Merge pull request #16 from johnsonjo4531/master

Optimize Transferables

Author: developit

.gitignore

@@ -1,3 +1,4 @@
 /dist
 /node_modules
 /package-lock.json
+/npm-debug.log

README.md

@@ -48,6 +48,12 @@ console.log(await getName('developit'))
 
 [🔄 **Run this example on JSFiddle**](https://jsfiddle.net/developit/mf9fbma5/)
 
+
+## Transferable ready
+
+Greenlet will even accept and optimize [transferables](https://developer.mozilla.org/en-US/docs/Web/API/Transferable) as arguments to and from a greenlet worker function.
+
+
 ## Browser support
 
 Thankfully, Web Workers have been around for a while and [are broadly supported](https://caniuse.com/#feat=webworkers) by Chrome, Firefox, Safari, Edge, and Internet Explorer 10+.
@@ -62,7 +68,6 @@ if (window.Worker) {
 }
 ```
 
-
 ## License & Credits
 
 > In addition to the contributors, credit goes to [@sgb-io](https://github.com/sgb-io) for his annotated exploration of Greenlet's source. This prompted a refactor that clarified the code and allowed for further size optimizations.

greenlet.js

@@ -5,7 +5,7 @@
 export default function greenlet(asyncFunction) {
 	// Create an "inline" worker (1:1 at definition time)
 	let worker = new Worker(
-			// The URL is a pointer to a stringified function (as a blob object)
+		// The URL is a pointer to a stringified function (as a blob object)
 			URL.createObjectURL(
 				new Blob([
 					// Register our wrapper function as the message handler
@@ -17,9 +17,15 @@ export default function greenlet(asyncFunction) {
 								userFunc.apply.bind(userFunc, userFunc)
 							).then(
 								// success handler - callback(id, SUCCESS(0), result)
-								d => { postMessage([e.data[0], 0, d]); },
+								// if `d` is transferable transfer zero-copy
+								d => {
+									postMessage([e.data[0], 0, d], (
+										d instanceof ArrayBuffer ||
+										d instanceof MessagePort ||
+										d instanceof ImageBitmap) ? [d] : []);
+								},
 								// error handler - callback(id, ERROR(1), error)
-								e => { postMessage([e.data[0], 1, ''+e]); }
+								er => { postMessage([e.data[0], 1, '' + er]); }
 							);
 						}
 					) + ')(' + asyncFunction + ')'  // pass user-supplied function to the closure
@@ -48,14 +54,19 @@ export default function greenlet(asyncFunction) {
 	};
 
 	// Return a proxy function that forwards calls to the worker & returns a promise for the result.
-	return function(args) {
+	return function (args) {
 		args = [].slice.call(arguments);
-		return new Promise(function() {
+		return new Promise(function () {
 			// Add the promise controller to the registry
 			promises[++currentId] = arguments;
 
 			// Send an RPC call to the worker - call(id, params)
-			worker.postMessage([currentId, args]);
+			// The filter is to provide a list of transferables to send zero-copy
+			worker.postMessage([currentId, args], args.filter(x => (
+				x instanceof ArrayBuffer ||
+				x instanceof MessagePort ||
+				x instanceof ImageBitmap
+			)));
 		});
 	};
-}
+}