QThreadData: refactor current() now that it never returns null

Simplying the body of the function to rely less on the exception
handling too. The implementations for Unix and Windows are now literally
identical, but duplicated because they call different static functions

Change-Id: Ia14910a1c778ff5e606afffdabb8035e4603edda
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/corelib/thread/qthread.cpp

@@ -1119,9 +1119,9 @@ void QThread::setTerminationEnabled(bool)
 // No threads: so we can just use static variables
 Q_CONSTINIT static QThreadData *data = nullptr;
 
-QThreadData *QThreadData::current(bool createIfNecessary)
+QThreadData *QThreadData::current()
 {
-    if (!data && createIfNecessary) {
+    if (!data) {
         data = new QThreadData;
         data->thread = new QAdoptedThread(data);
     }

src/corelib/thread/qthread_p.h

@@ -308,7 +308,7 @@ public:
     }
     ~QThreadData();
 
-    static Q_AUTOTEST_EXPORT QThreadData *current(bool createIfNecessary = true);
+    static Q_AUTOTEST_EXPORT QThreadData *current();
     static void clearCurrentThreadData();
     static QThreadData *get2(QThread *thread)
     { Q_ASSERT_X(thread != nullptr, "QThread", "internal error"); return thread->d_func()->data; }

src/corelib/thread/qthread_unix.cpp

@@ -124,7 +124,6 @@ int pthread_timedjoin_np(...) { return ENOSYS; }    // pretend
 // https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/libcxxabi/src/cxa_thread_atexit.cpp#L118-L120
 #endif // QT_CONFIG(broken_threadlocal_dtors)
 
-// Always access this through the {get,set,clear}_thread_data() functions.
 Q_CONSTINIT static thread_local QThreadData *currentThreadData = nullptr;
 
 static void destroy_current_thread_data(void *p)
@@ -176,13 +175,13 @@ static void destroy_main_thread_data()
 Q_DESTRUCTOR_FUNCTION(destroy_main_thread_data)
 #endif
 
-static void set_thread_data(QThreadData *data)
+static void set_thread_data(QThreadData *data) noexcept
 {
     if (data) {
         if constexpr (QT_CONFIG(broken_threadlocal_dtors)) {
             static pthread_key_t tls_key;
             struct TlsKey {
-                TlsKey() { pthread_key_create(&tls_key, destroy_current_thread_data); }
+                TlsKey() noexcept { pthread_key_create(&tls_key, destroy_current_thread_data); }
                 ~TlsKey() { pthread_key_delete(tls_key); }
             };
             static TlsKey currentThreadCleanup;
@@ -197,11 +196,6 @@ static void set_thread_data(QThreadData *data)
     currentThreadData = data;
 }
 
-static void clear_thread_data()
-{
-    set_thread_data(nullptr);
-}
-
 template <typename T>
 static typename std::enable_if<std::is_integral_v<T>, Qt::HANDLE>::type to_HANDLE(T id)
 {
@@ -228,28 +222,29 @@ static typename std::enable_if<std::is_pointer_v<T>, T>::type from_HANDLE(Qt::HA
 
 void QThreadData::clearCurrentThreadData()
 {
-    clear_thread_data();
+    set_thread_data(nullptr);
 }
 
-QThreadData *QThreadData::current(bool createIfNecessary)
+QThreadData *QThreadData::current()
 {
-    QThreadData *data = get_thread_data();
+    if (QThreadData *data = get_thread_data(); Q_LIKELY(data))
-    if (!data && createIfNecessary) {
+        return data;
-        data = new QThreadData;
+
+    std::unique_ptr data = std::make_unique<QThreadData>();
+
+    // This needs to be called prior to new QAdoptedThread() to avoid
+    // recursion (see qobject.cpp).
+    set_thread_data(data.get());
+
     QT_TRY {
-            set_thread_data(data);
+        data->thread.storeRelease(new QAdoptedThread(data.get()));
-            data->thread.storeRelease(new QAdoptedThread(data));
     } QT_CATCH(...) {
-            clear_thread_data();
+        clearCurrentThreadData();
-            data->deref();
-            data = nullptr;
         QT_RETHROW;
     }
-    }
+    return data.release();
-    return data;
 }
 
-
 void QAdoptedThread::init()
 {
 }

src/corelib/thread/qthread_win.cpp

@@ -72,7 +72,12 @@ static void destroy_current_thread_data(void *p)
     currentThreadData = nullptr;
 }
 
-static void set_thread_data(QThreadData *data)
+static QThreadData *get_thread_data()
+{
+    return currentThreadData;
+}
+
+static void set_thread_data(QThreadData *data) noexcept
 {
     if (data) {
         struct Cleanup {
@@ -91,24 +96,24 @@ void QThreadData::clearCurrentThreadData()
     set_thread_data(nullptr);
 }
 
-QThreadData *QThreadData::current(bool createIfNecessary)
+QThreadData *QThreadData::current()
 {
-    QThreadData *threadData = currentThreadData;
+    if (QThreadData *data = get_thread_data(); Q_LIKELY(data))
-    if (!threadData && createIfNecessary) {
+        return data;
-        threadData = new QThreadData;
+
-        // This needs to be called prior to new AdoptedThread() to
+    std::unique_ptr data = std::make_unique<QThreadData>();
-        // avoid recursion.
+
-        set_thread_data(threadData);
+    // This needs to be called prior to new QAdoptedThread() to avoid
+    // recursion (see qobject.cpp).
+    set_thread_data(data.get());
+
     QT_TRY {
-            threadData->thread.storeRelease(new QAdoptedThread(threadData));
+        data->thread.storeRelease(new QAdoptedThread(data.get()));
     } QT_CATCH(...) {
-            set_thread_data(nullptr);
+        clearCurrentThreadData();
-            threadData->deref();
-            threadData = 0;
         QT_RETHROW;
     }
-    }
+    return data.release();
-    return threadData;
 }
 
 void QAdoptedThread::init()