**used to define a stack **
npm install --save js-stack-utility
import defineStack from 'js-stack-utility'
context.testStack = new defineStack()
context.testStack.ready()
等待一个阻塞完成
context.testStack.setReady()
释放一个阻塞
async function boot(){
//do something immiditely
await context.testStack.ready()
//dosomething after timestamp A
}
//anywhere timestamp A
context.testStack.setReady()
context.testStack.setBlock()
恢复一个阻塞
context.testStack.destory()
销毁该阻塞实例