use std::sync::Arc;use std::time::Instant; use gpui::{App, Global, ReadGlobal, SharedString};use parking_lot::RwLock; #[derive(Default)]struct FontFamilyCacheState {    loaded_at: Option<Instant>,    font_families: Vec<SharedString>,} /// A cache for the list of font families.////// Listing the available font families from the text system is expensive,/// so we do it once and then use the cached values each render.#[derive(Default)]pub struct FontFamilyCache {    state: RwLock<FontFamilyCacheState>,} #[derive(Default)]struct GlobalFontFamilyCache(Arc<FontFamilyCache>); impl Global for GlobalFontFamilyCache {} impl FontFamilyCache {    /// Initializes the global font family cache.    pub fn init_global(cx: &mut App) {        cx.default_global::<GlobalFontFamilyCache>();    }     /// Returns the global font family cache.    pub fn global(cx: &App) -> Arc<Self> {        GlobalFontFamilyCache::global(cx).0.clone()    }     /// Returns the list of font families.    pub fn list_font_families(&self, cx: &App) -> Vec<SharedString> {        if self.state.read().loaded_at.is_some() {            return self.state.read().font_families.clone();        }         let mut lock = self.state.write();        lock.font_families = cx            .text_system()            .all_font_names()            .into_iter()            .map(SharedString::from)            .collect();        lock.loaded_at = Some(Instant::now());         lock.font_families.clone()    }}