Improve home page loading speed using background update

validata_ui/ui_util.py

 """Util UI functions."""
+import threading
+
 from flask import flash
 
 
@@ -20,3 +22,34 @@ def flash_success(msg):
 def flash_info(msg):
     """Flash bootstrap info message."""
     flash(msg, "info")
+
+
+class ThreadUpdater:
+    """Fire last known value and update on background."""
+
+    def __init__(self, func):
+        # First time run to get an initial value
+        self.val = func()
+
+        self.func = func
+        self.thread = None
+
+    @property
+    def value(self):
+        self._background_update()
+        return self.val
+
+    def _background_update(self):
+        # Don't run if an update is already running
+        if self.thread is not None:
+            return
+
+        # Run func to update self.val and reset self.thread
+        # to show that background update is done.
+        def doIt():
+            self.val = self.func()
+            self.thread = None
+
+        # Init and start thread
+        self.thread = threading.Thread(target=doIt)
+        self.thread.start()

validata_ui/views.py

@@ -27,7 +27,7 @@ from validata_core.helpers import (
 
 from . import app, config, fetch_schema, pdf_service, schema_catalog_registry
 from .model import Section
-from .ui_util import flash_error, flash_warning
+from .ui_util import ThreadUpdater, flash_error, flash_warning
 from .validata_util import strip_accents
 
 log = logging.getLogger(__name__)
@@ -556,67 +556,70 @@ def retrieve_schema_catalog(section: Section):
 # Routes
 
 
-@app.route("/")
-def home():
-    """Home page."""
+def iter_sections():
+    """Yield sections of the home page, filled with schema metadata."""
+    # Iterate on all sections
+    for section in config.CONFIG.homepage.sections:
 
-    def iter_sections():
-        """Yield sections of the home page, filled with schema metadata."""
-        # Iterate on all sections
-        for section in config.CONFIG.homepage.sections:
+        # section with only links to external validators
+        if section.links:
+            yield section
+            continue
 
-            # section with only links to external validators
-            if section.links:
-                yield section
-                continue
+        # section with catalog
+        if section.catalog is None:
+            # skip section
+            continue
 
-            # section with catalog
-            if section.catalog is None:
-                # skip section
-                continue
+        # retrieving schema catatalog
+        schema_catalog, catalog_error = retrieve_schema_catalog(section)
+        if schema_catalog is None:
+            yield catalog_error
+            continue
 
-            # retrieving schema catatalog
-            schema_catalog, catalog_error = retrieve_schema_catalog(section)
-            if schema_catalog is None:
-                yield catalog_error
+        # Working on catalog
+        schema_info_list = []
+        for schema_reference in schema_catalog.references:
+            # retain tableschema only
+            if schema_reference.get_schema_type() != "tableschema":
                 continue
 
-            # Working on catalog
-            schema_info_list = []
-            for schema_reference in schema_catalog.references:
-                # retain tableschema only
-                if schema_reference.get_schema_type() != "tableschema":
-                    continue
-                # Loads default table schema for each schema reference
-                schema_info = {"name": schema_reference.name}
-                try:
-                    table_schema = fetch_schema(schema_reference.get_schema_url())
-                except json.JSONDecodeError:
-                    schema_info["err"] = True
-                    schema_info["title"] = (
-                        f"le format du schéma « {schema_info['name']} » "
-                        "n'est pas reconnu"
-                    )
-                except Exception:
-                    schema_info["err"] = True
-                    schema_info["title"] = (
-                        f"le schéma « {schema_info['name']} » " "n'est pas disponible"
-                    )
-                else:
-                    schema_info["title"] = (
-                        table_schema.get("title") or schema_info["name"]
-                    )
-                schema_info_list.append(schema_info)
-            schema_info_list = sorted(
-                schema_info_list, key=lambda sc: strip_accents(sc["title"].lower())
-            )
+            # Loads default table schema for each schema reference
+            schema_info = {"name": schema_reference.name}
+            try:
+                table_schema = fetch_schema(schema_reference.get_schema_url())
+            except json.JSONDecodeError:
+                schema_info["err"] = True
+                schema_info["title"] = (
+                    f"le format du schéma « {schema_info['name']} » "
+                    "n'est pas reconnu"
+                )
+            except Exception:
+                schema_info["err"] = True
+                schema_info["title"] = (
+                    f"le schéma « {schema_info['name']} » " "n'est pas disponible"
+                )
+            else:
+                schema_info["title"] = table_schema.get("title") or schema_info["name"]
+            schema_info_list.append(schema_info)
+        schema_info_list = sorted(
+            schema_info_list, key=lambda sc: strip_accents(sc["title"].lower())
+        )
 
-            yield {
-                **{k: v for k, v in section.dict().items() if k != "catalog"},
-                "catalog": schema_info_list,
-            }
+        yield {
+            **{k: v for k, v in section.dict().items() if k != "catalog"},
+            "catalog": schema_info_list,
+        }
+
+
+section_updater = ThreadUpdater(lambda: list(iter_sections()))
+
+
+@app.route("/")
+def home():
+    """Home page."""
 
-    return render_template("home.html", config=config, sections=list(iter_sections()))
+    return render_template("home.html", config=config, sections=section_updater.value)
 
 
 @app.route("/pdf")