feat(tasks): adds parallel transform

src/tasks/transform/index.ts

@@ -1,3 +1,4 @@
 export * from './context';
+export * from './parallel';
 export * from './select';
 export * from './series';

src/tasks/transform/parallel.ts

@@ -0,0 +1,40 @@
+import { Task, Context } from '../../definitions';
+import { run } from '../consume/run';
+import { log } from '../create/log';
+import { Empty, NullaryFn } from 'type-core';
+import { into } from 'pipettes';
+
+export function parallel(...tasks: Array<Task | Empty>): Task.Async {
+  return async (ctx: Context): Promise<void> => {
+    into(ctx, log('debug', 'Run tasks in parallel'));
+
+    const cbs: NullaryFn[] = [];
+    function cancel(): void {
+      while (cbs.length) {
+        const cb = cbs.shift();
+        if (cb) cb();
+      }
+    }
+
+    ctx.cancellation.finally(() => cancel());
+
+    try {
+      await Promise.all(
+        tasks.map((task, i) => {
+          return task
+            ? run(task, {
+                ...ctx,
+                route: ctx.route.concat(i),
+                cancellation: new Promise((resolve) => {
+                  cbs.push(resolve);
+                })
+              })
+            : Promise.resolve();
+        })
+      );
+    } catch (err) {
+      cancel();
+      throw err;
+    }
+  };
+}