feat: session load perf (#17186)

2 files changed, 148 insertions, 0 deletions

diff --git a/packages/app/src/context/global-sync/session-prefetch.test.ts b/packages/app/src/context/global-sync/session-prefetch.test.ts
new file mode 100644
index 000000000..f039b02ca
--- /dev/null
+++ b/packages/app/src/context/global-sync/session-prefetch.test.ts
@@ -0,0 +1,63 @@
+import { describe, expect, test } from "bun:test"
+import {
+  clearSessionPrefetch,
+  clearSessionPrefetchDirectory,
+  getSessionPrefetch,
+  runSessionPrefetch,
+  setSessionPrefetch,
+} from "./session-prefetch"
+
+describe("session prefetch", () => {
+  test("stores and clears message metadata by directory", () => {
+    clearSessionPrefetch("/tmp/a", ["ses_1"])
+    clearSessionPrefetch("/tmp/b", ["ses_1"])
+
+    setSessionPrefetch({
+      directory: "/tmp/a",
+      sessionID: "ses_1",
+      limit: 200,
+      complete: false,
+      at: 123,
+    })
+
+    expect(getSessionPrefetch("/tmp/a", "ses_1")).toEqual({ limit: 200, complete: false, at: 123 })
+    expect(getSessionPrefetch("/tmp/b", "ses_1")).toBeUndefined()
+
+    clearSessionPrefetch("/tmp/a", ["ses_1"])
+
+    expect(getSessionPrefetch("/tmp/a", "ses_1")).toBeUndefined()
+  })
+
+  test("dedupes inflight work", async () => {
+    clearSessionPrefetch("/tmp/c", ["ses_2"])
+
+    let calls = 0
+    const run = () =>
+      runSessionPrefetch({
+        directory: "/tmp/c",
+        sessionID: "ses_2",
+        task: async () => {
+          calls += 1
+          return { limit: 100, complete: true, at: 456 }
+        },
+      })
+
+    const [a, b] = await Promise.all([run(), run()])
+
+    expect(calls).toBe(1)
+    expect(a).toEqual({ limit: 100, complete: true, at: 456 })
+    expect(b).toEqual({ limit: 100, complete: true, at: 456 })
+  })
+
+  test("clears a whole directory", () => {
+    setSessionPrefetch({ directory: "/tmp/d", sessionID: "ses_1", limit: 10, complete: true, at: 1 })
+    setSessionPrefetch({ directory: "/tmp/d", sessionID: "ses_2", limit: 20, complete: false, at: 2 })
+    setSessionPrefetch({ directory: "/tmp/e", sessionID: "ses_1", limit: 30, complete: true, at: 3 })
+
+    clearSessionPrefetchDirectory("/tmp/d")
+
+    expect(getSessionPrefetch("/tmp/d", "ses_1")).toBeUndefined()
+    expect(getSessionPrefetch("/tmp/d", "ses_2")).toBeUndefined()
+    expect(getSessionPrefetch("/tmp/e", "ses_1")).toEqual({ limit: 30, complete: true, at: 3 })
+  })
+})
diff --git a/packages/app/src/context/global-sync/session-prefetch.ts b/packages/app/src/context/global-sync/session-prefetch.ts
new file mode 100644
index 000000000..10877b063
--- /dev/null
+++ b/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)
+  }
+}