Add initial Qt-trio integration

Use the new "guest mode" available on trio master branch.  Add
entrypoint for `pyqtgraph` based charting based on the `Quantdom`
project.

piker/ui/qt/_exec.py

@@ -0,0 +1,117 @@
+"""
+Trio - Qt integration
+
+Run ``trio`` in guest mode on top of the Qt event loop.
+All global Qt runtime settings are mostly defined here.
+"""
+import traceback
+from datetime import datetime
+
+import PyQt5  # noqa
+from pyqtgraph import QtGui
+from PyQt5 import QtCore
+from PyQt5.QtCore import pyqtRemoveInputHook
+import qdarkstyle
+import trio
+from outcome import Error
+
+from _chart import QuotesTabWidget
+from quantdom.base import Symbol
+from quantdom.loaders import get_quotes
+
+
+# Taken from Quantdom
+class MainWindow(QtGui.QMainWindow):
+
+    size = (800, 500)
+    title = 'piker: chart'
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        # self.setMinimumSize(*self.size)
+        self.setWindowTitle(self.title)
+
+
+def run_qtrio(
+    func,
+    args,
+    main_widget,
+) -> None:
+
+    # avoids annoying message when entering debugger from qt loop
+    pyqtRemoveInputHook()
+
+    app = QtGui.QApplication.instance()
+    if app is None:
+        app = PyQt5.QtWidgets.QApplication([])
+
+    # This code is from Nathaniel:
+
+    # This is substantially faster than using a signal... for some
+    # reason Qt signal dispatch is really slow (and relies on events
+    # underneath anyway, so this is strictly less work)
+    REENTER_EVENT = QtCore.QEvent.Type(QtCore.QEvent.registerEventType())
+
+    class ReenterEvent(QtCore.QEvent):
+        pass
+
+    class Reenter(QtCore.QObject):
+        def event(self, event):
+            event.fn()
+            return False
+
+    reenter = Reenter()
+
+    def run_sync_soon_threadsafe(fn):
+        event = ReenterEvent(REENTER_EVENT)
+        event.fn = fn
+        app.postEvent(reenter, event)
+
+    def done_callback(outcome):
+        print(f"Outcome: {outcome}")
+        if isinstance(outcome, Error):
+            exc = outcome.error
+            traceback.print_exception(type(exc), exc, exc.__traceback__)
+        app.quit()
+
+    # load dark theme
+    app.setStyleSheet(qdarkstyle.load_stylesheet(qt_api='pyqt5'))
+
+    # make window and exec
+    window = MainWindow()
+    instance = main_widget()
+
+    widgets = {
+        'window': window,
+        'main': instance,
+    }
+
+    # guest mode
+    trio.lowlevel.start_guest_run(
+        func,
+        widgets,
+        run_sync_soon_threadsafe=run_sync_soon_threadsafe,
+        done_callback=done_callback,
+    )
+
+    window.main_widget = main_widget
+    window.setCentralWidget(instance)
+    window.show()
+    app.exec_()
+
+
+async def plot_aapl(widgets):
+    qtw = widgets['main']
+    s = Symbol(ticker='AAPL', mode=Symbol.SHARES)
+    get_quotes(
+        symbol=s.ticker,
+        date_from=datetime(1900, 1, 1),
+        date_to=datetime(2030, 12, 31),
+    )
+    # spawn chart
+    qtw.update_chart(s)
+    await trio.sleep_forever()
+
+
+if __name__ == '__main__':
+    run_qtrio(plot_aapl, (), QuotesTabWidget)