UDP programming

Hi! I have some doubts about UDP programming. I´ve been trying to find answers, but could´t find :( . Any link or response is much appreciated!

1) Can I send and receive using the same socket in multithread? Must I use semaphores?

2) If two hosts send something at the same time, both the datagrams will be sent, or they will be dropped? I know that UDP is a little unreliable, but can this kind of error occur, or Ethernet protocol deals with it?

Again, thanks any help. :)

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Originally Posted by Mortissus

2) If two hosts send something at the same time, both the datagrams will be sent, or they will be dropped? I know that UDP is a little unreliable, but can this kind of error occur, or Ethernet protocol deals with it?

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Do you mean 2 hosts each sending a datagram to each other? In that case both would be receiveve each others datagram.

To the first question:

You don't need external synchronization just to send() and recv() in multiple threads on the same socket, but you'll likely sync. some at some point.

Thanks for the answer!

I will try to better explain the second question. Is UDP safe against collision (physical level)? I need to know what kind of errors can I have with UDP, that I do not have with TCP, besides datagrams dropped and arriving out of order. What I must consider when programming UDP, that I do not need to worry with TCP.

As always, thanks any kind of help. :)

Other then datagrams ariving out of order and being dropped they can be corupted or duplicated.
If both hosts send a datagram they wont collide, the router(s) will still foreward both allthoug neither is guaranteed to arive and each host may not receive the others datagram at EXACLY the same time.

Ok! Thanks very much! :)