Convert window list to doubly-linked and fix restack prev pointer bug - #46
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jEsuSdA wants to merge 1 commit into
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Convert window list to doubly-linked and fix restack prev pointer bug#46jEsuSdA wants to merge 1 commit into
jEsuSdA wants to merge 1 commit into
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Currently the window list is singly-linked, so restack_win() and finish_destroy_win() must scan the entire list to find the previous element. This is O(n) for both operations. Add a prev pointer to the win struct and maintain it correctly: - add_win(): sets prev when inserting at the head or after another window - restack_win(): unhooks and rehooks using prev directly, no linear scan This also fixes a subtle bug in restack_win(): when inserting at the end of the list (new_above not found), the old code could leave the prev pointer inconsistent, causing finish_destroy_win() to corrupt the list head and paint_all() to traverse an empty list, resulting in a grey screen. finish_destroy_win() now uses the prev pointer to unlink in O(1) instead of scanning from the head each time.
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Summary
Converts the window list from singly-linked to doubly-linked, eliminating O(n) scans in
restack_win()andfinish_destroy_win(). Also fixes a subtle bug that could cause grey screen regions when restacking windows.Problem
The window list is currently singly-linked. Both
restack_win()andfinish_destroy_win()must scan the entire list to find the previous element:restack_win()scans twice (unhook + rehook)finish_destroy_win()scans once per destroyed windowAdditionally,
restack_win()has a subtle bug when inserting at the end of the list: the previous pointer of the former last node is not updated correctly, which can corrupt the list head pointer. Whenfinish_destroy_win()later frees a window at the end,paint_all()may traverse an empty list and paint nothing → grey screen.Solution
Add a
prevpointer to thewinstruct and maintain it correctly:add_win(): setsprevwhen inserting at the head or after another windowrestack_win(): unhooks and rehooks usingprevdirectly, no linear scan. Tracksnew_predduring the rehook loop to correctly setprevwhen inserting at the endfinish_destroy_win(): usesprevpointer to unlink in O(1) instead of scanning from the headChanges
cm-window.h— addsstruct _win *prevfieldfastcompmgr.c— updatesadd_win(),restack_win(),finish_destroy_win()Scope
make clean && makeproduces zero warnings, zero errorsImpact
restack_win()andfinish_destroy_win()are now O(1) instead of O(n)