Python: Add support for invoke_from_event_loop

Fixes #420

api/python/lib.rs

@@ -20,6 +20,18 @@ fn quit_event_loop() -> Result<(), errors::PyEventLoopError> {
     slint_interpreter::quit_event_loop().map_err(|e| e.into())
 }
 
+#[pyfunction]
+fn invoke_from_event_loop(callable: PyObject) -> Result<(), errors::PyEventLoopError> {
+    slint_interpreter::invoke_from_event_loop(move || {
+        Python::with_gil(|py| {
+            if let Err(err) = callable.call0(py) {
+                eprintln!("Error invoking python callable from closure invoked via slint::invoke_from_event_loop: {}", err)
+            }
+        })
+    })
+    .map_err(|e| e.into())
+}
+
 use pyo3::prelude::*;
 
 #[pymodule]
@@ -42,6 +54,7 @@ fn slint(_py: Python<'_>, m: &PyModule) -> PyResult<()> {
     m.add_class::<models::PyModelBase>()?;
     m.add_function(wrap_pyfunction!(run_event_loop, m)?)?;
     m.add_function(wrap_pyfunction!(quit_event_loop, m)?)?;
+    m.add_function(wrap_pyfunction!(invoke_from_event_loop, m)?)?;
 
     Ok(())
 }

api/python/tests/test_invoke_from_event_loop.py

@@ -0,0 +1,29 @@
+# Copyright © SixtyFPS GmbH <[email protected]>
+# SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-1.1 OR LicenseRef-Slint-commercial
+
+from slint import slint as native
+import threading
+from datetime import timedelta
+
+
+def test_threads():
+    global was_here
+    was_here = False
+
+    def invoked_from_event_loop():
+        global was_here
+        was_here = True
+        native.quit_event_loop()
+
+    def quit():
+        native.invoke_from_event_loop(invoked_from_event_loop)
+
+    thr = threading.Thread(target=quit)
+    native.Timer.single_shot(timedelta(milliseconds=10), lambda: thr.start())
+    fallback_timer = native.Timer()
+    fallback_timer.start(native.TimerMode.Repeated, timedelta(
+        milliseconds=100), native.quit_event_loop)
+    native.run_event_loop()
+    thr.join()
+    fallback_timer.stop()
+    assert was_here == True