Is select() Ok to implement single socket read/write timeout?

I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket.

Select is known to be inefficient wh开发者_如何学JAVAen dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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Yes that's no problem, and you do want some timeout mechanisms to not leak resources from bad behaving clients etc.

Note that having a large number of threads is even more inefficient than having select dealing with a large number of sockets.

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If yo uthink select is inefficient with a large number of sockets, try handling a large number of sockets with one thread per sockt. You are in for a world of pain. Like you will have problems scaling to 1000 threads.

What I have done in the past is that:

• Group sockets in groups of X (512, 1024).
• Have one thread or two run along those groups and select () - then hand off the sockets with new data into a queue.
• have a number of worker threads work off those sockets with new data. How many depends how much I need to max out the CPU ;)

This way I dont ahve a super über select () with TONS of items, and I also dont waste ridiculous amountf of memory on threads (hint: every thread needs it's own stack. With ONLY 2mb, that is 2gb for 1000 sockets - talk about inefficient) and waste hugh amounts of CPU on doing useless context switches.

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The question with threads/select is whether you want to avoid clients blocking each other. If this is not an issue, then work single-threaded. If it is, choose an appropriate threading scheme (1 thread per connection, worker threads per connection, worker thread per request,...).

When working with 1 thread per connection, a select per read/write is a decent solution, but generally speaking, it is better to work with non-blocking sockets in combination with select to avoid blocking in situations where only a part of the expected message arrives and then do a select after writing.