Tornado ProcessPoolExecutor:如何限制进程数

import tornado.ioloop
import tornado.web
from tornado.concurrent import Future
from tornado.process import cpu_count
from tornado.concurrent import run_on_executor
from concurrent.futures import ProcessPoolExecutor

class MyHandler(tornado.web.RequestHandler):
    executor = ProcessPoolExecutor(max_workers=cpu_count())

    @tornado.web.asynchronous
    @tornado.gen.coroutine
    def get(self):
        result = yield self.long_running_task()
        self.write(result)
        self.finish()

    @run_on_executor
    def long_running_task(self):
        # 长时间运行的任务代码
        return "Task completed"

if __name__ == "__main__":
    app = tornado.web.Application([(r"/", MyHandler)])
    app.listen(8888)
    tornado.ioloop.IOLoop.current().start()