Wasm: Support event loop wakeup from secondary threads

Minimal fix for the missing wakeup issue, in leu of
a new event loop implementation.

So far, emscripten_async_run_in_main_runtime_thread_
looks to be our option for scheduling calls on the
main thread. This function is available on emsdk 1.38.22
and higher.

Requires making from QEventDispatcherUNIX::wakeUp()
non-final. The future event dispatcher implementation
will not inherit QEventDispatcherUNIX, so this is a
temporary change.

Fixes: QTBUG-75793
Task-number: QTBUG-76007
Change-Id: Ie6f6ee6f7674206fc0673a4fe866ac614432ab65
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

3 files changed, 26 insertions, 1 deletions

diff --git a/src/corelib/kernel/qeventdispatcher_unix_p.h b/src/corelib/kernel/qeventdispatcher_unix_p.h
index f37edfc967..581df9242c 100644
--- a/src/corelib/kernel/qeventdispatcher_unix_p.h
+++ b/src/corelib/kernel/qeventdispatcher_unix_p.h
@@ -118,7 +118,7 @@ public:
 
     int remainingTime(int timerId) final;
 
-    void wakeUp() final;
+    void wakeUp() override;
     void interrupt() final;
     void flush() override;
 
diff --git a/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp b/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp
index 41355d72ae..d89cd78b28 100644
--- a/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp
+++ b/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp
@@ -33,6 +33,14 @@
 
 #include <emscripten.h>
 
+#if (__EMSCRIPTEN_major__ > 1 || __EMSCRIPTEN_minor__ > 38 || __EMSCRIPTEN_minor__ == 38 && __EMSCRIPTEN_tiny__ >= 22)
+#  define EMSCRIPTEN_HAS_ASYNC_RUN_IN_MAIN_RUNTIME_THREAD
+#endif
+
+#ifdef EMSCRIPTEN_HAS_ASYNC_RUN_IN_MAIN_RUNTIME_THREAD
+#include <emscripten/threading.h>
+#endif
+
 class QWasmEventDispatcherPrivate : public QEventDispatcherUNIXPrivate
 {
 
@@ -179,3 +187,18 @@ void QWasmEventDispatcher::doMaintainTimers()
     emscripten_async_call(callback, this, toWaitDuration);
     m_currentTargetTime = newTargetTime;
 }
+
+void QWasmEventDispatcher::wakeUp()
+{
+#ifdef EMSCRIPTEN_HAS_ASYNC_RUN_IN_MAIN_RUNTIME_THREAD
+    if (!emscripten_is_main_runtime_thread())
+        emscripten_async_run_in_main_runtime_thread_(EM_FUNC_SIG_VI, (void*)(&QWasmEventDispatcher::mainThreadWakeUp), this);
+#endif
+    QEventDispatcherUNIX::wakeUp();
+}
+
+void QWasmEventDispatcher::mainThreadWakeUp(void *eventDispatcher)
+{
+    emscripten_resume_main_loop(); // Service possible requestUpdate Calls
+    static_cast<QWasmEventDispatcher *>(eventDispatcher)->processEvents(QEventLoop::AllEvents);
+}
diff --git a/src/plugins/platforms/wasm/qwasmeventdispatcher.h b/src/plugins/platforms/wasm/qwasmeventdispatcher.h
index 5300b3de73..f72d92ce07 100644
--- a/src/plugins/platforms/wasm/qwasmeventdispatcher.h
+++ b/src/plugins/platforms/wasm/qwasmeventdispatcher.h
@@ -51,6 +51,8 @@ public:
 protected:
     bool processEvents(QEventLoop::ProcessEventsFlags flags) override;
     void doMaintainTimers();
+    void wakeUp() override;
+    static void mainThreadWakeUp(void *eventDispatcher);
 
 private:
     bool m_hasMainLoop = false;