From 088b364e4b220ffe3acf28842444c6a80601f2bb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Morten=20Johan=20S=C3=B8rvig?= <morten.sorvig@qt.io>
Date: Mon, 13 Sep 2021 11:09:48 +0200
Subject: [PATCH] QEventDispatcherWasm: handle EventLoopExec
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Call emscripten_set_main_loop like the old GUI event
dispatcher did, with one difference that requestAnimationFrame
updates are now no longer handled by the event dispatcher.

Change-Id: If02d90ae9c45d7b38999567d733a237af842cded
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
---
 src/corelib/kernel/qeventdispatcher_wasm.cpp | 18 ++++++++++++++++++
 src/corelib/kernel/qeventdispatcher_wasm_p.h |  1 +
 2 files changed, 19 insertions(+)

diff --git a/src/corelib/kernel/qeventdispatcher_wasm.cpp b/src/corelib/kernel/qeventdispatcher_wasm.cpp
index 61b49fdc551..7632b2ca55b 100644
--- a/src/corelib/kernel/qeventdispatcher_wasm.cpp
+++ b/src/corelib/kernel/qeventdispatcher_wasm.cpp
@@ -208,6 +208,8 @@ bool QEventDispatcherWasm::processEvents(QEventLoop::ProcessEventsFlags flags)
 
     if (flags & QEventLoop::DialogExec)
         handleDialogExec();
+    else if (flags & QEventLoop::EventLoopExec)
+        handleEventLoopExec();
 
     if (!(flags & QEventLoop::ExcludeUserInputEvents))
         pollForNativeEvents();
@@ -364,6 +366,22 @@ void QEventDispatcherWasm::wakeUp()
     emscripten_async_call(&QEventDispatcherWasm::callProcessEvents, this, 0);
 }
 
+void QEventDispatcherWasm::handleEventLoopExec()
+{
+    // Start the main loop, and then stop it on the first callback. This
+    // is done for the "simulateInfiniteLoop" functionality where
+    // emscripten_set_main_loop() throws a JS exception which returns
+    // control to the browser while preserving the C++ stack.
+    //
+    // Note that we don't use asyncify here: Emscripten supports one level of
+    // asyncify only and we want to reserve that for dialog exec() instead of
+    // using it for the one qApp exec().
+    const bool simulateInfiniteLoop = true;
+    emscripten_set_main_loop([](){
+        emscripten_pause_main_loop();
+    }, 0, simulateInfiniteLoop);
+}
+
 void QEventDispatcherWasm::handleDialogExec()
 {
 #if !QT_HAVE_EMSCRIPTEN_ASYNCIFY
diff --git a/src/corelib/kernel/qeventdispatcher_wasm_p.h b/src/corelib/kernel/qeventdispatcher_wasm_p.h
index 75db11723c4..7eea28b0523 100644
--- a/src/corelib/kernel/qeventdispatcher_wasm_p.h
+++ b/src/corelib/kernel/qeventdispatcher_wasm_p.h
@@ -90,6 +90,7 @@ private:
     bool isMainThreadEventDispatcher();
     bool isSecondaryThreadEventDispatcher();
 
+    void handleEventLoopExec();
     void handleDialogExec();
     void pollForNativeEvents();
     bool waitForForEvents();