[erlang-questions] Unbuffered/blocking gen_tcp send

[David Sveningsson]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Matthias Lang wrote:
> Hi,
> 
>> Hi, is it possible to have gen_tcp:send block until the receiver has
>> received the package using gen_tcp:recv? For instance if the sender
>> transmits packages which takes long time to process for the receiver.
> 
> gen_tcp:send can't do this for you. More generally, TCP doesn't provide
> that service. (And: TCP's interface upwards is streams, not packets. The
> packets you get from the {packet, N} modes in gen_tcp are added by Erlang
> on top of TCP)
> 
>> I've been experimenting with the buffer sizes but even setting to sndbuf
>> and recbuf to 1 won't make gen_tcp:send to block, unless the packages
>> are large (1Kb+).
> 
>> I guess it would be possible to manually implement flow-control by
>> acknowledging each package but I would rather just have gen_tcp:send block.
> 
> You've got the right idea. TCP has flow control, but it can't be
> controlled at the fine level you would like it to, i.e. down to
> whether a given "packet" has been received by an application at the
> other end or not. If you want that, you have to implement it yourself
> on top of TCP.
> 
> Matthias

Ok, thanks.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.11 (Darwin)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAknomSkACgkQ6pa1H/H5pqWeDwCeN09xjkGiw77WCtluWi34r06t
1s8An344zRDJfmGMIPP4sHZpwTHL7o8M
=rcwp
-----END PGP SIGNATURE-----