Note: In practice, most React apps only call FinRL 入门指南 ReactDOM.render() once. In the next sections we will learn how such code gets encapsulated into stateful components. We recommend that you don’t skip topics because they build on each other.
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React Without JSX
JSX is not a requirement for using React. Using React without JSX is especially convenient when you don’t want to FinRL 入门指南 set up compilation in your build environment.
For example, this code written with JSX:
can be compiled to this code that does not FinRL 入门指南 use JSX:
The component can either be provided as a string, or as a subclass of React.Component , or a plain function for stateless components.
If you get tired of typing React.createElement so much, one common pattern is to assign a shorthand:
If you use this shorthand form for React.createElement , it can be almost as convenient to use React FinRL 入门指南 without JSX.
Alternatively, you can refer to community projects such as react-hyperscript and hyperscript-helpers which offer a terser syntax.
Elements are the smallest building blocks of React apps.
An element describes what you want to see on the screen:
Unlike browser DOM elements, React elements are plain objects, and are cheap to create. React DOM takes care of updating the DOM to match the React elements.
One might confuse elements with a more widely known concept of “components”. We will introduce components in the next section. Elements are what components are “made of”, and we encourage you to read this section before jumping ahead.
Rendering an Element into the DOM
Let’s say FinRL 入门指南 there is a somewhere in your HTML file:
We call this a “root” DOM node because everything inside it will be managed by React DOM.
Applications built with just React usually have a single root DOM node. If you are integrating React into an existing app, you may have as many isolated root DOM nodes as you like.
To render a React element into a root DOM node, pass both to ReactDOM.render() :
It displays “Hello, world” on the page.
Updating the Rendered Element
React elements are immutable. Once you create an element, you can’t change its children or attributes. An element is like a single frame in a movie: it represents the UI at a certain point in time.
With our knowledge so far, the only way to update the UI is to create a new element, and pass it to ReactDOM.render() .
Consider this FinRL 入门指南 ticking clock example:
It calls ReactDOM.render() every second from a setInterval() callback.
In practice, most React apps only call ReactDOM.render() once. In the next sections we will learn how such code gets encapsulated into stateful components.
We recommend that you don’t skip topics because they build on each other.
React Only Updates What’s Necessary
React DOM compares the element and its children to the previous one, and only applies the DOM updates necessary to bring the DOM to the desired state.
You can verify by inspecting the last example with the browser tools:
Even though we create an element FinRL 入门指南 FinRL 入门指南 describing the whole UI tree on every tick, only the text node whose contents has changed gets updated by React DOM.
In our experience, thinking about how the UI should look FinRL 入门指南 at any given moment rather than how to change it FinRL 入门指南 over time eliminates a whole class of bugs.
Load balancing in FinRL 入门指南 Orleans
Load balancing, in a broad sense, is one of the pillars of the Orleans runtime. Orleans runtime tries to make everything balanced, since balancing allows to maximize resource usage and avoid hotspots, which leads to better performance, as well as helps with elasticity. Load balancing in Orleans applies in multiple places. Below is a non-exhaustive list of places where the runtime performs balancing:
Default actor placement strategy is random - new activations are FinRL 入门指南 placed randomly across silos. That results in a balanced placement and prevents hotspots for most scenarios.
A more advanced ActivationCountPlacement FinRL 入门指南 tries to equalize the number of activations on all silos, which FinRL 入门指南 results in a more even distribution of activations across silos. This is especially important for elasticity.
Grain Directory service is built on top of a Distributed Hash Table, which inherently is balanced. The directory service maps grains to activations, each silo owns part of the global mapping table, and this table is globally partitioned in a balanced way across all silos. We use consistent hashing with virtual buckets for that.
Clients connect to all gateways and spread their requests across them, in a FinRL 入门指南 balanced way.
Reminder service is a distributed partitioned runtime service. The assignment of which silo is responsible to serve which reminder is balanced across all silos via consistent hashing, just like in grain directory.
Performance critical components within a silo are partitioned, and the work across them is locally balanced. That way the silo runtime can fully utilize all available CPU cores and not create in-silo bottlenecks. This applies to all local resources: allocation of work to threads, sockets, dispatch responsibilities, queues, etc.
StreamQueueBalance balances the responsibility of pulling events from persistence queues FinRL 入门指南 across silos in the cluster.
Also notice that balancing, in a FinRL 入门指南 broad sense, does not necessarily mean loss of locality. One FinRL 入门指南 can be balanced and still maintain a good locality. For example, when balancing means sharding/partitioning, you can partition responsibility for a certain logical task, while still maintaining locality within each partition. That applies both for local and distributed balancing.
Refer to this presentation on Balancing Techniques in Orleans for more details.
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