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import { nextTick } from "./deps.ts";
export class Semaphore {  private tasks: (() => void)[] = [];  count: number;
  constructor(count: number) {    this.count = count;  }
  private schedule() {    if (this.count > 0 && this.tasks.length > 0) {      this.count--;      const next = this.tasks.shift();      if (next === undefined) {        throw "Unexpected undefined value in tasks list";      }      next();    }  }
  /** returns current scheduled tasks length */  get length(): number {    return this.tasks.length;  }
  public acquire() {    return new Promise<() => void>((resolve) => {      const task = () => {        let released = false;        resolve(() => {          if (!released) {            released = true;            this.count++;            this.schedule();          }        });      };      this.tasks.push(task);      nextTick(this.schedule.bind(this));    });  }
  public async use<T>(fn: () => Promise<T>) {    const release = await this.acquire();    try {      const res = await fn();      release();      return res;    } catch (err) {      release();      throw err;    }  }}