Fix logging after static destructors have run

Before we could either crash or end up in an infinite loop (*) when
somebody logged after the static QThreadStorage in the
colorLogToStderr() had been destructed.

(*) QThreadStorageData::finish() can potential log on errors, which
reallocted the outBuffers, which messed up the tls list, which led
to finish() deleting the buffers and then logging yet another error...

[this is for 6.6/6.5 only - 6.7 gets a similar, but simpler fix]

Change-Id: I47f0b403b214b42e3b68f5ecc4776fa6aaba0cfc
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Thomas Senyk <thomas.senyk@qt.io>
(cherry picked from commit 840a9b43704ad8e32af18297bba207667dfa815a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/src/common-lib/logging.cpp b/src/common-lib/logging.cpp
index 55f4077f..a8138426 100644
--- a/src/common-lib/logging.cpp
+++ b/src/common-lib/logging.cpp
@@ -174,6 +174,9 @@ struct LoggingGlobal
     QMutex deferredMessagesMutex;
     std::vector<DeferredMessage> deferredMessages;
 
+    // Try to re-use a 512 byte buffer per thread as much as possible to avoid allocations.
+    QThreadStorage<QByteArray> outBuffers;
+
     ~LoggingGlobal();
 };
 
@@ -215,9 +218,7 @@ static void colorLogToStderr(QtMsgType msgType, const QMessageLogContext &contex
     if (msgType < QtDebugMsg || msgType > QtInfoMsg)
         msgType = QtCriticalMsg;
 
-    // Try to re-use a 512 byte buffer per thread as much as possible to avoid allocations.
-    static QThreadStorage<QByteArray> outBuffers;
-    QByteArray &out = outBuffers.localData();
+    QByteArray &out = lg()->outBuffers.localData();
     if (out.capacity() > 512)
         out.clear();
     if (!out.capacity())
@@ -395,6 +396,10 @@ LoggingGlobal::~LoggingGlobal()
     // we do an unnecessary (but cheap) qInstallMessageHandler() at program exit, but this way
     // we cannot forget to dump the deferred messages whenever we exit
     Logging::completeSetup();
+
+    // we are dead now, so make sure that anyone logging after this point will not crash the program
+    if (defaultQtHandler)
+        qInstallMessageHandler(defaultQtHandler);
 }
 
 QStringList Logging::filterRules()