Remove the msg_throttle attribute (hardcode the throttle at 1).

docs/source/changelog.md

@@ -36,6 +36,7 @@ Major user-visible changes in ipywidgets 7.0 include:
 - The `IntText`, `BoundedIntText`, `FloatText`, and `BoundedFloatText` widgets are now rendered as HTML number inputs, and have a `step` attribute that controls the resolution. ([#1545](https://github.com/jupyter-widgets/ipywidgets/pull/1545))
 - The `Text.on_submit` callback is deprecated; instead, set `continuous_update` to `False` and observe the `value` attribute: `mywidget.observe(callback, 'value')`. The `Textarea.scroll_to_bottom` method was removed. ([#1545](https://github.com/jupyter-widgets/ipywidgets/pull/1545))
 - The `readout_format` attribute of number sliders now validates its argument. ([#1550](https://github.com/jupyter-widgets/ipywidgets/pull/1550))
+- The `msg_throttle` attribute on widgets is now gone, and the code has a hardcoded message throttle equivalent to `msg_throttle=1`. ([#1557](https://github.com/jupyter-widgets/ipywidgets/pull/1557))
 
 
 Major changes developers should be aware of include:

ipywidgets/widgets/widget.py

@@ -348,8 +348,6 @@ def get_view_spec(self):
         help="EXPERIMENTAL: The number of views of the model displayed in the frontend. This attribute is experimental and may change or be removed in the future. None signifies that views will not be tracked. Set this to 0 to start tracking view creation/deletion.").tag(sync=True)
     comm = Instance('ipykernel.comm.Comm', allow_none=True)
 
-    msg_throttle = Int(1, help="""Maximum number of sync msgs the front-end can send before receiving an idle msg from the back-end.""").tag(sync=True)
-
     keys = List(help="The traits which are synced.")
 
     @default('keys')

packages/base/src/widget.ts

@@ -63,7 +63,6 @@ class WidgetModel extends Backbone.Model {
             _view_name: null,
             _view_module_version: JUPYTER_WIDGETS_VERSION,
             _view_count: null,
-            msg_throttle: 1,
         };
     }
 
@@ -254,7 +253,7 @@ class WidgetModel extends Backbone.Model {
                 this._pending_msgs--;
                 // Send buffer if one is waiting and we are below the throttle.
                 if (this._msg_buffer !== null
-                    && this._pending_msgs < (this.get('msg_throttle') || 1) ) {
+                    && this._pending_msgs < 1 ) {
                     this.send_sync_message(this._msg_buffer, this._msg_buffer_callbacks);
                     this._msg_buffer = null;
                     this._msg_buffer_callbacks = null;
@@ -359,7 +358,7 @@ class WidgetModel extends Backbone.Model {
             let callbacks = options.callbacks || this.callbacks();
 
             // Check throttle.
-            if (this._pending_msgs >= (this.get('msg_throttle') || 1)) {
+            if (this._pending_msgs >= 1) {
                 // The throttle has been exceeded, buffer the current msg so
                 // it can be sent once the kernel has finished processing
                 // some of the existing messages.

packages/base/test/src/manager_test.ts

@@ -434,7 +434,6 @@ describe("ManagerBase", function() {
                 "_view_name":"TestWidgetView",
                 "_view_module_version":"1.0.0",
                 "_view_count":null,
-                "msg_throttle":1
         }}}};
         expect(state).to.deep.equal(expectedState);
       });

packages/base/test/src/widget_test.ts

@@ -559,7 +559,6 @@ describe("WidgetModel", function() {
                 _view_name: null,
                 _view_module_version: '3.0.0',
                 _view_count: null,
-                msg_throttle: 1,
                 a: 'get_state test'
             });
         });
@@ -614,38 +613,6 @@ describe("WidgetModel", function() {
                 b: 'change b again'
             });
         });
-        it('works with message throttle 2', function() {
-            let send = sinon.spy(this.widget, 'send_sync_message');
-            this.widget.set('msg_throttle', 2);
-            this.widget.set('a', 'sync test');
-            this.widget.save_changes();
-            this.widget.set('a', 'another sync test');
-            this.widget.set('b', 'change b');
-            this.widget.save_changes();
-            this.widget.set('b', 'change b again');
-            this.widget.save_changes();
-
-            // check that one sync message went through
-            expect(send).to.be.calledTwice;
-            expect(send.firstCall).to.be.calledWith({
-                a: 'sync test',
-                msg_throttle: 2
-            })
-            expect(send.secondCall).to.be.calledWith({
-                a: 'another sync test',
-                b: 'change b'
-            })
-            // have the comm send a status idle message
-            this.widget._handle_status({
-                content: {
-                    execution_state: 'idle'
-                }
-            });
-            // check that the other sync message went through with the updated values
-            expect(send.thirdCall).to.be.calledWith({
-                b: 'change b again'
-            });
-        });
 
         it('Initial values are *not* sent on creation', function() {
             expect(this.comm.send.callCount).to.equal(0);

packages/schema/messages.md

@@ -241,9 +241,8 @@ The core idea of widgets is that some state is automatically synced back and for
 * `_view_module`: the view module
 * `_view_module_version`: the semver range of the view
 * `_view_name`: the name of the view
-* `msg_throttle`: an integer - the number of messages allowed 'in flight' for throttling purposes
 
-The `_model_*` and `_view_*` fields are assumed immutable (set at initialization, and never changed). The `msg_throttle` field can be changed.
+The `_model_*` and `_view_*` fields are assumed immutable (set at initialization, and never changed).
 
 ## Implementating the Jupyter widgets protocol in the kernel