Long Polling

Long polling, also known as Comet, puts the server in control, by making the client wait for responses.

Long polling也就是我们熟知的Comet，其让服务器来控制这些事，让客服端等在那里听服务器的响应。

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This means you can give regular requests a short lifetime, but you can also extend this lifetime to several minutes for a mechanism that responds to long polling requests.

这意味着可以给常规的请求设置很短的生命周期，但是对于响应长轮询请求的机制，也可以将这个生命周期延长至几分钟。

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In a long polling request, a client sends a request to a server to retrieve available information.

在长轮询请求中，客户机向服务器发出一个请求来检索可用信息。

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As mentioned, our application is using long polling, so our polling endpoint is going to handle the polling requests from the clients and respond with new chat messages as they are sent to the server.

前面已提到，我们的应用程序使用的是长轮询，所以轮询端点将处理来自客户端的轮询请求，使用它们发送到服务器的新聊天消息作为响应。

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Both Bayeux and WebSockets attempt to avoid the resource limits by using a fall-back mechanism for long polling ( in the case of Bayeux) or switching to a non-HTTP based secondary protocol instead.

Bayeux和WebSockets都试图避免资源限制问题，使用回退机制来实现长轮询（比如Bayeux），或者切换到其他非HTTP协议之上。

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Bayeux implementations support a specific HTTP method called long polling.

Bayeux实现支持一种名为长轮询的特定HTTP方法。

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Fetching messages is no longer using AJAX or long polling. You receive a message while the message is sent to you.

消息的获取不再用AJAX轮询，而是在发送消息的同时将消息直接发送给相关的用户，不必用户自己去取了。

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For example an RTMP channel could be specified, but if that connection fails it could fail back to a long polling channel.

例如，可以指定RTMP管道，但如果该连接失败，就回到长轮询管道。

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On the client side, broadcasting will make all long polling requests to complete the sent message, and another long polling request is immediately sent to receive the next events.

在用户端，广播会让所有的长轮询请求来完成消息发送，并且会立即发送另一个长轮询请求来接收下一个事件。

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The client code is always the same; it's the same code used in Parts 1, 2, and 3 of this series ( in the chat samples using Comet long polling).

客户端代码始终保持不变；与本系列第1部分、第2部分、第3部分文章中所用的代码相同（都位于使用Comet长轮询的聊天样例代码中）。

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With long polling, the client requests information from the server in a manner that is similar to traditional polling.

对于长轮询，客户机以与传统轮询类似的方法向服务器请求信息。

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Long polling does exactly what it sounds like it does: It polls the server, and sometimes the response to the poll will take a long time.

长轮询的含义与它的字面意思并不完全相同：它轮询服务器，有时需要很长时间才能获得轮询的响应。

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We are hopeful that websocket usage will be able to give us even better throughput and latency for cometd than the already impressive results achieved with long polling.

我们真心希望WebSocket可以给我们更大的吞吐量和更低的延迟，比现在已经让人印象深刻的长轮询要更好。

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In long polling, however, a client would have an outstanding request to the server at any point of time.

然而，在长轮询中，一个客户机可能需要随时向服务器发送一个重要请求，因此，服务器再一次需要为每个客户机准备一个或多个线程。

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Long polling is a polling technique in which the server will delay completing the HTTP response until either an update is ready for the client or a timeout occurs.

长轮询是一种轮询技术，其中服务器延迟完成HTTP请求，直至已经为客户机准备好了一个更新信息或发生超时。

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Part 1 introduced Reverse Ajax, polling, streaming, Comet, and long polling.

反向Ajax，第1部分：Comet简介介绍了Reverse Ajax、轮询、流、Comet和长轮询。

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The clients can create topics and submit messages to them through a RESTful API, while other clients subscribe to multiple topics through HTTP long polling.

客户端可以创建主题，并通过RESTful的API向它们提交消息，而其它客户端会通过HTTP的长轮询机制（long polling）来订阅多种主题。

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The publish/ subscribe mechanism was discussed, along with some background on why long polling is used for Web messaging.

文中讨论了发布/订阅机制，以及将长轮询用于Web消息传递的一些幕后原因。

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This is similar to long polling in that there is no latency.

和长轮询一样，这种方式也没有延时。

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At this point you might be thinking that there is a major problem with both long polling and streaming.

至此，您可能会想，长轮询和流都有一个很大的问题。

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Long Polling: Also known as Asynchronous Polling, this method is a hybrid of pure server push and client pull.

长时间轮询：也就是所谓的异步轮询，这种方式是纯服务器端推送方式和客户端拉取方式的混合。

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The most common "true" Comet technique is a variant of polling called long polling.

最常见的“真正的”Comet技术是轮询的一种变体，即长轮询（long polling）。

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You learned how Comet using HTTP long polling is the best way to reliably implement Reverse Ajax, since all browsers now provide support.

您应该已经了解到，使用HTTP长轮询的Comet是可靠地实现反向Ajax的最佳方式，因为现在所有浏览器都提供了这方面的支持。

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There are two basic types of polling channels, short and long polling.

有两种基本的轮询管道：短轮询与长轮询。

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An alternative to this technique is long polling, which can avoid both these problems.

该技术的另一种方案就是长轮询，可以避免这两个问题。

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The main difference between polling and long polling is how long it takes the server to respond.

轮询与长轮询之间的主要区别在于服务器花多长的时间作出响应。

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This way, you won't make the error of increasing all timeouts to facilitate long polling and then end up with unexpected trouble when regular requests keep hanging without being terminated like they're supposed to.

这样，您就不会犯下为了方便长轮询而延长所有超时的错误。当常规的请求没被恰当地终止并保持挂起时，这种错误会导致意外的麻烦。

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There have been three kinds of technology programs, namely polling, long polling and streaming mode, and appears based on these programs related to development framework.

目前有三种技术方案，即轮询，长轮询和流方式，并且出现了基于这些基础框架的开发框架。

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Another common technique is long polling.

另一个常见的技巧是长轮询。

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Shibley telhami, of the University of Maryland who has long experience in polling regional opinion, notes two trends.

马里兰大学的希布利泰尔哈米（shibley telhami）在调查地区民意方面经验丰富，他认为存在两个趋势。

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