Improve performance of using active process data when rendering the tab bar by only scanning processes once per second

We dont bother with configurable ttl. Instead treat the start of caching
as the instant when cache freshness is checked. And ensure that cache is
re-used for every OS Window.

Fixes #9862
Fixes #9872

Author: kovidgoyal

docs/changelog.rst

@@ -243,6 +243,8 @@ Detailed list of changes
 
 - Render block elements from the Unicode Symbols for Legacy Computing Supplement block (U+1CC00–U+1CEBF): separated block quadrants, separated block sextants, one sixteenth blocks, and one quarter block partial fills (:disc:`9849`)
 
+- Improve performance of using active process data when rendering the tab bar by only scanning processes once per second (:iss:`9862`)
+
 0.46.2 [2026-03-21]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

kitty/boss.py

@@ -27,7 +27,7 @@
 
 from kitty.types import WindowResizeDrag
 
-from .child import cached_process_data, default_env, set_default_env
+from .child import cached_process_data, default_env, process_data_cache, set_default_env
 from .cli import create_opts, green, parse_args
 from .cli_stub import CLIOptions, SaveAsSessionOptions
 from .clipboard import (
@@ -1923,6 +1923,13 @@ def on_activity_since_last_focus(self, window: Window) -> None:
         if tm is not None:
             tm.mark_tab_bar_dirty()
 
+    def cache_process_data(self, enable: bool) -> None:
+        ' Turn on caching of process data. Must be called in enable/disable pairs. '
+        if enable:
+            self.process_data_cache_active = process_data_cache.start_caching()
+        else:
+            process_data_cache.stop_caching(self.process_data_cache_active)
+
     def update_tab_bar_data(self, os_window_id: int) -> None:
         tm = self.os_window_map.get(os_window_id)
         if tm is not None:

kitty/child-monitor.c

@@ -1001,6 +1001,7 @@ render(monotonic_t now, bool input_read) {
 
     const bool scan_for_animated_images = global_state.check_for_active_animated_images;
     global_state.check_for_active_animated_images = false;
+    call_boss(cache_process_data, "O", Py_True);
 
     for (size_t i = 0; i < global_state.num_os_windows; i++) {
         OSWindow *w = global_state.os_windows + i;
@@ -1021,6 +1022,7 @@ render(monotonic_t now, bool input_read) {
 
     }
     last_render_at = now;
+    call_boss(cache_process_data, "O", Py_False);
 #undef TD
 }
 

kitty/child.py

@@ -8,6 +8,7 @@
 from collections.abc import Generator, Sequence
 from contextlib import contextmanager, suppress
 from itertools import count
+from time import monotonic
 from typing import TYPE_CHECKING, DefaultDict, Iterable, Mapping, Optional, TypedDict
 
 import kitty.fast_data_types as fast_data_types
@@ -96,27 +97,48 @@ def checked_terminfo_dir() -> str | None:
     return terminfo_dir if os.path.isdir(terminfo_dir) else None
 
 
-def processes_in_group(grp: int) -> list[int]:
-    gmap: DefaultDict[int, list[int]] | None = getattr(process_group_map, 'cached_map', None)
-    if gmap is None:
-        try:
-            gmap = process_group_map()
-        except Exception:
-            gmap = defaultdict(list)
-    return gmap.get(grp, [])
+class CachedProcessData:
+
+    cached_result: DefaultDict[int, list[int]] | None = None
+    cache_active: bool = False
+    cache_at: float = 0
+    ttl: float = 1
+
+    def process_group_map(self) -> DefaultDict[int, list[int]]:
+        if self.cached_result is None or not self.cache_active:
+            try:
+                self.cached_result = process_group_map()
+            except Exception:
+                self.cached_result = defaultdict(list)
+            self.cache_at = monotonic()
+        return self.cached_result
+
+    def processes_in_group(self, grp: int) -> list[int]:
+        return self.process_group_map()[grp]
+
+    def start_caching(self, refresh: bool = False) -> bool:
+        prev, self.cache_active = self.cache_active, True
+        if refresh or monotonic() - self.cache_at > self.ttl:
+            self.cached_result = None
+            self.cache_at = 0
+        return prev
+
+    def stop_caching(self, prev: bool) -> None:
+        self.cache_active = prev
+        self.cached_result = None
+
+
+process_data_cache = CachedProcessData()
+processes_in_group = process_data_cache.processes_in_group
 
 
 @contextmanager
 def cached_process_data() -> Generator[None, None, None]:
-    try:
-        cm = process_group_map()
-    except Exception:
-        cm = defaultdict(list)
-    setattr(process_group_map, 'cached_map', cm)
+    orig = process_data_cache.start_caching(refresh=True)
     try:
         yield
     finally:
-        delattr(process_group_map, 'cached_map')
+        process_data_cache.stop_caching(orig)
 
 
 def session_id(pids: Iterable[int]) -> int: