Can PHP Effectively Implement Real-Time Chat Using Comet Technology?

Comet in PHP: Challenges and Solutions

Implementing real-time chat using PHP's backend can pose certain challenges, particularly with regard to Comet technology. Concerns have been raised about PHP's limitations for this purpose, as Comet requires persistent connections to each browser client.

Traditionally, using Apache's mod_php meant that each client would occupy an Apache child full-time. This presents scalability issues, as handling numerous simultaneous connections can become overwhelming.

While FastCGI may appear to be a potential solution, it falls short in addressing the underlying issue. Specifically, each incoming request to Apache occupies a worker thread until it completes, which can be an extended period in a Comet context.

Additionally, PHP itself limits the use of Comet, as it lacks the necessary functionality to resume comet requests when the triggering event occurs. Continuations, which provide this ability, are not supported in PHP. The only known implementation of this feature is found in Java-based servers like Apache Tomcat.

As a potential workaround, it has been suggested to utilize a load balancer (e.g., HAProxy) to distribute incoming requests between Apache and a Comet-enabled server (e.g., Java-based) that can handle persistent connections more effectively.

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