In short, I think the concept of long HTTP connections in javascript really revolves around a communication style called COMET. This can be achieved in several different ways, but essentially involves a client (using XmlHttp privileges) requesting data from the server immediately, and the server refuses to respond until an event triggers it. After receiving this response, the client immediately makes another request (which will again hang on the server until something requires sending). This simulates a click on the server, but in fact it is nothing more than a delayed response used in a smart way. In the worst case, there may be a fairly high latency (i.e., 2 messages are required, so the cycle should be repeated twice taking into account all costs), but in general, if the message exchange rate is lowIt gives a reasonable idea of real time time.
, concurrency . , , .