Web sockets for save&restore #3389

georgweiss · 2025-05-07T11:58:02Z

This PR adds a web sockets-based mechanism for save&restore whereby data changes on the service side are pushed as web socket messages to all connected clients.

On the Phoebus app side, the core-websocket module adds a web socket client using the native Java APIs. Clients of the WebSocketClient only need to specify a URI and a callback for receiving text messages. Optionally API clients may register callbacks to handle/debug connection and disconnection events. WebSocketClient should be generic enough to support multiple use cases, e.g. logbook or alarm logger UI.
WebSocketClient will by default try to reconnect to the remote service in case the remote peer is shut down.

The save&restore app makes use of the WebSocketClient to update the UI based on whatever the service pushes as web socket messages. This way all clients should be able to reflect changes done by all users.

…ization

core/websocket/src/main/java/org/phoebus/core/websocket/WebSocketClient.java

abrahamwolk

I have two questions:

Suppose the connection is lost between the client and the server, and suppose that changes were made to a snapshot before the connection was re-established. Will the client be notified of the changes that were made while the connection was lost?
How is the situation dealt with when a snapshot is simultaneously being worked on by two clients in possibly non-compatible ways? For instance, one client may remove a folder, while another client may simultaneously add a node to the folder, or rename the folder in question.

abrahamwolk · 2025-05-09T06:47:08Z

...e/app/src/main/java/org/phoebus/applications/saveandrestore/ui/SaveAndRestoreController.java

        List<String> selectedNodeIds =
                ((List<Node>) selectedNodes).stream().map(Node::getUniqueId).collect(Collectors.toList());
-        JobManager.schedule("copy nodes", monitor -> {
+        JobManager.schedule("Copy odes", monitor -> {


Should the first argument to JobManager.schedule() be "Copy nodes"?

abrahamwolk · 2025-05-09T07:20:07Z

...pp/src/main/java/org/phoebus/applications/saveandrestore/ui/snapshot/SnapshotController.java

     * @param snapshotNode An existing {@link Node} of type {@link NodeType#SNAPSHOT}
     */
-    public void loadSnapshot(Node snapshotNode) {
+    public synchronized void loadSnapshot(Node snapshotNode) {


This method is synchronized, but the call to loadSnapshotInternal() will most likely return before the job scheduled by JobManager.schedule() has run, which in turn most likely will return before the function submitted to Platform.runLater() has run. Is this correct?

You're right, need not be synchronized. Leftover from testing.

abrahamwolk · 2025-05-09T07:21:47Z

...store/app/src/main/java/org/phoebus/applications/saveandrestore/ui/snapshot/SnapshotTab.java

-                tabGraphicImageProperty.set(ImageRepository.SNAPSHOT);
-            }
-        }
+        //WebSocketClientService.getInstance().addWebSocketMessageHandler(this);


Commented-out code.

abrahamwolk · 2025-05-09T07:35:47Z

...n/java/org/phoebus/applications/saveandrestore/ui/configuration/ConfigurationController.java

-
-    private void loadConfigurationData(Runnable completion) {
-        UI_EXECUTOR.execute(() -> {
+    public synchronized void loadConfiguration(final Node node) {


This method is synchronized, but the functions submitted to JobManager.schedule() and Platform.runLater() are run asynchronously and will most likely return after this method has returned. Is this correct?

You're right, need not be synchronized. Leftover from testing.

georgweiss · 2025-05-09T10:06:44Z

I have two questions.

You have a point, will add update of UI when web socket is re-established. That said, in most cases the web socket would go away as a consequence of the service being shutdown or restarted. When service is offline no users can save changes.
This is intentionally not considered in any particular manner. Currently simultaneous edits are not handled in any particular manner, but with updates triggered by the web socket messages users would at least know that an object has been updated (and by whom!). In my view disallowing simultaneous edits would be a non-trivial, though interesting, challenge.

shroffk · 2025-05-09T14:23:52Z

regarding 2.
SAR will most likely not be a high throughput system where many people are editing and modifying the tree or nodes simultaneously... I fell like the complexity of adding that level of locking for consistent editing would be solving a problem that does not exist.
I think it would be better to inform users that the SAR does not have edit sessions and the last edit is what you see.

shroffk · 2025-05-09T14:24:38Z

When service is offline no users can save changes.

+1
refreshing UI on reconnect makes sense

abrahamwolk · 2025-05-12T06:20:55Z

Incompatible updates can still happen even though updates to snapshots are relatively infrequent. E.g., a computer may be left unattended with unsaved changes for some amount of time, or a client with unsaved changes may be disconnected for some amount of time because a computer was suspended.

One idea, that does not use locks, could be that each revision of a snapshot is given its own unique ID (perhaps implemented using a counter), and on writing, the unique ID of the revision that is overridden is compared on the server against the unique ID of the revision that the edit is based on. If they don't match, then the snapshot has been updated while editing took place, and an error or warning can be displayed.

georgweiss · 2025-05-12T07:01:52Z

Save & restore has been in use for quite some time without anything preventing simultaneous edits. Further, currently there is no way to refresh data other than collapsing/expanding nodes in the tree view. On top of that, an object being edited must be closed and reopened to reflect changes.

What web sockets add is a way to make sure the UI reflects changes made by others. Safeguarding against simultaneous edits is in my view not in scope for this PR and the introduction of web sockets.

abrahamwolk · 2025-05-12T07:21:56Z

What will user A see if user A is editing a snapshot, and user B writes to the snapshot?

georgweiss · 2025-05-12T07:38:35Z

Then user A will see the state saved by B and A's edits are lost. B's identity will be apparent from the updated UI.

abrahamwolk · 2025-05-12T12:49:26Z

...e/app/src/main/java/org/phoebus/applications/saveandrestore/ui/SaveAndRestoreController.java

    @Override
    public boolean handleTabClosed() {
-        saveLocalState();
+        //saveLocalState();


Commented-out line of code.

abrahamwolk · 2025-05-12T12:50:27Z

...e/app/src/main/java/org/phoebus/applications/saveandrestore/ui/SaveAndRestoreController.java

+
+    private void handleWebSocketConnected() {
+        serviceConnected.setValue(true);
+        Platform.runLater(() -> {


Why call Platform.runLater() with a function that does nothing? Both here and in handleWebSocketDisconnected().

georgweiss · 2025-05-12T12:53:23Z

Interesting observation (at least on MacOS): disabling WiFi does not trigger a web socket disconnect event. Moreover, when WiFi is enabled again, the web socket remains operational.

In any case, I have added a refresh of the UI when service is brought back on-line and client succeeds to reconnect.

georgweiss · 2025-05-13T11:35:44Z

Based on observations in various test scenarios: in order to handle different kind of web socket connection issues, a ping/pong strategy is needed. Therefore the client will dispatch a ping message and consider the connection dead if a pong message is not received within three seconds.

georgweiss added 30 commits March 8, 2025 17:43

Adding initial code for save&restore web socket API

549be41

Added missing web socket code, initial end-to-end test

f964711

Merge branch 'master' into CSSTUDIO-1967

25a2e4a

Ping/pong thread in web socket client

2905ea7

Ping/pong thread in web socket client

29e98e9

Some rework to handle data changes from save&restore

d1f1c0c

Resolve merge conflict

316f8cf

Put web socket client in core module

06e22fa

Minor refactoring

e2560d8

Remove web socket reconnect logic

6b2eafc

Send web socket message when tagging/untagging

fbcef08

Let SaveAndRestoreController request web socket connection on initial…

80233d7

…ization

Web socket messages for filters (add/update/remove)

892196b

Update unit tests

749c278

Fix unit test configuration

a2be6e2

Handle configuration update web socket messages, update unit tests

ed7b628

Unregister listener when save&restore configuration UI is closed

206d724

Fix configuration changes in UI

09f2fa2

Fix issues in configuration update through web socket message

e8a7256

Resolve merge conflicts

ddb6afe

Fix update configuration issue

3bc9209

Fix 'dirty' behavior

5519ab8

Snapshot view dirty visualization: same as configuration view

cb7a5a9

Move snapshot view icon handling to controller

4a7c1bb

Web socket handling in snapshot view controller

b6c4947

Fix build failure

5c63f78

Fix bug in snapshot update

0f70202

Improved UI update when nodes are added/removed

1a11d4e

Simplified deletion of node server side

58db4e5

Further simplifications to node deletion

7f1637e

georgweiss added 7 commits May 4, 2025 15:58

Display web socket message when nodes are moved

6bcade6

Finalize web socket messages related to filters

aa21840

Moved web socket client related code out of SaveAndRestoreService

bc0a73d

Refacotring to improve maintainability

6219fba

Web socket messages when nodes are copied

ea1d316

Code cleanup, javadoc and doc

7a9d940

Remove printout

3616a97

georgweiss requested review from abrahamwolk, kasemir and shroffk May 7, 2025 11:58

kasemir reviewed May 7, 2025

View reviewed changes

core/websocket/src/main/java/org/phoebus/core/websocket/WebSocketClient.java Outdated Show resolved Hide resolved

kasemir approved these changes May 7, 2025

View reviewed changes

Update logging of connection failure

0ce1b00

abrahamwolk reviewed May 9, 2025

View reviewed changes

Updates due to review feed-back

90b5dfa

Refresh UI when web socket client reconnects

7ea9f17

abrahamwolk reviewed May 12, 2025

View reviewed changes

Code cleanup

939154f

abrahamwolk approved these changes May 13, 2025

View reviewed changes

Ping/pong mechanism to handle connection issues in web socket

503dd4c

shroffk merged commit 286eee1 into master May 13, 2025
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Web sockets for save&restore #3389

Web sockets for save&restore #3389

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