gen_tcp buffering

Sean Hinde <>
Fri Jan 9 15:11:00 CET 2004


On 8 Jan 2004, at 20:42, Eric Newhuis wrote:

> Does gen_tcp do any "user level" buffering of packets/binaries?  And 
> if it does then is there any way to report the number/size buffered?  
> For both send and receive?
>
>

There is a socket option called 'buffer' which allows you to control 
the size of this for receiving data - the driver will accumulate this 
much before passing it into erlang.

you should be able to get the value using inet:getopts(Sock, [buffer]). 
I have played with this option and it does seem to behave like this.

Erlang also does buffering on the output side. I seem to recall from a 
previous post that if the socket would block the driver buffers data up 
to a certain amount, after which the sending erlang process blocks 
until something gives!

The socket options high_watermark and low_watermark seem to be the 
things that control this, though at this point we are running into my 
ability to understand inet_drv.c rather than actual experimentation.

Hope this helps.

Sean




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