[Backport] Add initial support for coroutines

- when a signal calls a Python function and it is a coroutine, it will be scheduled
(patch by Florian Link)

(cherry picked from commit MeVisLab/pythonqt@f6e8ea7)

Author: mrbean-bremen

src/PythonQt.cpp

@@ -88,6 +88,16 @@ void PythonQt::init(int flags, const QByteArray& pythonQtModuleName)
       _self->_p->_pySourcelessFileLoader = importlib.getVariable("SourcelessFileLoader");
     }
 
+#ifdef PY3K
+    PythonQtObjectPtr asyncio;
+    asyncio.setNewRef(PyImport_ImportModule("asyncio"));
+    if (asyncio)
+    {
+      _self->_p->_pyEnsureFuture = asyncio.getVariable("ensure_future");
+      _self->_p->_pyFutureClass = asyncio.getVariable("Future");
+    }
+#endif
+
     PythonQt::priv()->setupSharedLibrarySuffixes();
 
     PythonQtMethodInfo::addParameterTypeAlias("QObjectList", "QList<QObject*>");
@@ -406,6 +416,46 @@ void PythonQtPrivate::setTaskDoneCallback(const PythonQtObjectPtr & callable)
   _pyTaskDoneCallback = callable;
 }
 
+PythonQtObjectPtr PythonQtPrivate::checkAndRunCoroutine(const PythonQtObjectPtr& object)
+{
+  PythonQtObjectPtr result;
+#ifdef PY3K
+  if (!PyCoro_CheckExact(object))
+  {
+    return result;
+  }
+
+  if (!_pyEnsureFuture)
+  {
+    std::cerr << "PythonQt: ensure_future not initialized" << std::endl;
+    return PythonQtObjectPtr();
+  }
+  PyObject* args = PyTuple_New(1);
+  PyObject* coro = object.object();
+  Py_INCREF(coro);
+  PyTuple_SetItem(args, 0, coro);
+  PyObject* r = PyObject_CallObject(_pyEnsureFuture, args);
+  result.setNewRef(r);
+  if (_pyTaskDoneCallback) {
+    PyObject* methodName = PyUnicode_FromString("add_done_callback");
+    PyObject_CallMethodObjArgs(r, methodName, _pyTaskDoneCallback.object(), nullptr);
+    Py_XDECREF(methodName);
+  }
+  Py_XDECREF(args);
+#endif
+  return result;
+}
+
+PythonQtObjectPtr PythonQtPrivate::createAsyncioFuture()
+{
+  if (!_pyFutureClass)
+  {
+    std::cerr << "PythonQt: _pyFutureClass not initialized" << std::endl;
+    return nullptr;
+  }
+  return _pyFutureClass.call();
+}
+
 void PythonQt::setRedirectStdInCallback(PythonQtInputChangedCB* callback, void * callbackData)
 {
   if (!callback) {

src/PythonQt.h

@@ -686,6 +686,12 @@ class PYTHONQT_EXPORT PythonQtPrivate : public QObject {
   //! created by checkAndRunCoroutine
   void setTaskDoneCallback(const PythonQtObjectPtr& callable);
 
+  //! Runs the given coroutine (via asyncio), returns a scheduled task if it object is a coroutine.
+  PythonQtObjectPtr checkAndRunCoroutine(const PythonQtObjectPtr& object);
+
+  //! Creates a new asyncio.Future object
+  PythonQtObjectPtr createAsyncioFuture();
+
   //! get the suffixes that are used for shared libraries
   const QStringList& sharedLibrarySuffixes() { return _sharedLibrarySuffixes; }
 
@@ -865,6 +871,8 @@ class PYTHONQT_EXPORT PythonQtPrivate : public QObject {
 
   PythonQtObjectPtr _pySourceFileLoader;
   PythonQtObjectPtr _pySourcelessFileLoader;
+  PythonQtObjectPtr _pyEnsureFuture;
+  PythonQtObjectPtr _pyFutureClass;
 
   PythonQtObjectPtr _pyTaskDoneCallback;
 

src/PythonQtSignalReceiver.cpp

@@ -55,6 +55,7 @@ void PythonQtSignalTarget::call(void **arguments) const {
   PYTHONQT_GIL_SCOPE
   PyObject* result = call(_callable, methodInfo(), arguments);
   if (result) {
+    PythonQt::priv()->checkAndRunCoroutine(result);
     Py_DECREF(result);
   }
 }