Function start

packages/node/src/backend/nodeBackend.ts:623–699

()

  const backend: RuntimeBackend = {
    async start(): Promise<void> {
      if (disposed) throw new Error("NodeBackend: disposed");
      if (fatal !== null) throw fatal;
      if (started) return;
      assertWorkerEnvironmentSupported(opts.nativeShimModule);

      if (worker === null) {
        if (initConfigResolved === null) {
          const resolvedEmojiWidthPolicy = await resolveBackendEmojiWidthPolicy(
            cfg.emojiWidthPolicy,
            nativeConfig,
          );
          const nativeWidthPolicy = applyEmojiWidthPolicy(resolvedEmojiWidthPolicy);
          initConfigResolved = {
            ...initConfigBase,
            widthPolicy: nativeWidthPolicy,
          };
        } else {
          // Keep core measurement policy deterministic across stop/start cycles.
          const widthPolicy = initConfigResolved[WIDTH_POLICY_KEY];
          if (typeof widthPolicy === "number") {
            setTextMeasureEmojiPolicy(widthPolicy === 0 ? "narrow" : "wide");
          }
        }

        startDef = deferred<void>();
        startSettled = false;
        stopDef = null;
        stopSettled = false;
        stopRequested = false;
        if (sabFrameTransport !== null) resetSabFrameTransport(sabFrameTransport);

        const workerData =
          opts.nativeShimModule === undefined
            ? undefined
            : { nativeShimModule: opts.nativeShimModule };
        const workerEntry = resolveWorkerEntry(workerData);
        worker = new Worker(workerEntry.entry, workerEntry.options);
        if (frameAudit.enabled) {
          frameAudit.emit("worker.spawn", {
            frameTransport: frameTransportWire.kind,
            frameSabSlotCount: frameSabSlotCount,
            frameSabSlotBytes: frameSabSlotBytes,
            workerEntry: workerEntry.entry.href,
          });
        }
        exitDef = deferred<void>();
        worker.on("message", handleWorkerMessage);
        worker.on("error", (err) => {
          if (fatal !== null) return;
          fatal = new ZrUiError("ZRUI_BACKEND_ERROR", safeErr(err).message);
          failAll(fatal);
        });
        worker.on("exit", (code) => {
          handleWorkerExit(code);
        });

        send({ type: "init", config: initConfigResolved });