1 files changed, 157 insertions, 0 deletions
diff --git a/devtools/client/shared/worker-utils.js b/devtools/client/shared/worker-utils.js
new file mode 100644
index 0000000000..bb5c54dac3
--- /dev/null
+++ b/devtools/client/shared/worker-utils.js
@@ -0,0 +1,157 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+"use strict";
+
+class WorkerDispatcher {
+  #msgId = 1;
+  #worker = null;
+  // Map of message ids -> promise resolution functions, for dispatching worker responses
+  #pendingCalls = new Map();
+  #url = "";
+
+  constructor(url) {
+    this.#url = url;
+  }
+
+  start() {
+    // When running in debugger jest test, we don't have access to ChromeWorker
+    if (typeof ChromeWorker == "function") {
+      this.#worker = new ChromeWorker(this.#url);
+    } else {
+      this.#worker = new Worker(this.#url);
+    }
+    this.#worker.onerror = err => {
+      console.error(`Error in worker ${this.#url}`, err.message);
+    };
+    this.#worker.addEventListener("message", this.#onMessage);
+  }
+
+  stop() {
+    if (!this.#worker) {
+      return;
+    }
+
+    this.#worker.removeEventListener("message", this.#onMessage);
+    this.#worker.terminate();
+    this.#worker = null;
+    this.#pendingCalls.clear();
+  }
+
+  task(method, { queue = false } = {}) {
+    const calls = [];
+    const push = args => {
+      return new Promise((resolve, reject) => {
+        if (queue && calls.length === 0) {
+          Promise.resolve().then(flush);
+        }
+
+        calls.push({ args, resolve, reject });
+
+        if (!queue) {
+          flush();
+        }
+      });
+    };
+
+    const flush = () => {
+      const items = calls.slice();
+      calls.length = 0;
+
+      if (!this.#worker) {
+        this.start();
+      }
+
+      const id = this.#msgId++;
+      this.#worker.postMessage({
+        id,
+        method,
+        calls: items.map(item => item.args),
+      });
+
+      this.#pendingCalls.set(id, items);
+    };
+
+    return (...args) => push(args);
+  }
+
+  invoke(method, ...args) {
+    return this.task(method)(...args);
+  }
+
+  #onMessage = ({ data: result }) => {
+    const items = this.#pendingCalls.get(result.id);
+    this.#pendingCalls.delete(result.id);
+    if (!items) {
+      return;
+    }
+
+    if (!this.#worker) {
+      return;
+    }
+
+    result.results.forEach((resultData, i) => {
+      const { resolve, reject } = items[i];
+
+      if (resultData.error) {
+        const err = new Error(resultData.message);
+        err.metadata = resultData.metadata;
+        reject(err);
+      } else {
+        resolve(resultData.response);
+      }
+    });
+  };
+}
+
+function workerHandler(publicInterface) {
+  return function (msg) {
+    const { id, method, calls } = msg.data;
+
+    Promise.all(
+      calls.map(args => {
+        try {
+          const response = publicInterface[method].apply(undefined, args);
+          if (response instanceof Promise) {
+            return response.then(
+              val => ({ response: val }),
+              err => asErrorMessage(err)
+            );
+          }
+          return { response };
+        } catch (error) {
+          return asErrorMessage(error);
+        }
+      })
+    ).then(results => {
+      globalThis.postMessage({ id, results });
+    });
+  };
+}
+
+function asErrorMessage(error) {
+  if (typeof error === "object" && error && "message" in error) {
+    // Error can't be sent via postMessage, so be sure to convert to
+    // string.
+    return {
+      error: true,
+      message: error.message,
+      metadata: error.metadata,
+    };
+  }
+
+  return {
+    error: true,
+    message: error == null ? error : error.toString(),
+    metadata: undefined,
+  };
+}
+
+// Might be loaded within a worker thread where `module` isn't available.
+if (typeof module !== "undefined") {
+  module.exports = {
+    WorkerDispatcher,
+    workerHandler,
+  };
+}