo] Functors used in the lookupHost overloads are now called correctly in the thread of the context object. When used without context object, the thread that initiates the lookup will run the functor, and is required to run an event loop. Change-Id: I9b38d4f9a23cfc4d9e07bc72de2d2cefe5d0d033 Fixes: QTBUG-76276 Reviewed-by: Edward Welbourne <> Reviewed-by: MÃ¥rten Nordheim <>
Diffstat (limited to 'src/network')
2 files changed, 49 insertions, 10 deletions
diff --git a/src/network/kernel/qhostinfo.cpp b/src/network/kernel/qhostinfo.cpp
index 597c616fe9..7c82637564 100644
--- a/src/network/kernel/qhostinfo.cpp
+++ b/src/network/kernel/qhostinfo.cpp
@@ -106,11 +106,39 @@ int get_signal_index()
return signal_index + QMetaObjectPrivate::signalOffset(senderMetaObject);
-void emit_results_ready(const QHostInfo &hostInfo, const QObject *receiver,
- QtPrivate::QSlotObjectBase *slotObj)
+ The calling thread is likely the one that executes the lookup via
+ QHostInfoRunnable. Unless we operate with a queued connection already,
+ posts the QHostInfo to a dedicated QHostInfoResult object that lives in
+ the same thread as the user-provided receiver, or (if there is none) in
+ the thread that made the call to lookupHost. That QHostInfoResult object
+ then calls the user code in the correct thread.
+ The 'result' object deletes itself (via deleteLater) when the metacall
+ event is received.
+void QHostInfoResult::postResultsReady(const QHostInfo &info)
+ // queued connection will take care of dispatching to right thread
+ if (!slotObj) {
+ emitResultsReady(info);
+ return;
+ }
static const int signal_index = get_signal_index();
+ // we used to have a context object, but it's already destroyed
+ if (withContextObject && !receiver)
+ return;
+ /* QHostInfoResult c'tor moves the result object to the thread of receiver.
+ If we don't have a receiver, then the result object will not live in a
+ thread that runs an event loop - so move it to this' thread, which is the thread
+ that initiated the lookup, and required to have a running event loop. */
auto result = new QHostInfoResult(receiver, slotObj);
+ if (!receiver)
+ result->moveToThread(thread());
const int nargs = 2;
auto types = reinterpret_cast<int *>(malloc(nargs * sizeof(int)));
@@ -120,15 +148,13 @@ void emit_results_ready(const QHostInfo &hostInfo, const QObject *receiver,
auto args = reinterpret_cast<void **>(malloc(nargs * sizeof(void *)));
args[0] = 0;
- args[1] = QMetaType::create(types[1], &hostInfo);
+ args[1] = QMetaType::create(types[1], &info);
auto metaCallEvent = new QMetaCallEvent(slotObj, nullptr, signal_index, nargs, types, args);
qApp->postEvent(result, metaCallEvent);
\class QHostInfo
\brief The QHostInfo class provides static functions for host name lookups.
@@ -335,6 +361,10 @@ int QHostInfo::lookupHost(const QString &name, QObject *receiver,
ready, the \a functor is called with a QHostInfo argument. The
QHostInfo object can then be inspected to get the results of the
+ The \a functor will be run in the thread that makes the call to lookupHost;
+ that thread must have a running Qt event loop.
\note There is no guarantee on the order the signals will be emitted
if you start multiple requests with lookupHost().
@@ -632,7 +662,8 @@ int QHostInfo::lookupHostImpl(const QString &name,
QHostInfo hostInfo(id);
hostInfo.setErrorString(QCoreApplication::translate("QHostInfo", "No host name given"));
- emit_results_ready(hostInfo, receiver, slotObj);
+ QHostInfoResult result(receiver, slotObj);
+ result.postResultsReady(hostInfo);
return id;
@@ -646,7 +677,8 @@ int QHostInfo::lookupHostImpl(const QString &name,
QHostInfo info = manager->cache.get(name, &valid);
if (valid) {
- emit_results_ready(info, receiver, slotObj);
+ QHostInfoResult result(receiver, slotObj);
+ result.postResultsReady(info);
return id;
@@ -707,7 +739,7 @@ void QHostInfoRunnable::run()
// signal emission
- resultEmitter.emitResultsReady(hostInfo);
+ resultEmitter.postResultsReady(hostInfo);
#if QT_CONFIG(thread)
// now also iterate through the postponed ones
@@ -720,7 +752,7 @@ void QHostInfoRunnable::run()
QHostInfoRunnable* postponed = *it;
// we can now emit
- postponed->resultEmitter.emitResultsReady(hostInfo);
+ postponed->resultEmitter.postResultsReady(hostInfo);
delete postponed;
manager->postponedLookups.erase(partitionBegin, partitionEnd);
diff --git a/src/network/kernel/qhostinfo_p.h b/src/network/kernel/qhostinfo_p.h
index 8898d6ff50..bbf4cc36d1 100644
--- a/src/network/kernel/qhostinfo_p.h
+++ b/src/network/kernel/qhostinfo_p.h
@@ -84,12 +84,14 @@ class QHostInfoResult : public QObject
QPointer<const QObject> receiver = nullptr;
QtPrivate::QSlotObjectBase *slotObj = nullptr;
+ const bool withContextObject = false;
QHostInfoResult() = default;
QHostInfoResult(const QObject *receiver, QtPrivate::QSlotObjectBase *slotObj) :
- slotObj(slotObj)
+ slotObj(slotObj),
+ withContextObject(slotObj && receiver)
connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit, this,
@@ -97,10 +99,15 @@ public:
+ void postResultsReady(const QHostInfo &info);
public Q_SLOTS:
inline void emitResultsReady(const QHostInfo &info)
if (slotObj) {
+ // we used to have a context object, but it's already destroyed
+ if (withContextObject && !receiver)
+ return;
QHostInfo copy = info;
void *args[2] = { 0, reinterpret_cast<void *>(&copy) };
slotObj->call(const_cast<QObject*>(, args);