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ieuan25 / HttpServer

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Use select() IO multiplexing system call for timeouts. #7

Open kybu opened 10 years ago

kybu commented 10 years ago

As we spoke, have a look at select(). It should be mentioned in "14.4.1 select and pselect functions" in the "14. Advanced I/O" chapter.

Just re-implement alarm() in this task.

ieuan25 commented 10 years ago

I've added this now (see latest commit here https://github.com/ieuan25/HttpServer/commit/cbd0757c1a72dc7c973c4f492526b90dd273b7be).

Two questions.

I noticed first that I was terminating the process when select returned -1 (error condition). This was a problem because it does this when interrupted by signals and my SIG_CHLD signals were causing this to happen. Therefore no longer worrying about this error condition. I noticed though that this has never happened to me before with the accept function. Is this because accept is re-entrant meaning default behaviour is to re-start when interrupted by a signal?

Also, as you can see I'm not setting the file descriptors to non-blocking when doing the accept/read/write as I'm assuming that they will not block given the result of select. Is this sufficient or should I also set them to non-blocking even though I won't even execute them unless select says they won't block?

kybu commented 10 years ago
  1. I believe select() and accept() behave the same way in this situation. Also, your SIGCHLD handler has SA_RESTART set so they should not return -1 and set errno to EINTR. That can happen for any other signal though. Bear in mind that we haven't done any process / thread signal masking yet. Check the log file and see what errno caused it, it should be logged. The exception contains its value.
  2. What you are saying is generally true but it might be different in the design you have there. Let me check that and I will get back to you later.