Yasir_Malik

Hello,
Can someone please explain to me how select() works? I don't understand how it handles multiple sockets. In fact, I don't understand how multiple clients can log onto to a server that only uses select() to handle the clients.

This is in relation to my DNS Message Format topic.
Thanks,
Yasir

Thantos

http://www.ecst.csuchico.edu/~beej/g...ed.html#select

Basically you setup a list of sockets to monitor. you then call select with this list as a parameter. select() simply checks to see if its avialable to be written to or read from depending on which parameter it is. If it is, it modifies the list and checks the next socket in the list.

When select is done you then step through the list and check to see if a particular socket is avialable and if it is you do whatever operator you wanna do.

variable

is select non-blocking, and does it work in windows?

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Thantos

select has a time out parameter. So technically it is blocking while its executing you can setup a low time out so it doesn't block for too long

It does work in windows.

azteched

*But there's better, more elegant methods available on Windows - select() is essentially there for portability.

Salem

> It does work in windows.
But it only works on socket descriptors.
The Unix/Linux version of select works on any descriptor (eg. stdin)

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variable

ah, ok; then would it be better to use asynchronous sockets winsock. if so, could someone send me a link to asynchonous winsock sockets. i read those beej tutorials, but he seems to concentrate on linux so no winsock.

thanks

__________________
"Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life."

"They say a little knowledge is a dangerous thing, but it's not one half so bad as a lot of ignorance."

"Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it."
[all]- Terry Pratchett

Thantos

Look at the links page at the top of the forum.

Yasir_Malik

I've used select() to monitor file descriptors ready for reading. I can't think of an example where I would monitor sockets ready for writing. Can someone please give me an example?

Thanks,
Yasir

azteched

When using non-blocking sockets, you'd monitor via select() or whatever, because there's no point in looping waiting for send() not to fail with EWOULDBLOCK.

Devil Panther

Can someone please post some code on how to setup the timeout value?

Thank you.

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Kybo_Ren

Beej gives great examples on how to use the timout parameter in slect() -- look in his site.

Thantos

man select

Devil Panther

you were talking only about the select() timeout?!

I thought you were talking about sockets in general, because I really need to find a way to set a timeout for connect()... that default one minute is killing me.

oh well, thanks anyway.

__________________
"I don't suffer from insanity but enjoy every minute of it" - Edgar Allen Poe

http://www.Bloodware.net - Developing free software for the community.

azteched

Make the socket non-blocking?