Move runTaskOnMainThread to qstdweb_p.h, use it in WASM dispatcher

This unifies the approach to running sync tasks (possibly with a
return value) on the main thread.

Change-Id: I2a05c4f40115a79dbf03c03fa8d8db34124884dc
Reviewed-by: Mikołaj Boc <Mikolaj.Boc@qt.io>

src/corelib/kernel/qeventdispatcher_wasm.cpp

@@ -16,6 +16,12 @@
 
 using namespace std::chrono_literals;
 
+#if QT_CONFIG(thread)
+#define PROXYING_QUEUE_PARAM , &g_proxyingQueue
+#else
+#define PROXYING_QUEUE_PARAM
+#endif  // QT_CONFIG(thread)
+
 QT_BEGIN_NAMESPACE
 
 // using namespace emscripten;
@@ -315,8 +321,10 @@ void QEventDispatcherWasm::registerSocketNotifier(QSocketNotifier *notifier)
 
     bool wasEmpty = g_socketNotifiers.empty();
     g_socketNotifiers.insert({notifier->socket(), notifier});
-    if (wasEmpty)
-        runOnMainThread([]{ setEmscriptenSocketCallbacks(); });
+    if (wasEmpty) {
+        qstdweb::runTaskOnMainThread<void>([] { setEmscriptenSocketCallbacks(); }
+                                           PROXYING_QUEUE_PARAM);
+    }
 }
 
 void QEventDispatcherWasm::unregisterSocketNotifier(QSocketNotifier *notifier)
@@ -331,8 +339,10 @@ void QEventDispatcherWasm::unregisterSocketNotifier(QSocketNotifier *notifier)
         }
     }
 
-    if (g_socketNotifiers.empty())
-        runOnMainThread([]{ clearEmscriptenSocketCallbacks(); });
+    if (g_socketNotifiers.empty()) {
+        qstdweb::runTaskOnMainThread<void>([] { clearEmscriptenSocketCallbacks(); }
+                                           PROXYING_QUEUE_PARAM);
+    }
 }
 
 void QEventDispatcherWasm::registerTimer(int timerId, qint64 interval, Qt::TimerType timerType, QObject *object)
@@ -528,14 +538,16 @@ bool QEventDispatcherWasm::wakeEventDispatcherThread()
     if (useJspi()) {
         if (!qt_jspi_can_resume_js())
             return false;
-        runOnMainThread([]{ qt_jspi_resume_js(); });
+        return qstdweb::runTaskOnMainThread<bool>([]() { return qt_jspi_resume_js(); }
+                                                  PROXYING_QUEUE_PARAM);
+    }
+    return g_is_asyncify_suspended
+            && qstdweb::runTaskOnMainThread<bool>(
+                    [] {
+                        qt_asyncify_resume();
                         return true;
                     }
-    if (g_is_asyncify_suspended) {
-        runOnMainThread([]{ qt_asyncify_resume(); });
-        return true;
-    }
-    return false;
+                    PROXYING_QUEUE_PARAM);
 }
 
 // Process event activation callbacks for the main thread event dispatcher.
@@ -620,7 +632,8 @@ void QEventDispatcherWasm::updateNativeTimer()
 
     // Update the native timer for this thread/dispatcher. This must be
     // done on the main thread where we have access to native API.
-    runOnMainThread([this, maintainNativeTimer]() {
+    qstdweb::runTaskOnMainThread<void>(
+            [this, maintainNativeTimer]() {
                 Q_ASSERT(emscripten_is_main_runtime_thread());
 
                 // "this" may have been deleted, or may be about to be deleted.
@@ -630,7 +643,8 @@ void QEventDispatcherWasm::updateNativeTimer()
                 LOCK_GUARD(g_staticDataMutex);
                 if (isValidEventDispatcherPointer(this))
                     maintainNativeTimer();
-    });
+            }
+            PROXYING_QUEUE_PARAM);
 }
 
 // Static timer activation callback. Must be called on the main thread
@@ -896,22 +910,6 @@ void QEventDispatcherWasm::runAsync(std::function<void(void)> fn)
     trampoline(new std::function<void(void)>(fn));
 }
 
-// Runs a function on the main thread. The function runs synchronusly if
-// the calling thread is then main thread.
-void QEventDispatcherWasm::runOnMainThread(std::function<void(void)> fn)
-{
-#if QT_CONFIG(thread)
-    if (!emscripten_is_main_runtime_thread()) {
-        void *context = new std::function<void(void)>(fn);
-        g_proxyingQueue.proxyAsync(g_mainThread, [context]{
-            trampoline(context);
-        });
-        return;
-    }
-#endif
-    fn();
-}
-
 // Runs a function on the main thread. The function always runs asynchronously,
 // also if the calling thread is the main thread.
 void QEventDispatcherWasm::runOnMainThreadAsync(std::function<void(void)> fn)

src/corelib/kernel/qeventdispatcher_wasm_p.h

@@ -89,7 +89,6 @@ private:
 
     static void run(std::function<void(void)> fn);
     static void runAsync(std::function<void(void)> fn);
-    static void runOnMainThread(std::function<void(void)> fn);
     static void runOnMainThreadAsync(std::function<void(void)> fn);
 
     static QEventDispatcherWasm *g_mainThreadEventDispatcher;

src/corelib/platform/wasm/qstdweb_p.h

@@ -28,6 +28,11 @@
 #include <string>
 #include <utility>
 
+#if QT_CONFIG(thread)
+#include <emscripten/proxying.h>
+#include <emscripten/threading.h>
+#endif  // #if QT_CONFIG(thread)
+
 QT_BEGIN_NAMESPACE
 
 class QMimeData;
@@ -218,6 +223,43 @@ namespace qstdweb {
     Q_CORE_EXPORT std::shared_ptr<CancellationFlag>
     readDataTransfer(emscripten::val webObject, std::function<QVariant(QByteArray)> imageReader,
                      std::function<void(std::unique_ptr<QMimeData>)> onDone);
+
+#if QT_CONFIG(thread)
+    template<class T>
+    T proxyCall(std::function<T()> task, emscripten::ProxyingQueue *queue)
+    {
+        T result;
+        queue->proxySync(emscripten_main_browser_thread_id(),
+                         [task, result = &result]() { *result = task(); });
+        return result;
+    }
+
+    template<>
+    inline void proxyCall<void>(std::function<void()> task, emscripten::ProxyingQueue *queue)
+    {
+        queue->proxySync(emscripten_main_browser_thread_id(), task);
+    }
+
+    template<class T>
+    T runTaskOnMainThread(std::function<T()> task, emscripten::ProxyingQueue *queue)
+    {
+        return emscripten_is_main_runtime_thread() ? task() : proxyCall<T>(std::move(task), queue);
+    }
+
+    template<class T>
+    T runTaskOnMainThread(std::function<T()> task)
+    {
+        emscripten::ProxyingQueue singleUseQueue;
+        return runTaskOnMainThread<T>(task, &singleUseQueue);
+    }
+
+#else
+    template<class T>
+    T runTaskOnMainThread(std::function<T()> task)
+    {
+        return task();
+    }
+#endif // QT_CONFIG(thread)
 }
 
 QT_END_NAMESPACE