Add TaskThread, use to simplify WaitingDialog

This will be useful as a client thread for hardware wallets

gui/qt/main_window.py

@@ -197,6 +197,10 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
         self.show()
         self.raise_()
 
+    def on_error(self, exc_info):
+        traceback.print_exception(*exc_info)
+        self.show_error(str(exc_info[1]))
+
     def on_network(self, event, *args):
         if event == 'updated':
             self.need_update.set()
@@ -1265,12 +1269,15 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
         # call hook to see if plugin needs gui interaction
         run_hook('sign_tx', parent, tx)
 
-        def sign_thread():
-            self.wallet.sign_transaction(tx, password)
-            return True
+        def on_signed(result):
+            callback(True)
+        def on_failed(exc_info):
+            self.on_error(exc_info)
+            callback(False)
 
-        WaitingDialog(parent, _('Signing transaction...'), sign_thread,
-                      callback)
+        task = partial(self.wallet.sign_transaction, tx, password)
+        WaitingDialog(parent, _('Signing transaction...'), task,
+                      on_signed, on_failed)
 
     def broadcast_transaction(self, tx, tx_desc, parent):
 
@@ -1309,7 +1316,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
                     self.show_error(msg, parent=parent)
 
         WaitingDialog(parent, _('Broadcasting transaction...'),
-                      broadcast_thread, broadcast_done)
+                      broadcast_thread, broadcast_done, self.on_error)
 
     def prepare_for_payment_request(self):
         self.tabs.setCurrentIndex(1)

gui/qt/util.py

@@ -4,6 +4,8 @@ import traceback
 import sys
 import threading
 import platform
+import Queue
+from collections import namedtuple
 from functools import partial
 
 from electrum.i18n import _
@@ -211,39 +213,26 @@ class WindowModalDialog(QDialog, MessageBoxMixin):
         if title:
             self.setWindowTitle(title)
 
-class WaitingDialog(QThread, MessageBoxMixin):
+
+class WaitingDialog(WindowModalDialog):
     '''Shows a please wait dialog whilst runnning a task.  It is not
     necessary to maintain a reference to this dialog.'''
-    def __init__(self, parent, message, task, on_finished=None):
-        global dialogs
-        dialogs.append(self) # Prevent GC
-        QThread.__init__(self)
-        self.task = task
-        self.on_finished = on_finished
-        self.dialog = WindowModalDialog(parent, _("Please wait"))
-        vbox = QVBoxLayout(self.dialog)
+    def __init__(self, parent, message, task, on_success=None, on_error=None):
+        assert parent
+        WindowModalDialog.__init__(self, parent, _("Please wait"))
+        vbox = QVBoxLayout(self)
         vbox.addWidget(QLabel(message))
-        self.dialog.show()
-        self.dialog.connect(self, SIGNAL("finished()"), self.finished)
-        self.start()
+        self.accepted.connect(self.on_accepted)
+        self.show()
+        self.thread = TaskThread(self)
+        self.thread.add(task, on_success, self.accept, on_error)
 
-    def run(self):
-        try:
-            self.result = self.task()
-            self.error = None
-        except BaseException as e:
-            traceback.print_exc(file=sys.stdout)
-            self.error = str(e)
-            self.result = None
+    def wait(self):
+        self.thread.wait()
+
+    def on_accepted(self):
+        self.thread.stop()
 
-    def finished(self):
-        global dialogs
-        dialogs.remove(self)
-        self.dialog.accept()
-        if self.error:
-            self.show_error(self.error, parent=self.dialog.parent())
-        if self.on_finished:
-            self.on_finished(self.result)
 
 def line_dialog(parent, title, label, ok_label, default=None):
     dialog = WindowModalDialog(parent, title)
@@ -548,6 +537,46 @@ class ButtonsTextEdit(QPlainTextEdit, ButtonsWidget):
         return o
 
 
+class TaskThread(QThread):
+    '''Thread that runs background tasks.  Callbacks are guaranteed
+    to happen in the context of its parent.'''
+
+    Task = namedtuple("Task", "task cb_success cb_done cb_error")
+    doneSig = pyqtSignal(object, object, object)
+
+    def __init__(self, parent, on_error=None):
+        super(TaskThread, self).__init__(parent)
+        self.on_error = on_error
+        self.tasks = Queue.Queue()
+        self.doneSig.connect(self.on_done)
+        self.start()
+
+    def add(self, task, on_success=None, on_done=None, on_error=None):
+        on_error = on_error or self.on_error
+        self.tasks.put(TaskThread.Task(task, on_success, on_done, on_error))
+
+    def run(self):
+        while True:
+            task = self.tasks.get()
+            if not task:
+                break
+            try:
+                result = task.task()
+                self.doneSig.emit(result, task.cb_done, task.cb_success)
+            except BaseException:
+                self.doneSig.emit(sys.exc_info(), task.cb_done, task.cb_error)
+
+    def on_done(self, result, cb_done, cb):
+        # This runs in the parent's thread.
+        if cb_done:
+            cb_done()
+        if cb:
+            cb(result)
+
+    def stop(self):
+        self.tasks.put(None)
+
+
 if __name__ == "__main__":
     app = QApplication([])
     t = WaitingDialog(None, 'testing ...', lambda: [time.sleep(1)], lambda x: QMessageBox.information(None, 'done', "done", _('OK')))