init_headers in daemon thread, and fix #1996

gui/qt/__init__.py

@@ -43,9 +43,9 @@ from electrum.paymentrequest import InvoiceStore
 from electrum.contacts import Contacts
 from electrum.synchronizer import Synchronizer
 from electrum.verifier import SPV
-from electrum.util import DebugMem
+from electrum.util import DebugMem, UserCancelled
 from electrum.wallet import Abstract_Wallet
-from installwizard import InstallWizard
+from installwizard import InstallWizard, GoBack
 
 
 try:
@@ -191,6 +191,10 @@ class ElectrumGui:
     def main(self):
         try:
             self.init_network()
+        except UserCancelled:
+            return
+        except GoBack:
+            return
         except:
             traceback.print_exc(file=sys.stdout)
             return

gui/qt/installwizard.py

@@ -396,6 +396,7 @@ class InstallWizard(QDialog, MessageBoxMixin, BaseWizard):
         choices = [_("Auto connect"), _("Select server manually")]
         title = _("How do you want to connect to a server? ")
         clayout = ChoicesLayout(message, choices)
+        self.back_button.setText(_('Cancel'))
         self.set_main_layout(clayout.layout(), title)
         r = clayout.selected_index()
         if r == 0:

lib/blockchain.py

@@ -112,7 +112,8 @@ class Blockchain(util.PrintError):
             import urllib, socket
             socket.setdefaulttimeout(30)
             self.print_error("downloading ", self.headers_url)
-            urllib.urlretrieve(self.headers_url, filename)
+            urllib.urlretrieve(self.headers_url, filename + '.tmp')
+            os.rename(filename + '.tmp', filename)
             self.print_error("done.")
         except Exception:
             self.print_error("download failed. creating file", filename)

lib/network.py

@@ -813,7 +813,12 @@ class Network(util.DaemonThread):
             self.process_responses(interface)
 
     def run(self):
-        self.blockchain.init()
+        import threading
+        t = threading.Thread(target = self.blockchain.init)
+        t.daemon = True
+        t.start()
+        while t.isAlive() and self.is_running():
+            t.join(1)
         while self.is_running():
             self.maintain_sockets()
             self.wait_on_sockets()