QTimer: do not set active state when setting a negative interval

QObject::startTimer() returns 0 in case of failure, for example when
someone tries to register a timer with a negative interval.

However, QTimer internally uses -1 as an invalid timer id.
This could lead to a situation when the timer was not really started,
but QTimer::isActive() returned true.

This patch fixes it in two ways:
- check the return value of QObject::startTimer() and treat 0 as an
  error.
- do not treat 0 as a valid timer id when calculating the active state.

As a drive-by: move the `using namespace std::chrono_literals;`
declaration to the top of tst_qtimer.cpp, so that we do not need to
repeat it in each test case.

Fixes: QTBUG-122087
Pick-to: 6.7 6.6 6.5
Change-Id: I0e21152b2173ebb5fb0dada1b99a903a321ca9c4
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/src/corelib/kernel/qtimer.cpp b/src/corelib/kernel/qtimer.cpp
index 90f6dacd42..04e32d9ec7 100644
--- a/src/corelib/kernel/qtimer.cpp
+++ b/src/corelib/kernel/qtimer.cpp
@@ -192,8 +192,11 @@ void QTimer::start()
     Q_D(QTimer);
     if (d->id != QTimerPrivate::INV_TIMER) // stop running timer
         stop();
-    d->id = QObject::startTimer(std::chrono::milliseconds{d->inter}, d->type);
-    d->isActiveData.notify();
+    const int id = QObject::startTimer(std::chrono::milliseconds{d->inter}, d->type);
+    if (id > 0) {
+        d->id = id;
+        d->isActiveData.notify();
+    }
 }
 
 /*!
@@ -554,9 +557,16 @@ void QTimer::setInterval(int msec)
     d->inter.setValueBypassingBindings(msec);
     if (d->id != QTimerPrivate::INV_TIMER) { // create new timer
         QObject::killTimer(d->id);                        // restart timer
-        d->id = QObject::startTimer(std::chrono::milliseconds{msec}, d->type);
-        // No need to call markDirty() for d->isActiveData here,
-        // as timer state actually does not change
+        const int id = QObject::startTimer(std::chrono::milliseconds{msec}, d->type);
+        if (id > 0) {
+            // Restarted successfully. No need to update the active state.
+            d->id = id;
+        } else {
+            // Failed to start the timer.
+            // Need to notify about active state change.
+            d->id = QTimerPrivate::INV_TIMER;
+            d->isActiveData.notify();
+        }
     }
     if (intervalChanged)
         d->inter.notify();