Zookeeper的读操作:getData()、getChildren()、exists(),都有可选参数watch。
Definition
watch是一次性事件,当watch监视的数据发生变化时就会被触发。
One-time trigger
当znode数据发生变化时,客户端会接收到一个watch事件。只有客户端读操作后,数据变化时服务端才会发送watch事件。后续服务端数据发生变化,客户端不会接收到watch事件,除非客户端第二次发起读操作。
Sent to client
这意味着事件可能不会到成功到达客户端,可能只在路上。watch是异步发送的,客户端在接收到watch事件时才出发watch里的操作。网络延时或其他因素会造成客户端在不同的时间内接收到watch和返回code的更新。
注意的时,客户端会看到的会保持一致性。
The Data for which watch was set
node改变有多种方式。这使得zookeeper维护两个watch列表。getData()和exists()对应data watch,getChildren()对应child watch。
使用何种watch是根据返回的data类型来决定的。getData()和exists()返回node的data,getChildren()返回子节点列表。
setData()会触发data watch。
Things to Remember about Watches
One time triggers,当你在收到一个watch event后,想再收到znode data的改变通知,就需要再次设置watch。
由于one time triggers和在接收watch和发送下一个watch之间的延时,会造成你无法可靠的知道Zookeeper znode每一次的data改变。
相关推荐
Store-Watches-and-jewlry
手表要运行此项目,您必须打开postgresql服务器。... 您可以将POST请求发送到以创建DB的新条目。 可接受的标头为“ Contenty-type:application / json”和“ Content-type:application / xml”。...
此功能利用了 Consul Watches 和一个名为 core-config-watcher 的简单工具。Consul Watches是一种指定数据视图(例如键/值对或运行状况检查)的方法,该视图会受到更新的监控。检测到更新时,将调用外部处理程序。...
be worn by a user, including clothing, watches, glasses, shoes and similar items. Wearable computing devices can range providing very specific, limited features like heart rate monitoring and ...
An Android inventory app for managing an inventory of premium watches. Users can add a new watch (using the " " FAB), edit details, add an image (using the "image" FAB) or delete a watch. Getting ...
Best File Explorer for Phones, Tablets, USB Storage, Root Storage, Cloud Storage, Chromecast, Wear OS Watches, Android TV and Chrome OS It is Simple, Small, Fast and Efficient File Explorer and One ...
Our e.MMC-Based MCPs do more than meet the memory requirements of mid-tier phones, tablets, auto infotainment systems and smart watches. They save more than 40% space versus discrete memory—reducing ...
watches, power banks, Bluetooth headsets, cameras, electric shavers, etc. Virtually anything that uses a rechargeable battery can be designed to use Qi wireless technology. However, Qi wireless power ...
The Arduino platform was developed keeping wearables, such as watches that track your location or shoes that count the miles you've run, in mind. It is basically an open-source physical computing ...
Wireless charging is also appearing in a growing number of other consumer product categories—smart watches, power banks, Bluetooth headsets, cameras, electric shavers, etc. Virtually anything that ...
It is used by all browsers on all screen sizes on all types of IoT devices, including phones, computers, video games, televisions, watches, kiosks, and auto consoles. Authors Eric Meyer and Estelle ...
• Connected watches • Advanced personal fitness devices • Interactive entertainment devices • Advanced Remote controls • Gaming controllers Applications • Bluetooth 5 data rate support: 2 Mbs, 1...
Devices like mobile phones, PDAs, laptops, desktops, calculators, watches, keyboards, mice, printers, scanners, cameras, and video game consoles are just a sample of what device manufacturers will be...
语言:English 购买智能手表为男人支票价格并在线购买。 还阅读了最新的智能手表评论 男士智能手表:以最优惠的价格在线购物智能手表。 选择各种各样的男性智能手表。 从电视到空调,甚至灯泡,每隔一个小工具现在都...
consoles, ATMs, smart watches, to even glasses! C++ programmers will never be short of work. I hope you find this book an invaluable resource in your journey to learning the C++ programming language.
It is used by all browsers on all screen sizes on all types of IoT devices, including phones, computers, video games, televisions, watches, kiosks, and auto consoles. Authors Eric Meyer and Estelle ...
FileSpy is an open source program that watches and logs files that has changed, deleted, created, and renamed. Most likely use of this is to tell when your computer has downloaded spywares from the ...
语言:English 为了满足不断增长的市场的需求,男孩中提供了种类繁多的设计。 一站式提供如此出色的产品,Artodays一定可以满足您的所有时尚需求。 因此,只需单击几下,即可为男孩购买这些手表中的任何一个。...
Create React App入门 该项目是通过引导的。 可用脚本 在项目目录中,可以运行: yarn start 在开发模式下运行应用程序。 打开在浏览器中查看它。 如果您进行编辑,则页面将重新加载。 您还将在控制台中看到任何...