src/vs/base/node/processes.ts/AbstractProcess/pid
class AbstractProcess:	public get pid(): Promise<number> {
		if (this.childProcessPromise) {
			return this.childProcessPromise.then(childProcess => childProcess.pid, err => -1);
		} else {
			return new Promise<number>((resolve) => {
				this.pidResolve = resolve;
			});
		}
	}