openbox/menuframe: optimize menu list construction and counting #36
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This patch introduces two optimizations for large menus: 1. Caches the number of menu entries in `num_entries`. This eliminates O(N) calls to `g_list_length` during geometry updates and placement calculations (e.g., `menu_frame_move_on_screen`). 2. Optimizes menu population loop from O(N^2) to O(N). Replaces `g_list_append` (which scans the list) inside the loop with `g_list_prepend` followed by a single `g_list_reverse` at the end. Together, these changes significantly reduce CPU usage when opening or navigating large menus (e.g., "All Applications" lists).
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This patch introduces two optimizations for large menus.
1. Cache the number of menu entries
The new
num_entriesfield stores the total number of menu items.This removes repeated O(N) calls to
g_list_lengthduring geometry updates and placement calculations such asmenu_frame_move_on_screen.2. Reduce menu population from O(N²) to O(N)
The previous implementation used
g_list_appendinside the population loop, causing a linear scan on every iteration.The replacement uses
g_list_prependin the loop and a singleg_list_reverseonce the loop is complete.Overall Effect
Together, these changes dramatically reduce CPU usage when opening or navigating very large menus (such as full “All Applications” views).
Performance Impact
For a menu with N items: