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HTTP is historically request-response-driven. This means a server is idle as long as no-one asks it to do something. Typically fetching data or accepting some form. In reality, we’d often like to receive data from the server without any request. Typically to subscribe for some server-side updates. For example, displaying a current price on the stock exchange that changes many times per second. Or when waiting for some asynchronous process to complete. Traditionally this could be achieved with a few hacks. The most obvious and the worst one is busy-waiting. You simply keep asking the server over and over again periodically. More frequent requests result in a lot of excessive network traffic. Less frequent requests increase latency, so it’s no longer real-time communication.
A slightly smarter approach is long-polling. In this implementation, you periodically ask the server whether there is some new data. To avoid excessive round-trips, the server doesn’t respond until some update is available. Or, after a timeout, it sends back an empty response and the loop continues.
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Jest to odcinek podkastu:
Around IT in 256 seconds
Podcast for developers, testers, SREs... and their managers. I explain complex and convoluted technologies in a clear way, avoiding buzzwords and hype. Never longer than 4 minutes and 16 seconds. Because software development does not require hours of lectures, dev advocates' slide decks and hand waving. For those of you, who want to combat FOMO, while brushing your teeth. 256 seconds is plenty of time. If I can't explain something within this time frame, it's either too complex, or I don't understand it myself.
By Tomasz Nurkiewicz. Java Champion, CTO, trainer, O'Reilly author, blogger
Kategorie:
Technologia
Technologia