Threads and TCP/IP

[Kevin D. Clark]

Cole Tuininga writes:

> Is it legitimate to have the two threads doing their respective
> operation on the socket simultaneously?  In other words, can you
> simultaneously read and write a tcp/ip socket?  Or would the threads
> need to do some locking themselves to make sure this doesn't happen?

[I assume that you're asking about some non-ancient version of Linux]


Yes, this is legal.  How could you know this?  If you were to dig a
little bit, you could find that the GNU C library conforms to the
POSIX.1 standard, and this standard dictates that both read() and
write() be thread-safe.  So, you don't need to perform any locking in
order to use sockets in this manner.

[I also assume that you are referring to stream and datagram sockets.
I wouldn't be surprised if some esoteric protocol implementations had
some warts in this area.  Caveat programmer.]

I have written an extensive amount of pthreads/socket code that uses
exactly this feature on a couple of platforms.  Because these
platforms conformed to POSIX.1, I was confident that this technique
would work (and, it in fact did work...)

Regards,

--kevin
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