Under Apache, is it possible to run a single CGI process that can handle concurrent requests?
Using ISAPI, you can have a single multi-threaded process that efficiently handles concurrent requests. One very obvious benefit to a single application instance is that it can contain a single cache of data, for instance; a huge lookup table stored in RAM.
With FastCGI (or CGI), a single exe will only handle a single incoming request; not concurrent requests. This means that you'd have to have multiple FastCGI instances running to handle multiple concurrent requests. This also means that each FastCGI instance would need a copy of the huge lookup table; thus causing concern for memory consumption (due to duplication) as well as time wasted loading each copy of the cached data for each process.
[UPDATE]
After looking at the Apache online documentation, I found that the capability that I asked about in my post above can be accomplished by writing an Apache Module.
Apache modules directly hook into the Apache Server but this interface is way too raw (as it should be) to develop a web application as described above.
Assume that a person has experience writing CGI web applications in C or C++. Running your application as a CGI or a FastCGI application should run fine as a single threaded application in many if not most circumstances.
But if you decide to port your C/C++ web application to run as a module, you will need to build a thread pooled infrastructure for your web application logic to execute under.
Does anyone know of an existing Apache Module threaded framework that can be leveraged for developing web applications in C/C++?
FastCGI is not inherently single-threaded. Your FastCGI process can call accept on multiple threads and process them.