From 16cbb7cb91a5b59e9c9907b64b2e02d7027ea5c0 Mon Sep 17 00:00:00 2001
From: Tom Pollard <tom.pollard@codethink.co.uk>
Date: Wed, 4 Dec 2019 13:49:47 +0000
Subject: userconfig.yaml: Add bool for disabling console output throttling

Also highlight the change & configuration in NEWS
---
 NEWS                                 | 10 ++++++++++
 src/buildstream/_context.py          | 15 ++++++++++++++-
 src/buildstream/_frontend/app.py     |  8 ++++++--
 src/buildstream/data/userconfig.yaml |  3 +++
 4 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/NEWS b/NEWS
index 602b14b51..293085cfe 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,16 @@ API
     Plugins authors that do this and believe BuildStream should be testing that
     part of their plugins should open an issue on BuildStream.
 
+Miscellaneous
+-------------
+
+  o By default the update rate of builstream console output
+    (e.g. messages & status updates) when executing a scheduler driven task is
+    restricted to once per second, known as the tick, with messages being batched
+    in the intervening periods if necessary. This restriction can be lifted with
+    `throttle-ui-updates: False` in user configuration. Logging behaviour remains
+    unaffected by this configuration.
+
 
 ==================
 buildstream 1.91.3
diff --git a/src/buildstream/_context.py b/src/buildstream/_context.py
index 9642edd49..513754a4c 100644
--- a/src/buildstream/_context.py
+++ b/src/buildstream/_context.py
@@ -114,6 +114,9 @@ class Context:
         # Format string for printing message lines in the master log
         self.log_message_format = None
 
+        # Wether to rate limit the updating of the bst output where applicable
+        self.log_throttle_updates = None
+
         # Maximum number of fetch or refresh tasks
         self.sched_fetchers = None
 
@@ -337,7 +340,16 @@ class Context:
         # Load logging config
         logging = defaults.get_mapping("logging")
         logging.validate_keys(
-            ["key-length", "verbose", "error-lines", "message-lines", "debug", "element-format", "message-format"]
+            [
+                "key-length",
+                "verbose",
+                "error-lines",
+                "message-lines",
+                "debug",
+                "element-format",
+                "message-format",
+                "throttle-ui-updates",
+            ]
         )
         self.log_key_length = logging.get_int("key-length")
         self.log_debug = logging.get_bool("debug")
@@ -346,6 +358,7 @@ class Context:
         self.log_message_lines = logging.get_int("message-lines")
         self.log_element_format = logging.get_str("element-format")
         self.log_message_format = logging.get_str("message-format")
+        self.log_throttle_updates = logging.get_bool("throttle-ui-updates")
 
         # Load scheduler config
         scheduler = defaults.get_mapping("scheduler")
diff --git a/src/buildstream/_frontend/app.py b/src/buildstream/_frontend/app.py
index b7aeb040b..cd05b7f8d 100644
--- a/src/buildstream/_frontend/app.py
+++ b/src/buildstream/_frontend/app.py
@@ -91,6 +91,7 @@ class App:
 
         # Cached messages
         self._message_text = ""
+        self._cache_messages = None
 
         #
         # Early initialization
@@ -239,6 +240,9 @@ class App:
             # Propagate pipeline feedback to the user
             self.context.messenger.set_message_handler(self._message_handler)
 
+            # Check if throttling frontend updates to tick rate
+            self._cache_messages = self.context.log_throttle_updates
+
             # Allow the Messenger to write status messages
             self.context.messenger.set_render_status_cb(self._render)
 
@@ -803,8 +807,8 @@ class App:
         text = self.logger.render(message)
         self._message_text += text
 
-        # If scheduler tick isn't active then render
-        if not self.stream.running:
+        # If we're not rate limiting messaging, or the scheduler tick isn't active then render
+        if not self._cache_messages or not self.stream.running:
             self._render(message_text=self._message_text)
 
         # Additionally log to a file
diff --git a/src/buildstream/data/userconfig.yaml b/src/buildstream/data/userconfig.yaml
index dc31c10ce..5b568167b 100644
--- a/src/buildstream/data/userconfig.yaml
+++ b/src/buildstream/data/userconfig.yaml
@@ -133,3 +133,6 @@ logging:
   message-format: |
 
     [%{elapsed}][%{key}][%{element}] %{action} %{message}
+
+  # Limit bst console output update rate to 1Hz where applicable
+  throttle-ui-updates: True
-- 
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