How Unloading Hidden Tabs Works

This chapter explains how file tabs out of sight give their editors back to save memory. The user side is in Unload Hidden Tabs; the tabs themselves are in How the editor works.

Why we need it

EditorGroupContent.svelte keeps one FileView per file tab and only hides the inactive ones, so switching back is instant and keeps the cursor, scroll and unsaved edits. The price is a full CodeMirror editor, its DOM, blame and change marks for every tab: about 4 MB each, measured (Measuring Setting Memory). People keep many tabs open and look at a few. Memory is a feature here (see Architecture), so tabs nobody looks at should not hold it.

How it works

The app already had a sleeping state: tabs restored at start are dormant. repoStore.dormantTabs holds their keys (groupId plus path), Workspace.svelte renders no FileView for them, and showing one creates its editor at the saved position. Unloading reuses exactly that state.

sequenceDiagram
    participant App as App.svelte
    participant Store as repoStore
    participant Plan as tabSleep.ts
    participant View as FileView
    loop every 30 s while the setting is on
        App->>Store: sleepHiddenTabs(minutes * 60000)
        Store->>Plan: tabsToSleep(entries, tabShownAt, now, delay)
        Plan-->>Store: keys hidden long enough
        Store->>Store: add them to dormantTabs
    end
    Store-->>View: unmount: notePosition, view.destroy()
    Note over Store: the user clicks the tab
    Store->>Store: tabsChanged: wake it, copy tabPositions to pendingPositions
    Store-->>View: mount: load the file, takePendingPosition

Loading

• When a tab was last seen. repoStore.tabShownAt maps each tab key to the last time it was on screen. tabsChanged stamps the active tab of every group, and every sweep stamps them again, so a tab that has been active for an hour starts counting when it is hidden, not an hour ago.
• The decision. tabsToSleep in src/lib/stores/tabSleep.ts is pure: a shown tab, or one seen for the first time, gets now; a hidden tab that is eligible and older than the delay is returned. Closed tabs are forgotten. Eligible means a file tab (isFileTab) without unsaved edits that is not dormant already.
• Going to sleep. sleepHiddenTabs adds the keys to dormantTabs. Svelte unmounts the FileView, whose cleanup calls notePosition (caret and the last measured top line) and destroys the view.
• Waking up. Clicking the tab makes it active; tabsChanged drops the key and copies the tab's tabPositions entry into pendingPositions, which the new editor reads with takePendingPosition, the same path Reopen tabs on start uses.

The Markdown view mode survives because viewMode.ts remembers it per file for the session.

Where the code lives

File	What it does
src/lib/stores/tabSleep.ts	tabsToSleep, UNLOAD_TAB_MINUTES, TAB_SLEEP_CHECK_MS, pickUnloadTabMinutes
src/lib/stores/repo.svelte.ts	sleepHiddenTabs, tabShownAt, waking in tabsChanged
src/lib/App.svelte	The 30 second interval, only while the setting is on
src/lib/stores/settingsData.ts	unloadHiddenTabs (true) and unloadHiddenTabsMinutes (15)
src/lib/views/settings/EditorFeatureSettings.svelte	The switch and the Unload after choices

Design decisions

Reuse the dormant state. A second way to tear down and rebuild an editor would need its own position and wake logic. Dormant tabs already had both and were tested by every restart.

Never unsaved edits. Keeping unsaved text outside an editor would need a second copy and a new path back into the editor. Skipping dirty tabs keeps work safe with no new code.

Minutes, not a tab count. A tab limit already closes tabs by count. Time keeps the tabs you switch between often loaded, whatever their number.

A plain interval. The check is a few map lookups every 30 seconds with no IPC, so it also runs while the window is in the background, where freeing memory helps the most.

Undo history goes. CodeMirror's history lives in the editor state. Keeping it would mean keeping the state, which is most of the memory.

Tests

• src/lib/stores/tabSleep.test.ts: counting from the first hidden sighting, the shown tab never sleeps, tabs that cannot sleep, closed tabs forgotten, the minute choices.
• src/lib/stores/settingsData.test.ts: the defaults and their checks.

Keeping this page in sync

• Update this page and Unload Hidden Tabs when dormant tabs, FileView positions or the tab kinds change.
• If another tab kind learns to sleep, add it to eligible in sleepHiddenTabs and to both pages.
• Retake settings-unload-hidden-tabs.png when the rows change.