I have a isapi filer and I want to add a logic based on the incoming domain ( my server farm hosts many domains). There domain list is dynamic , I can export these domain list into a text file and read it from the isapi , but is there a way to keep this file in memory (is array or linked list) to save the IO call. similar to global application state .
How are your worker processes distributed across your servers? Do you have one server with one worker process, or multiple servers?
If you have one server with one worker process, you can just read the file into a static array or string to manage it (just make sure you account for concurrent threads reading/modifying it simultaneously)
If you have multiple worker processes on just one server, you can use named shared memory. I've used this before in ISAPI filters to share information, and it works pretty well. It should even take care of concurrency for you. You can read more here: http://msdn.microsoft.com/en-us/library/aa366551%28v=vs.85%29.aspx
If you're spread across multiple servers, you could use a distributed cache like memcached. This is more complex to set up, but it'll give you good performance. There's a thread on setting this up here: C++ api for memcache