feat: session load perf (#17186)

packages/app/src/context/global-sync/session-prefetch.ts

@@ -0,0 +1,85 @@
+const key = (directory: string, sessionID: string) => `${directory}\n${sessionID}`
+
+export const SESSION_PREFETCH_TTL = 15_000
+
+type Meta = {
+  limit: number
+  complete: boolean
+  at: number
+}
+
+const cache = new Map<string, Meta>()
+const inflight = new Map<string, Promise<Meta | undefined>>()
+const rev = new Map<string, number>()
+
+const version = (id: string) => rev.get(id) ?? 0
+
+export function getSessionPrefetch(directory: string, sessionID: string) {
+  return cache.get(key(directory, sessionID))
+}
+
+export function getSessionPrefetchPromise(directory: string, sessionID: string) {
+  return inflight.get(key(directory, sessionID))
+}
+
+export function clearSessionPrefetchInflight() {
+  inflight.clear()
+}
+
+export function isSessionPrefetchCurrent(directory: string, sessionID: string, value: number) {
+  return version(key(directory, sessionID)) === value
+}
+
+export function runSessionPrefetch(input: {
+  directory: string
+  sessionID: string
+  task: (value: number) => Promise<Meta | undefined>
+}) {
+  const id = key(input.directory, input.sessionID)
+  const pending = inflight.get(id)
+  if (pending) return pending
+
+  const value = version(id)
+
+  const promise = input.task(value).finally(() => {
+    if (inflight.get(id) === promise) inflight.delete(id)
+  })
+
+  inflight.set(id, promise)
+  return promise
+}
+
+export function setSessionPrefetch(input: {
+  directory: string
+  sessionID: string
+  limit: number
+  complete: boolean
+  at?: number
+}) {
+  cache.set(key(input.directory, input.sessionID), {
+    limit: input.limit,
+    complete: input.complete,
+    at: input.at ?? Date.now(),
+  })
+}
+
+export function clearSessionPrefetch(directory: string, sessionIDs: Iterable<string>) {
+  for (const sessionID of sessionIDs) {
+    if (!sessionID) continue
+    const id = key(directory, sessionID)
+    rev.set(id, version(id) + 1)
+    cache.delete(id)
+    inflight.delete(id)
+  }
+}
+
+export function clearSessionPrefetchDirectory(directory: string) {
+  const prefix = `${directory}\n`
+  const keys = new Set([...cache.keys(), ...inflight.keys()])
+  for (const id of keys) {
+    if (!id.startsWith(prefix)) continue
+    rev.set(id, version(id) + 1)
+    cache.delete(id)
+    inflight.delete(id)
+  }
+}