Llama2c WASM UI improvements (#732)

* pass seed, expose model seq_len

* wip new llama2.c ui

* final new UI example

* small coppy

* copy

candle-wasm-examples/llama2-c/llama2cWorker.js

@@ -0,0 +1,96 @@
+import init, { Model } from "./build/m.js";
+
+async function fetchArrayBuffer(url) {
+  const res = await fetch(url, {
+    cache: "force-cache",
+  });
+  const data = await res.arrayBuffer();
+  return new Uint8Array(data);
+}
+
+class Llama2C {
+  static instance = {};
+
+  static async getInstance(weightsURL, modelID, tokenizerURL) {
+    // load individual modelID only once
+    if (!this.instance[modelID]) {
+      await init();
+
+      self.postMessage({ status: "loading", message: "Loading Model" });
+
+      const [weightsArrayU8, tokenizerArrayU8] = await Promise.all([
+        fetchArrayBuffer(weightsURL),
+        fetchArrayBuffer(tokenizerURL),
+      ]);
+
+      this.instance[modelID] = new Model(weightsArrayU8, tokenizerArrayU8);
+    }
+    return this.instance[modelID];
+  }
+}
+
+let controller = null;
+self.addEventListener("message", (event) => {
+  if (event.data.command === "start") {
+    controller = new AbortController();
+    generate(event.data);
+  } else if (event.data.command === "abort") {
+    controller.abort();
+  }
+});
+
+async function generate(data) {
+  const {
+    weightsURL,
+    modelID,
+    tokenizerURL,
+    prompt,
+    temp,
+    repeatPenalty,
+    seed,
+    maxSeqLen,
+  } = data;
+  try {
+    self.postMessage({ status: "loading", message: "Starting llama2.c" });
+    const model = await Llama2C.getInstance(weightsURL, modelID, tokenizerURL);
+
+    self.postMessage({ status: "loading", message: "Initializing model" });
+    model.init_with_prompt(prompt, temp, repeatPenalty, seed);
+
+    const seq_len = model.get_seq_len();
+
+    let sentence = "";
+    let max_tokens = maxSeqLen ? maxSeqLen : seq_len - prompt.length - 1;
+
+    while (max_tokens--) {
+      await new Promise(async (resolve) => {
+        if (controller && controller.signal.aborted) {
+          self.postMessage({
+            status: "aborted",
+            message: "Aborted",
+            output: prompt + sentence,
+          });
+          return;
+        }
+        const token = await model.next_token();
+
+        sentence += token;
+        self.postMessage({
+          status: "generating",
+          message: "Generating token",
+          token: token,
+          sentence: sentence,
+          prompt: prompt,
+        });
+        setTimeout(resolve, 0);
+      });
+    }
+    self.postMessage({
+      status: "complete",
+      message: "complete",
+      output: prompt + sentence,
+    });
+  } catch (e) {
+    self.postMessage({ error: e });
+  }
+}