write_event called very infrequently during reproxy, causing lots of perlbal_timeouts

[Eric Lambrecht]

We had an issue here where numerous downloads that perlbal was proxying 
out to our users (from mogile, *natch*) were getting cut off for some 
reason.

After turning on debugging, it appears the 'alive_time' field in 
Perlbal::Socket wasn't being updated, and so the ClientProxy object was 
being closed by the Socket::_do_cleanup() idle socket closer.

I see that 'alive_time' should be updated every time 
ClientProxy::event_write() is called, but when I turn on debugging I 
find that that method gets called very rarely while reproxying files. It 
happens so rarely that 'alive_time' doesn't get updated every 30 
seconds, _do_cleanup closes the socket, and our downloads get cut off.

I hacked together a solution by writing a Perlbal::Socket::write() 
method that updates alive_time before calling Danga::Socket::write(), 
and that seems to solve things, but I'm not certain it is correct (does 
just writing to the socket imply it is still alive?).

Anybody else ever experience this problem?

Eric...