add event and pool structures

src/lib.ts

@@ -9,3 +9,5 @@ export { log_from, next, split_promise, wait } from "./lib/utils.ts";
 export { Chain } from "./lib/Chain.ts";
 export { Channel } from "./lib/Channel.ts";
 export { Range, range } from "./lib/Range.ts";
+export { Event } from "./lib/Event.ts";
+export { AsyncPool } from "./lib/AsyncPool.ts";

src/lib/AsyncPool.ts

@@ -0,0 +1,23 @@
+import { Event } from "./Event.ts";
+
+export class AsyncPool {
+	limit;
+	current = 0;
+	current_changed = new Event<void>();
+
+	constructor(limit: number = 8) {
+		this.limit = limit;
+	}
+
+	async run(task: () => unknown) {
+		while (this.current >= this.limit) await this.current_changed.wait();
+		this.update_current(+1);
+		await task();
+		this.update_current(-1);
+	}
+
+	update_current(increment: number) {
+		this.current += increment;
+		this.current_changed.trigger();
+	}
+}

src/lib/Event.ts

@@ -0,0 +1,27 @@
+import { split_promise } from "../lib.ts";
+
+export class Event<V> {
+	subscriber = [] as ((value: V) => unknown)[];
+
+	subscribe(callback: (value: V) => unknown) {
+		this.subscriber.push(callback);
+	}
+
+	unsubscribe(callback: (value: V) => unknown) {
+		const index = this.subscriber.indexOf(callback);
+		if (index === -1) return false;
+		this.subscriber.splice(index, 1);
+		return true;
+	}
+
+	trigger(value: V) {
+		for (const handler of this.subscriber) handler(value);
+	}
+
+	async wait() {
+		const [promise, resolver] = split_promise<V>();
+		this.subscribe(resolver);
+		await promise;
+		this.unsubscribe(resolver);
+	}
+}