enh: prevent GUI from locking when transferring large file

CHANGELOG

@@ -1,5 +1,6 @@
 0.6.0
  - feat: generalize GUI to use all recipes
+ - enh: prevent GUI from locking when transferring large file
  - enh: re-use tree count information for transfer progress bar
  - enh: display the actual directory tree instead of a table
  - enh: compute file hash while copying, avoiding reading data twice

mpl_data_cast/gui/main.py

@@ -3,7 +3,9 @@
 import signal
 import pathlib
 import sys
+import threading
 import traceback
+from typing import Dict
 
 import dclab
 import h5py
@@ -151,10 +153,20 @@ def on_task_transfer(self) -> None:
                                  self.widget_output.path)
 
         tree_counter = self.widget_input.tree_counter
-        with Callback(self, tree_counter) as path_callback:
+        with CastingCallback(self, tree_counter) as callback:
+            # run the casting operation in a separate thread
+            caster = CastingThread(rp, callback=callback)
+            caster.start()
 
-            result = rp.cast(path_callback=path_callback)
-            self.widget_output.trigger_recount_objects()
+        while not caster.result:
+            QtWidgets.QApplication.processEvents(
+                QtCore.QEventLoop.ProcessEventsFlag.AllEvents, 300)
+            time.sleep(.1)
+
+        caster.join()
+        result = caster.result
+
+        self.widget_output.trigger_recount_objects()
 
         if result["success"]:
             self.progressBar.setValue(100)
@@ -177,7 +189,7 @@ def on_task_transfer(self) -> None:
         self.pushButton_transfer.setEnabled(True)
 
 
-class Callback:
+class CastingCallback:
     """Makes it possible to execute code everytime a file was processed.
     Used for updating the progress bar and calculating the processing rate."""
 
@@ -208,11 +220,20 @@ def __call__(self, path) -> None:
             # go to undetermined state
             self.gui.progressBar.setRange(0, 0)
 
-        QtWidgets.QApplication.processEvents(
-            QtCore.QEventLoop.ProcessEventsFlag.AllEvents, 300)
         self.counter += 1
 
 
+class CastingThread(threading.Thread):
+    def __init__(self, rp, callback, *args, **kwargs):
+        super(CastingThread, self).__init__(*args, **kwargs)
+        self.rp = rp
+        self.callback = callback
+        self.result = {}
+
+    def run(self):
+        self.result = self.rp.cast(callback=self.callback)
+
+
 def excepthook(etype, value, trace) -> None:
     """
     Handler for all unhandled exceptions.