From 811ee649cd691d0ff1752f146c022a079a92f874 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <prudiger@anaconda.com>
Date: Wed, 21 Sep 2022 15:47:50 +0200
Subject: [PATCH] Throttle events in pyodide

---
 panel/_templates/pyodide_worker.js |  5 ++--
 panel/io/convert.py                | 39 ++++++++++++++++++++++++------
 panel/io/pyodide.py                | 21 ++++++++++------
 3 files changed, 49 insertions(+), 16 deletions(-)

diff --git a/panel/_templates/pyodide_worker.js b/panel/_templates/pyodide_worker.js
index ff966b9b1a..b455b4b48f 100644
--- a/panel/_templates/pyodide_worker.js
+++ b/panel/_templates/pyodide_worker.js
@@ -37,14 +37,15 @@ self.onmessage = async (event) => {
     from panel.io.state import state
     from panel.io.pyodide import _link_docs_worker
 
-    _link_docs_worker(state.curdoc, sendPatch)
+    _link_docs_worker(state.curdoc, sendPatch, setter='js')
     `)
   } else if (event.data.type === 'patch') {
     self.pyodide.runPythonAsync(`
     import json
 
-    state.curdoc.apply_json_patch(json.loads('${event.data.patch}'))
+    state.curdoc.apply_json_patch(json.loads('${event.data.patch}'), setter='js')
     `)
+    self.postMessage({type: 'idle'})
   }
 }
 
diff --git a/panel/io/convert.py b/panel/io/convert.py
index 2e05ee28fc..edfa1b45e2 100644
--- a/panel/io/convert.py
+++ b/panel/io/convert.py
@@ -108,19 +108,44 @@ def _stdlibs():
 PYODIDE_WORKER_SCRIPT = """
 <script type="text/javascript">
 const pyodideWorker = new Worker("./{{ name }}.js");
+pyodideWorker.busy = false
+pyodideWorker.queue = []
 
 function send_change(jsdoc, event) {
-  if (event.setter_id != null)
+  if (event.setter_id != null && event.setter_id == 'py') {
     return
+  } else if (pyodideWorker.busy && event.model && event.attr) {
+    let events = []
+    for (const old_event of pyodideWorker.queue) {
+      if (!(old_event.model === event.model && old_event.attr === event.attr)) {
+        events.push(old_event)
+      }
+    }
+    events.push(event)
+    pyodideWorker.queue = events
+    return
+  }
   const patch = jsdoc.create_json_patch_string([event])
+  pyodideWorker.busy = true
   pyodideWorker.postMessage({type: 'patch', patch: patch})
 }
 
 pyodideWorker.onmessage = async (event) => {
-  if (event.data.type === 'render') {
-    const docs_json = JSON.parse(event.data.docs_json)
-    const render_items = JSON.parse(event.data.render_items)
-    const root_ids = JSON.parse(event.data.root_ids)
+  const msg = event.data
+
+  if (msg.type === 'idle') {
+    if (pyodideWorker.queue.length) {
+      const patch = pyodideWorker.jsdoc.create_json_patch_string(pyodideWorker.queue)
+      pyodideWorker.busy = true
+      pyodideWorker.queue = []
+      pyodideWorker.postMessage({type: 'patch', patch: patch})
+    } else {
+      pyodideWorker.busy = false
+    }
+  } else if (msg.type === 'render') {
+    const docs_json = JSON.parse(msg.docs_json)
+    const render_items = JSON.parse(msg.render_items)
+    const root_ids = JSON.parse(msg.root_ids)
 
     // Remap roots in message to element IDs
     const root_els = document.getElementsByClassName('bk-root')
@@ -148,8 +173,8 @@ def _stdlibs():
     pyodideWorker.jsdoc = jsdoc = views[0].model.document
     jsdoc.on_change(send_change.bind(null, jsdoc), false)
     pyodideWorker.postMessage({'type': 'rendered'})
-  } else if (event.data.type === 'patch') {
-    pyodideWorker.jsdoc.apply_json_patch(JSON.parse(event.data.patch), event.data.buffers, setter_id='js')
+  } else if (msg.type === 'patch') {
+    pyodideWorker.jsdoc.apply_json_patch(JSON.parse(msg.patch), msg.buffers, setter_id='py')
   }
 };
 </script>
diff --git a/panel/io/pyodide.py b/panel/io/pyodide.py
index 6f3e2bc929..63636902cb 100644
--- a/panel/io/pyodide.py
+++ b/panel/io/pyodide.py
@@ -129,7 +129,7 @@ def _model_json(model: Model, target: str) -> Tuple[Document, str]:
         version   = __version__,
     ))
 
-def _link_docs(pydoc: Document, jsdoc: Any) -> None:
+def _link_docs(pydoc: Document, jsdoc: Any, setter: str | None =None) -> None:
     """
     Links Python and JS documents in Pyodide ensuring taht messages
     are passed between them.
@@ -140,29 +140,32 @@ def _link_docs(pydoc: Document, jsdoc: Any) -> None:
         The Python Bokeh Document instance to sync.
     jsdoc: Javascript Document
         The Javascript Bokeh Document instance to sync.
+    setter: str
+        Setter ID used for suppressing events.
     """
     def jssync(event):
-        if (getattr(event, 'setter_id', None) is not None):
+        if (event.setter_id is not None and event.setter_id == setter):
             return
-        events = [event]
-        json_patch = jsdoc.create_json_patch_string(pyodide.ffi.to_js(events))
-        pydoc.apply_json_patch(json.loads(json_patch))
+        json_patch = jsdoc.create_json_patch_string(pyodide.ffi.to_js([event]))
+        pydoc.apply_json_patch(json.loads(json_patch), setter=setter)
 
     jsdoc.on_change(pyodide.ffi.create_proxy(jssync), pyodide.ffi.to_js(False))
 
     def pysync(event):
+        if event.setter is not None and event.setter == setter:
+            return
         json_patch, buffers = process_document_events([event], use_buffers=True)
         buffer_map = {}
         for (ref, buffer) in buffers:
             buffer_map[ref['id']] = pyodide.ffi.to_js(buffer).buffer
-        jsdoc.apply_json_patch(JSON.parse(json_patch), pyodide.ffi.to_js(buffer_map), setter_id='js')
+        jsdoc.apply_json_patch(JSON.parse(json_patch), pyodide.ffi.to_js(buffer_map), setter_id=setter)
 
     pydoc.on_change(pysync)
     pydoc.callbacks.trigger_json_event(
         {'event_name': 'document_ready', 'event_values': {}
     })
 
-def _link_docs_worker(doc: Document, dispatch_fn: Any, msg_id: str | None = None):
+def _link_docs_worker(doc: Document, dispatch_fn: Any, msg_id: str | None = None, setter: str | None = None):
     """
     Links the Python document to a dispatch_fn which can be used to
     sync messages between a WebWorker and the main thread in the
@@ -174,10 +177,14 @@ def _link_docs_worker(doc: Document, dispatch_fn: Any, msg_id: str | None = None
         The document to dispatch messages from.
     dispatch_fn: JS function
         The Javascript function to dispatch messages to.
+    setter: str
+        Setter ID used for suppressing events.
     msg_id: str | None
         An optional message ID to pass through to the dispatch_fn.
     """
     def pysync(event):
+        if setter is not None and event.setter == setter:
+            return
         json_patch, buffers = process_document_events([event], use_buffers=True)
         buffer_map = {}
         for (ref, buffer) in buffers: