core: writer-owned relocation

The worker no longer copies rows when an array cannot grow in place. It
reserves a zeroed region, returns the staged descriptor with a commit
flag, and queues every other request until the main thread (the only
writer) has copied the old bytes and sent commit-rows. Writes that raced
the old worker-side copy were lost; lights in the glTF viewer regularly
ended up at the origin because of it.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b2dd-db32-712d-99ce-12ce4a86d979
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

core/worker.js

@@ -2,10 +2,13 @@ import initWasm, { Core } from "./pkg/yawn_core.js";
 
 let core;
 let profileTimer;
+// While a relocation is staged, every request except its commit waits here.
+let awaitingCommit = false;
+const queue = [];
 
 const fail = code => { throw new Error(code); };
 
-addEventListener("message", async ({ data: message }) => {
+async function handle(message) {
   try {
     let result;
     if (message?.type === "init") {
@@ -21,15 +24,22 @@ addEventListener("message", async ({ data: message }) => {
       switch (message?.type) {
         case "create-rows":
           result = JSON.parse(core.create_rows(message.name, message.rows, message.stride, message.format));
+          awaitingCommit = result.commit;
           break;
         case "create-rows-batch":
           result = JSON.parse(core.create_rows_batch(JSON.stringify(message.rows)));
+          awaitingCommit = result.commit.length > 0;
+          break;
+        case "commit-rows":
+          awaitingCommit = false;
+          core.commit_rows(JSON.stringify(message.names));
           break;
         case "delete-rows":
           core.delete_rows(message.name);
           break;
         case "allocate-object":
           result = JSON.parse(core.allocate_object(message.name, message.count ?? 1));
+          awaitingCommit = result.commit;
           break;
         case "delete-object":
           core.delete_object(message.name, message.id);
@@ -74,4 +84,13 @@ addEventListener("message", async ({ data: message }) => {
   } catch (error) {
     postMessage({ request: message?.request, error: error?.message ?? "CORE_ERROR" });
   }
+}
+
+addEventListener("message", async ({ data: message }) => {
+  if (awaitingCommit && message?.type !== "commit-rows") {
+    queue.push(message);
+    return;
+  }
+  await handle(message);
+  while (!awaitingCommit && queue.length) await handle(queue.shift());
 });