minor improvements; fix: error handler

README.md

@@ -1,13 +1,15 @@
 # Offload
 
-Offload cpu-itensive tasks using WebWorkers. Offload creates a limited execution pool and can operate in two modes:
+Offload heavy tasks using WebWorkers.
+
+Offload creates a limited execution pool and can operate in two modes:
 - callback mode (default) - spawns web workers on demand when the function is called, self terminated
 - background - runs workers as backround jobs, distributes load among them, must be terminated manually
 
 
-*Currently uses unstable api's.*
+*Currently uses unstable WebWorkers API.*
 
-To install:
+## Install:
 
 ```bash
 bun add githib:nesterow/offload # or pnpm
@@ -18,7 +20,7 @@ bun add githib:nesterow/offload # or pnpm
 Considering following worker:
 
 ```typescript
-// echo.worker.ts
+// print.worker.ts
 import { handler } from "@nesterow/offload";
 declare var self: Worker;
 
@@ -29,29 +31,51 @@ handler(async (data: string) => {
 });
 ```
 
+### Callback operation mode
+
 In the callback mode, `print()` will spawn a worker and terminate it after the task is done.
 Maximum of 5 workers may be spawned at the same time, the rest will be queued:
 
 ```typescript
 import { offload } from "@nesterow/offload";
 
-const [print, terminate] = offload<boolean, string>("./echo.worker.ts", 5);
+const [print, terminate] = offload<boolean, string>("./print.worker.ts", 5);
 
 await print("Hello, World!"); // => true
 ```
 
+Callback operatinal mode us useful when thread startup delay doesn't matter.
+You don't need to worry about worker termination as it exits after the callback returns result.
+This is default "safe" option as it allows to call `offload` in any part of the application.
+
+### Background operation mode
+
 In the background mode, offload will spawn 5 workers, `print()` will distribute the tasks among them:
 
 ```typescript
 import { offload } from "@nesterow/offload";
 
-const [print, terminate] = offload<boolean, string>("./echo.worker.ts", 5, 'bg');
+const [print, terminate] = offload<boolean, string>("./print.worker.ts", 5, 'bg');
 
 await print("Hello, World!"); // => true
 
 terminate(); // terminate all workers, for example on exit signal
 ```
 
+Background operation mode is useful when you need to spawn pre-defined number of the threads on application start.
+Generally it is more effective as it balances the load among the threads and doesn't have startup delay.
+
+## Types
+
+Because offload doesn't know params and return types of your worker, you need to pass type arguments manually:
+
+```typescript
+const [callback, termiate] = offload<ReturnType, ParamType>("./my.worker.ts", 1);
+
+const param: ParamType = {};
+const result: ReturnType = await callback(param: ParamType);
+```
+
 ## License
 
 MIT

index.js

@@ -38,11 +38,12 @@ function offload(url, poolSize = 1, mode = "cb") {
 function createTaskCallback(worker, eof) {
   const cb = async function(data) {
     const id = createTaskId();
-    worker.addEventListener("error", (event) => {
+    const errorCallback = (event) => {
       const error = event.message;
       workerTasks.get(worker)?.get(id)?.reject(new OffloadError(error, id));
       workerTasks.get(worker)?.delete(id);
-    }, { once: true });
+    };
+    worker.addEventListener("error", errorCallback, { once: true });
     const workerTask = Promise.withResolvers();
     workerTasks.get(worker)?.set(id, workerTask);
     const request = { id, params: data };
@@ -52,11 +53,13 @@ function createTaskCallback(worker, eof) {
       workerTasks.get(worker)?.delete(id);
       if (eof)
         eof();
+      worker.removeEventListener("error", errorCallback);
       return result;
     } catch (error) {
       workerTasks.get(worker)?.delete(id);
       if (eof)
         eof();
+      worker.removeEventListener("error", errorCallback);
       throw error;
     }
   };
@@ -132,11 +135,11 @@ function createTaskId() {
 function withMessageInterceptor(worker) {
   const promiseTable = new Map;
   workerTasks.set(worker, promiseTable);
-  worker.addEventListener("message", (event) => {
+  worker.onmessage = (event) => {
     const { id, value } = event.data;
     promiseTable.get(id)?.resolve(value);
     promiseTable.delete(id);
-  });
+  };
   return worker;
 }
 export {

jsr.json

@@ -1,5 +1,5 @@
 {
   "name": "@nesterow/offload",
-  "version": "0.0.2",
+  "version": "0.0.3",
   "exports": "./mod.ts"
 }

offload.ts

@@ -54,15 +54,12 @@ function createTaskCallback<T, E>(
 ): TaskCallback<T, E> {
   const cb = async function (data: E): Promise<T> {
     const id = createTaskId();
-    worker.addEventListener(
-      "error",
-      (event) => {
-        const error = event.message;
-        workerTasks.get(worker)?.get(id)?.reject(new OffloadError(error, id));
-        workerTasks.get(worker)?.delete(id);
-      },
-      { once: true },
-    );
+    const errorCallback = (event: ErrorEvent) => {
+      const error = event.message;
+      workerTasks.get(worker)?.get(id)?.reject(new OffloadError(error, id));
+      workerTasks.get(worker)?.delete(id);
+    };
+    worker.addEventListener("error", errorCallback, { once: true });
     const workerTask = Promise.withResolvers<T>();
     workerTasks.get(worker)?.set(id, workerTask);
     const request: WorkerRequest<E> = { id, params: data };
@@ -71,10 +68,12 @@ function createTaskCallback<T, E>(
       const result = await workerTask.promise;
       workerTasks.get(worker)?.delete(id);
       if (eof) eof();
+      worker.removeEventListener("error", errorCallback);
       return result;
     } catch (error) {
       workerTasks.get(worker)?.delete(id);
       if (eof) eof();
+      worker.removeEventListener("error", errorCallback);
       throw error;
     }
   };
@@ -155,14 +154,13 @@ function terminate<T, E>(cb: TaskCallback<T, E>): void {
 function createTaskId(): Id {
   return Math.floor(Math.random() * Number.MAX_SAFE_INTEGER);
 }
-
 function withMessageInterceptor(worker: Worker): Worker {
   const promiseTable: PromiseTable = new Map();
   workerTasks.set(worker, promiseTable);
-  worker.addEventListener("message", (event) => {
+  worker.onmessage = (event) => {
     const { id, value } = event.data as WorkerResponse<unknown>;
     promiseTable.get(id)?.resolve(value);
     promiseTable.delete(id);
-  });
+  };
   return worker;
 }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@nesterow/offload",
-  "version": "0.0.2",
+  "version": "0.0.3",
   "author": {
     "name": "Anton Nesterov",
     "url": "https://github.com/nesterow"