waitgroup.js

waitgroup.js

class WaitGroup {
  constructor(initial, opt_sab) {
    this._sab = opt_sab || new SharedArrayBuffer(4);
    this._wg = new Int32Array(this._sab);
    this.add(initial);
  }
  static connect(wg) { return new WaitGroup(0, wg._sab) }
  add(n) {
    let current = n + Atomics.add(this._wg, 0, n);
    if (current < 0) {
      throw new Error('WaitGroup is in inconsistent state: negative count.');
    }
    if (current > 0){ return }
    Atomics.notify(this._wg, 0);
  }
  done() { this.add(-1) }
  wait() {
    for (;;) {
      let count = Atomics.load(this._wg, 0);
      if (count == 0){ return }
      if (Atomics.wait(this._wg, 0, count) == 'ok') { return }
    }
  }
}