wasm: Proxy emscripten_fetch() to the main thread

Calling emscripten_fetch() on worker thread which never yields control
back to the browser, will leave the fetch request pending forever.
This can be a problematic for example in QML Loader, which tries
to load resource by network.
Proxy this function call to the main thread, so it can be processed by
the browser.

Fixes: QTBUG-118225
Pick-to: 6.6 6.5
Change-Id: I969d73f6a66670c4135960e08d2eedc8d2a6e5c3
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

src/corelib/kernel/qeventdispatcher_wasm_p.h

@@ -53,6 +53,7 @@ public:
     void interrupt() override;
     void wakeUp() override;
 
+    static void runOnMainThreadAsync(std::function<void(void)> fn);
     static void socketSelect(int timeout, int socket, bool waitForRead, bool waitForWrite,
                             bool *selectForRead, bool *selectForWrite, bool *socketDisconnect);
 protected:
@@ -90,7 +91,6 @@ private:
     static void run(std::function<void(void)> fn);
     static void runOnMainThread(std::function<void(void)> fn);
     static void runAsync(std::function<void(void)> fn);
-    static void runOnMainThreadAsync(std::function<void(void)> fn);
 
     static QEventDispatcherWasm *g_mainThreadEventDispatcher;
 

src/network/access/qnetworkreplywasmimpl.cpp

@@ -9,6 +9,7 @@
 #include <QtCore/qcoreapplication.h>
 #include <QtCore/qfileinfo.h>
 #include <QtCore/qthread.h>
+#include <QtCore/private/qeventdispatcher_wasm_p.h>
 #include <QtCore/private/qoffsetstringarray_p.h>
 #include <QtCore/private/qtools_p.h>
 
@@ -295,7 +296,10 @@ void QNetworkReplyWasmImplPrivate::doSendRequest()
     QByteArray destinationPath = dPath.toUtf8();
     attr.destinationPath = destinationPath.constData();
 
-    m_fetch = emscripten_fetch(&attr, request.url().toString().toUtf8());
+    auto url = request.url().toString().toUtf8();
+    QEventDispatcherWasm::runOnMainThreadAsync([attr, url]() mutable {
+        emscripten_fetch(&attr, url);
+    });
     state = Working;
 }