Added missing cache

discojs/discojs-web/src/dataset/data_loader/cache.ts

@@ -0,0 +1,60 @@
+export class Deferred<T> {
+    promise: Promise<T> = new Promise<T>(() => {})
+    resolve: (value: T | PromiseLike<T>) => void = () => {}
+    reject: (reason?: any) => void = () => {}
+
+    constructor() {
+        this.reset()
+    }
+
+    reset() {
+        this.promise = new Promise<T>((resolve, reject) => {
+            this.resolve = resolve
+            this.reject = reject
+        })
+    }
+}
+
+export class Cache<E> {
+    position: number = 0
+    private readonly cache: Deferred<E>[]
+
+    private constructor(
+        readonly length: number,
+        private readonly request: (
+            pos: number,
+            init?: boolean
+        ) => void | Promise<void>
+    ) {
+        this.cache = Array.from({ length }, () => new Deferred<E>())
+    }
+
+    // pre-loads the cache with the first n requests
+    static async init<E>(
+        length: number,
+        request: (pos: number, init?: boolean) => void | Promise<void>,
+        initializer: (c: Cache<E>) => void
+    ): Promise<Cache<E>> {
+        const cache = new Cache<E>(length, request)
+        initializer(cache)
+        for (let pos = 0; pos < length; pos++) {
+            cache.request(pos, true)
+        }
+        return cache
+    }
+
+    put(pos: number, elt: E): void {
+        const promise = this.cache[pos] as Deferred<E>
+        promise.resolve(elt)
+    }
+
+    async next(): Promise<E> {
+        const eltOrDeffered = this.cache[this.position]
+        const elt = await eltOrDeffered.promise
+        const pos = this.position
+        this.cache[pos] = new Deferred<E>()
+        this.request(pos)
+        this.position = (pos + 1) % this.length
+        return elt
+    }
+}