ENH: Make deferring connections the default for main window again for better performance

pydm/data_plugins/__init__.py

@@ -29,7 +29,19 @@
 
 
 @contextmanager
-def connection_queue(defer_connections=False):
+def connection_queue(defer_connections: bool = False) -> None:
+    """
+    Creates a queue for holding channel connections and potentially processing them at a later time. When
+    defer_connections is set to True, the exit from the context manager will not result in any connections being made.
+    This allows for a more responsive end user experience on displays with many connections as it will load without
+    needing to establish all connections first.
+    Parameters
+    ----------
+    defer_connections : bool
+        Whether or not to defer making the actual connections to channels at a later time. Note that if this
+        is set to true, a call to establish_queued_connections() must be made at some point later as the queue
+        will not be automatically be processed by the context manager in this case.
+    """
     global __CONNECTION_QUEUE__
     global __DEFER_CONNECTIONS__
     if __CONNECTION_QUEUE__ is None:
@@ -41,7 +53,11 @@ def connection_queue(defer_connections=False):
     establish_queued_connections()
 
 
-def establish_queued_connections():
+def establish_queued_connections() -> None:
+    """
+    Processes all channels in the deferred connection queue establishing the actual connection for each. Upon
+    completion, will reset the global connection queue to None.
+    """
     global __DEFER_CONNECTIONS__
     global __CONNECTION_QUEUE__
     if __CONNECTION_QUEUE__ is None:

pydm/display.py

@@ -9,13 +9,14 @@
 from io import StringIO
 from os import path
 from string import Template
-from typing import Dict, Optional, Tuple
+from typing import Dict, List, Optional, Tuple
 
 import re
 import six
 from qtpy import uic
 from qtpy.QtWidgets import QApplication, QWidget
 
+from . import data_plugins
 from .utilities import import_module_by_filename, is_pydm_app, macro
 
 
@@ -28,7 +29,11 @@ class ScreenTarget:
 logger = logging.getLogger(__file__)
 
 
-def load_file(file, macros=None, args=None, target=ScreenTarget.NEW_PROCESS):
+def load_file(file: str,
+              macros: Optional[Dict[str, str]] = None,
+              args: Optional[List[str]] = None,
+              target: ScreenTarget = ScreenTarget.NEW_PROCESS,
+              defer_connections: bool = False):
     """
     Load .ui, .py, or .adl screen file, perform macro substitution, then return
     the resulting QWidget.
@@ -47,6 +52,11 @@ def load_file(file, macros=None, args=None, target=ScreenTarget.NEW_PROCESS):
     target : int
         One of the ScreenTarget targets. PROCESS is only available when used
         with PyDM Application for now.
+    defer_connections : bool
+        If set to true, the loading of channel connections will be deferred until the
+        connection queue is flushed via a data_plugins.establish_queued_connections() call. This
+        results in the display being responsive to the user faster as it does not wait on
+        establishing connections during initial display creation.
 
     Returns
     -------
@@ -66,7 +76,8 @@ def load_file(file, macros=None, args=None, target=ScreenTarget.NEW_PROCESS):
     _, extension = os.path.splitext(file)
     loader = _extension_to_loader.get(extension, load_py_file)
     logger.debug("Loading %s file by way of %s...", file, loader.__name__)
-    w = loader(file, args=args, macros=macros)
+    with data_plugins.connection_queue(defer_connections=defer_connections):
+        w = loader(file, args=args, macros=macros)
     if target == ScreenTarget.DIALOG:
         w.show()
 

pydm/main_window.py

@@ -17,6 +17,7 @@
 from .widgets.rules import register_widget_rules, unregister_widget_rules
 from . import config
 import subprocess
+import threading
 import platform
 import logging
 
@@ -352,7 +353,8 @@ def open(self, filename, macros=None, args=None, target=None):
         new_widget = load_file(filename,
                                macros=macros,
                                args=args,
-                               target=target)
+                               target=target,
+                               defer_connections=True)
         if new_widget:
             if self.home_widget is None:
                 self.home_widget = new_widget
@@ -370,6 +372,10 @@ def open(self, filename, macros=None, args=None, target=None):
             self.ui.actionEdit_in_Designer.setText(edit_in_text)
             if (self.designer_path and ui_file) or (py_file and not ui_file):
                 self.ui.actionEdit_in_Designer.setEnabled(True)
+
+        # Create and run the thread for establishing the channel connections which have been queued above
+        establish_connections_thread = threading.Thread(target=data_plugins.establish_queued_connections, daemon=True)
+        establish_connections_thread.start()
         return new_widget
 
     def load_tool(self, checked):

pydm/tests/test_display.py

@@ -1,9 +1,7 @@
 import os
 import pytest
-from pydm import Display
-from pydm.display import load_py_file, _compile_ui_file
-from qtpy.QtWidgets import QWidget
-import pydm.utilities.stylesheet
+from pydm import Display, data_plugins
+from pydm.display import load_file, load_py_file, _compile_ui_file, ScreenTarget
 
 # The path to the .ui file used in these tests
 test_ui_path = os.path.join(
@@ -114,3 +112,16 @@ def test_compile_ui_file():
     assert class_name == 'Ui_Form'
     assert 'setupUi(self' in code_string
     assert 'retranslateUi(self' in code_string
+
+
+def test_defer_connections(qtbot):
+    """
+    Verify that when the defer_connections parameter is set to true, connections are held up in a queue
+    until it is time to process them
+    """
+    load_file(valid_display_test_py_path, target=ScreenTarget.HOME, defer_connections=True)
+
+    # The test file loaded has one connection to TST:Val1. Since defer_connections is True, verify
+    # that this address has been placed in the queue.
+    assert 'TST:Val1' == data_plugins.__CONNECTION_QUEUE__[0].address
+    data_plugins.__CONNECTION_QUEUE__ = None