wasm: include asyncify support unconditionally

Emscripten's option for enabling asyncify (-sASYNCIFY) is a link-time
option, which means there is no requirement to have a separate asyncify
build, at least for static builds.

Replace the current QT_HAVE_EMSCRIPTEN_ASYNCIFY compile-time option
with a run-time option which checks if the asyncify API is available.

Keep support for configuring with "-device-option QT_EMSCRIPTEN_ASYNCIFY=1"
for backwards compatibility and for the use case where want asyncify
support to be on by default for a given Qt build.

Enable asyncify for the asyncify_exec example.

Pick-to: 6.4
Change-Id: I301fd7e2d3c0367532c886f4e34b23e1093646ad
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

cmake/QtWasmHelpers.cmake

@@ -75,9 +75,13 @@ function (qt_internal_setup_wasm_target_properties wasmTarget)
         set(QT_CFLAGS_OPTIMIZE_DEBUG "-Os" CACHE STRING INTERNAL FORCE)
         set(QT_FEATURE_optimize_debug ON CACHE BOOL INTERNAL FORCE)
 
-        target_link_options("${wasmTarget}" INTERFACE "SHELL:-s ASYNCIFY" "-Os" "-s" "ASYNCIFY_IMPORTS=[qt_asyncify_suspend_js, qt_asyncify_resume_js]")
+        target_link_options("${wasmTarget}" INTERFACE "SHELL:-s ASYNCIFY" "-Os")
         target_compile_definitions("${wasmTarget}" INTERFACE QT_HAVE_EMSCRIPTEN_ASYNCIFY)
     endif()
+
+    #  Set ASYNCIFY_IMPORTS unconditionally in order to support enabling asyncify at link time.
+    target_link_options("${wasmTarget}" INTERFACE "SHELL:-sASYNCIFY_IMPORTS=qt_asyncify_suspend_js,qt_asyncify_resume_js")
+
 endfunction()
 
 function(qt_internal_wasm_add_finalizers target)

mkspecs/wasm-emscripten/qmake.conf

@@ -22,12 +22,12 @@ load(emcc_ver)
         # (with "wasm validation error: too many locals" type errors) if optimizations
         # are omitted. Enable optimizations also for debug builds.
         QMAKE_LFLAGS_DEBUG  += -Os
-
-        # Declare all async functions
-        QMAKE_LFLAGS += -s \'ASYNCIFY_IMPORTS=[\"qt_asyncify_suspend_js\", \"qt_asyncify_resume_js\", \"emscripten_sleep\"]\'
     }
 }
 
+# Declare async functions
+QMAKE_LFLAGS += -s \'ASYNCIFY_IMPORTS=qt_asyncify_suspend_js,qt_asyncify_resume_js\'
+
 EMCC_COMMON_LFLAGS += \
     -s WASM=1 \
     -s MAX_WEBGL_VERSION=2 \

src/corelib/kernel/qeventdispatcher_wasm.cpp

@@ -26,14 +26,16 @@ Q_LOGGING_CATEGORY(lcEventDispatcherTimers, "qt.eventdispatcher.timers");
 #define LOCK_GUARD(M)
 #endif
 
-#ifdef QT_HAVE_EMSCRIPTEN_ASYNCIFY
-
 // Emscripten asyncify currently supports one level of suspend -
 // recursion is not permitted. We track the suspend state here
 // on order to fail (more) gracefully, but we can of course only
 // track Qts own usage of asyncify.
 static bool g_is_asyncify_suspended = false;
 
+EM_JS(bool, qt_have_asyncify_js, (), {
+    return typeof Asyncify != "undefined";
+});
+
 EM_JS(void, qt_asyncify_suspend_js, (), {
     let sleepFn = (wakeUp) => {
         Module.qtAsyncifyWakeUp = wakeUp;
@@ -52,6 +54,15 @@ EM_JS(void, qt_asyncify_resume_js, (), {
     setTimeout(wakeUp);
 });
 
+// Returns true if asyncify is available.
+bool qt_have_asyncify()
+{
+    static bool have_asyncify = []{
+        return qt_have_asyncify_js();
+    }();
+    return have_asyncify;
+}
+
 // Suspends the main thread until qt_asyncify_resume() is called. Returns
 // false immediately if Qt has already suspended the main thread (recursive
 // suspend is not supported by Emscripten). Returns true (after resuming),
@@ -76,8 +87,6 @@ bool qt_asyncify_resume()
     return true;
 }
 
-#endif // QT_HAVE_EMSCRIPTEN_ASYNCIFY
-
 Q_CONSTINIT QEventDispatcherWasm *QEventDispatcherWasm::g_mainThreadEventDispatcher = nullptr;
 #if QT_CONFIG(thread)
 Q_CONSTINIT QVector<QEventDispatcherWasm *> QEventDispatcherWasm::g_secondaryThreadEventDispatchers;
@@ -359,16 +368,15 @@ void QEventDispatcherWasm::handleApplicationExec()
 
 void QEventDispatcherWasm::handleDialogExec()
 {
-#ifndef QT_HAVE_EMSCRIPTEN_ASYNCIFY
+    if (!qt_have_asyncify()) {
         qWarning() << "Warning: dialog exec() is not supported on Qt for WebAssembly in this"
                    << "configuration. Please use show() instead, or enable experimental support"
                    << "for asyncify.\n"
                    << "When using exec() (without asyncify) the dialog will show, the user can interact"
-               << "with it and the appropriate signals will be emitted on close. However, the"
                    << "exec() call never returns, stack content at the time of the exec() call"
                    << "is leaked, and the exec() call may interfere with input event processing";
         emscripten_sleep(1); // This call never returns
-#endif
+    }
     // For the asyncify case we do nothing here and wait for events in wait()
 }
 
@@ -393,7 +401,7 @@ bool QEventDispatcherWasm::wait(int timeout)
 #endif
     Q_ASSERT(emscripten_is_main_runtime_thread());
     Q_ASSERT(isMainThreadEventDispatcher());
-#ifdef QT_HAVE_EMSCRIPTEN_ASYNCIFY
+    if (qt_have_asyncify()) {
         if (timeout > 0)
             qWarning() << "QEventDispatcherWasm asyncify wait with timeout is not supported; timeout will be ignored"; // FIXME
 
@@ -403,10 +411,10 @@ bool QEventDispatcherWasm::wait(int timeout)
             return false;
         }
         return true;
-#else
+    } else {
         qWarning("QEventLoop::WaitForMoreEvents is not supported on the main thread without asyncify");
         Q_UNUSED(timeout);
-#endif
+    }
     return false;
 }
 
@@ -424,12 +432,10 @@ bool QEventDispatcherWasm::wakeEventDispatcherThread()
     }
 #endif
     Q_ASSERT(isMainThreadEventDispatcher());
-#ifdef QT_HAVE_EMSCRIPTEN_ASYNCIFY
     if (g_is_asyncify_suspended) {
         runOnMainThread([]{ qt_asyncify_resume(); });
         return true;
     }
-#endif
     return false;
 }
 

tests/manual/wasm/eventloop/asyncify_exec/CMakeLists.txt

@@ -7,3 +7,6 @@ qt_internal_add_manual_test(asyncify_exec
     LIBRARIES
         Qt::Core
 )
+
+# Enable asyncify for this test. Also enable optimizations in order to reduce the binary size.
+target_link_options(asyncify_exec PUBLIC -sASYNCIFY -Os)

tests/manual/wasm/eventloop/asyncify_exec/main.cpp

@@ -2,14 +2,12 @@
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 #include <QtCore>
 
-// This test shows how to asyncify enables blocking
-// the main thread on QEventLoop::exec(), while event
-// provessing continues.
+// This test shows how to use asyncify to enable blocking the main
+// thread on QEventLoop::exec(), while event processing continues.
 int main(int argc, char **argv)
 {
     QCoreApplication app(argc, argv);
 
-#ifdef QT_HAVE_EMSCRIPTEN_ASYNCIFY
     QTimer::singleShot(1000, []() {
 
         QEventLoop loop;
@@ -22,10 +20,6 @@ int main(int argc, char **argv)
         loop.exec();
         qDebug() << "Returned from QEventLoop::exec()";
     });
-#else
-        qDebug() << "This test requires Emscripten asyncify. To enable,"
-                 << "configure Qt with -device-option QT_EMSCRIPTEN_ASYNCIFY=1";
-#endif
 
     app.exec();
 }