Polling, long polling, long connection, Flash Socket

1. Polling: The client regularly sends Ajax requests to the server, and the server immediately returns response information and closes the connection after receiving the request.
   Advantages: It is easier to write back-end programs.
   Disadvantages: Most of the requests are useless, wasting bandwidth and server resources.
   Example: Suitable for small applications.
2. Long polling: The client sends an Ajax request to the server. After receiving the request, the server holds the connection until there is a new message and then returns the response information and closes the connection. After the client processes the response information, it sends a new one to the server. ask.
   Advantages: There will be no frequent requests when there is no message.
   Disadvantage: Server hold connection consumes resources.
   Examples: WebQQ, Hi web version, Facebook IM.

In addition, there is also a distinction between long connections and socket connections:

1. Long connection: embed a hidden iframe in the page, set the src attribute of the hidden iframe to a request for a long connection, server side Just continuously input data to the client.
   Advantages: Messages arrive immediately and no useless requests are sent.
   Disadvantages: Maintaining a long connection by the server will increase overhead.
   Example: Gmail chat
2. Flash Socket: Embed a Flash program using the Socket class in the page. JavaScript communicates with the server-side Socket interface by calling the Socket interface provided by this Flash program. JavaScript receives the server-side transmission Control the display of the page after the information.
   Advantages: Real instant communication, not pseudo-instantaneous communication.
   Disadvantages: The client must install the Flash plug-in; it is not an HTTP protocol and cannot automatically traverse the firewall.
   Example: Internet interactive game.

The above is an introduction and comparison of the advantages and disadvantages of the four request methods.

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The above has introduced polling, long polling, long connection, and Flash Socket, including all aspects of it. I hope it will be helpful to friends who are interested in PHP tutorials.