Merge pull request #4 from simon-liubin/develop

Develop
Merge pull request #5 from simon-liubin/develop

Develop
Executor 不持有线程池
isCanceled -> isCancelled
Merge pull request #6 from simon-liubin/update/executor

Executor 不持有线程池
Merge pull request #7 from simon-liubin/fix/cancelled

isCanceled -> isCancelled