Re: min-write-size for a UDP socket to be POLLOUT cannot be set. (proposed fixes)

[Ben Greear <greearb@candelatech.com>]

Richard B. Johnson wrote:

> On Mon, 10 Dec 2001, Ben Greear wrote:

>>I have 4M queue size.  I have 4M-2k bytes already in the
>>queue (2k free).  I have a 4k UDP buffer to write.  I call
>>select and it says the socket is writable.  However, in this
>>case I cannot actually write to the socket because I have only
>>2 of the 4k that I need...  Now, I can detect the failure to send
>>and re-transmit, but that basically gets me into a tight loop because
>>select keeps saying I can write, and I keep trying.  The tight loop
>>is doubly bad because the machine is already highly stressed or it's
>>buffers would never be so full....
>>
>>I want select to only say I can write when I'm at XX (say, 64k) bytes of
>>free buffer-queue space...
>>
>>Ben
>>
>>
> 
> If you have a 4M queue size, it appears as though you are trying to
> use UDP where TCP should have been used. Normally, what you call the
> queue size, is set to contain you largest packet you will ever want to
> send. With this in mind, you don't even know if a fragmented packet
> can be routed if it's more than 64k in length so you would never try
> to send something larger than that under UDP.


Assume that I actually want to do what I said I did! :)

I never try to send
a packet bigger than 64k, the protocol doesn't handle it.  But, I may try
to send 100000 60k UDP packets in very fast succession...which could fill up my
send queue.



-- 
Ben Greear <greearb@candelatech.com>       <Ben_Greear AT excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear