diff options
| author | Thiago Macieira <thiago.macieira@intel.com> | 2025-02-08 14:33:27 -0800 |
|---|---|---|
| committer | Thiago Macieira <thiago.macieira@intel.com> | 2025-03-31 17:04:13 -0400 |
| commit | 4afd089612448ae13136e287ced134c71499cfec (patch) | |
| tree | 0215f40365e84069243c55547fdf78508c3c148b /src/corelib/io/qloggingregistry.cpp | |
| parent | 51c8c0695192677f821759b98f8ba6496df41fa7 (diff) | |
QLoggingCategory: make defaultCategory() truly a global static
We don't need two independent Q_GLOBAL_STATIC variables: one for the
default category and the other for the logging registry. We can simply
save one in the other.
However, we can do better than even that. QLoggingCategory currently
doesn't hold any allocated resources: the const char *name points to a
static string and the void *d is always null. That means the constructor
and destructor only serve to register and unregister the category with
QLoggingRegistry, so we transfer that responsibility to QLoggingRegistry
itself (the un-registering is implicit in the registry's own
destruction).
The benefit of this is that the default QLoggingCategory can never be
found in a destroyed state, however late user code may be running after
::exit() was called. We have had a number of these issues of
De-Initialization Order Fiasco, especially since the changes to
QThreadData destruction timing.
Pick-to: 6.9
Change-Id: I2b6ea597ac257837669afffde2684c7b44a42e92
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Diffstat (limited to 'src/corelib/io/qloggingregistry.cpp')
| -rw-r--r-- | src/corelib/io/qloggingregistry.cpp | 23 |
1 files changed, 22 insertions, 1 deletions
diff --git a/src/corelib/io/qloggingregistry.cpp b/src/corelib/io/qloggingregistry.cpp index da8ed80ff16..ece58cfa87e 100644 --- a/src/corelib/io/qloggingregistry.cpp +++ b/src/corelib/io/qloggingregistry.cpp @@ -27,6 +27,7 @@ QT_BEGIN_NAMESPACE using namespace Qt::StringLiterals; Q_GLOBAL_STATIC(QLoggingRegistry, qtLoggingRegistry) +alignas(QLoggingCategory) static unsigned char defaultLoggingCategory[sizeof(QLoggingCategory)]; /*! \internal @@ -227,6 +228,14 @@ void QLoggingSettingsParser::parseNextLine(QStringView line) QLoggingRegistry::QLoggingRegistry() : categoryFilter(defaultCategoryFilter) { + using U = QLoggingCategory::UnregisteredInitialization; + Q_ASSERT_X(!self, "QLoggingRegistry", "Singleton recreated"); + self = this; + + // can't use std::construct_at here - private constructor + auto cat = new (defaultLoggingCategory) QLoggingCategory(U{}, defaultCategoryName); + categories.emplace(cat, QtDebugMsg); + #if defined(Q_OS_ANDROID) // Unless QCoreApplication has been constructed we can't be sure that // we are on Qt's main thread. If we did allow logging here, we would @@ -424,6 +433,18 @@ QLoggingRegistry *QLoggingRegistry::instance() return qtLoggingRegistry(); } +QLoggingCategory *QLoggingRegistry::defaultCategory() +{ + // Initialize the defaultLoggingCategory global static, if necessary. Note + // how it remains initialized forever, even if the QLoggingRegistry + // instance() is destroyed. + instance(); + + // std::launder() to be on the safe side, but it's unnecessary because the + // object is never recreated. + return std::launder(reinterpret_cast<QLoggingCategory *>(defaultLoggingCategory)); +} + /*! \internal Updates category settings according to rules. @@ -432,7 +453,7 @@ QLoggingRegistry *QLoggingRegistry::instance() */ void QLoggingRegistry::defaultCategoryFilter(QLoggingCategory *cat) { - const QLoggingRegistry *reg = QLoggingRegistry::instance(); + const QLoggingRegistry *reg = self; Q_ASSERT(reg->categories.contains(cat)); QtMsgType enableForLevel = reg->categories.value(cat); |