Hallo, Brett!

*** Am Dienstag 09. Juli 1996 um 14:07 schrieb Brett Maxfield an Thomas Seeling:

 TS>> find out the hostname, but you should be aware that gethostbyaddr is
 TS>> not threadsafe from my experience (tcp/ip 2.0 and un64092). Therefore
 TS>> a mutex semaphore should be used to encapsulate the call.

 BM>  I am not yet fully familiar with threads.. but 'not theadsafe' would
 BM>  mean non-reeentrant among threads of a single task? This would be ok as
 BM>  each thread would have be given a socket fd, and a hostname or maybe
 BM>  a struct with any miscelleneous connection info by it's controlling
 BM>  task.
threadsafe means that multiple threads can concurrently call the same
function and be successfull.

This is not the case if the function uses static data structures. A
prominent example is strtok(), as you might know.

gethostbyaddr() suffers from the same problem. You call it and receive a
pointer to static data as return result. As soon as the next call happens,
the data is corrupt in respect to what the first caller expects.

Protect the call with a mutex semaphore, copy the data and then release the
semaphore.

 BM>  Most likely i will have a server process, with each connection having
 BM>  a thread which is given the socket fd for that connection. The thread
 BM>  could then exit asynchronously when the connection died. It would then
 BM>  be responsible for freeing the passed socket and ending it's thread,
 BM>  when the connection was complete.
That's the usual approach.

 BM>  The only other thing is, how does the thread then control the status of
 BM>  the connection, ie. detect when the connection has been lost, or if it
 BM>  decides that the connection has to be closed.
Either you receive a SIG_PIPE, or the read/write call returns with an
return code indicating the problem (rc==-1 and errno set or similar
things).


Tschau...Thomas

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