[erlang-questions] gen_tcp send blocks gen_tcp recv.

Joseph Wayne Norton <>
Tue Sep 4 10:07:20 CEST 2012


Satyam -

The UBF framework may offer some examples for building a server, client, and protocol driver:

generic socket server:
    https://github.com/ubf/ubf/blob/master/src/proc_socket_server.erl

generic protocol driver:
    https://github.com/ubf/ubf/blob/master/src/contract_driver.erl

There is some documentation that describes how the framework works at a high-level:
   http://ubf.github.com/ubf/ubf-user-guide.en.html

Hope this helps.

- Joe N.

On Sep 4, 2012, at 4:45 PM, Satyam Shekhar <> wrote:

> @erik: I wasn't sure if this was the standard practice. Also, this complicates the architecture. Now, I ll have 2 processes, that manage a tcp socket. One for receiving and one for sending, both having reference to the same socket. Is this ok?
> 
> @arun: The article on trapexit only show how to do async accept. It doesnt do async send of gen_tcp socket. 
> To elaborate on the problem - I have one process that is an abstraction over the gen_tcp socket. It does xml parsing on the data received on the tcp socket and forwards parsed data to the controlling process. Also it receives the xml from a process and sends it on the tcp socket. Lets call this smart socket. Now, if the process that sends data to  smart socket, sends too much of it, smart socket starts to starts blocking on send calls.
> 
> How do people usually handle such scenarios?
> 
> 
> On Mon, Sep 3, 2012 at 9:01 PM, Arun Muralidharan <> wrote:
> Can you be more specific on how your sending process is overloading your receiving process(P1) by making a "blocking" call ? I didnt quite get it. 
> Why dont you try an async design pattern as shown in 
> http://www.trapexit.org/Building_a_Non-blocking_TCP_server_using_OTP_principles 
> -Arun
> 
> 
> 
> On Mon, Sep 3, 2012 at 12:47 PM, Erik Søe Sørensen <> wrote:
> Have you considered having one process for sending and one for receiving (on the same socket)?
> 
> Den 03/09/2012 06.47 skrev "Satyam Shekhar" <>:
> Hi,
> 
> I know this question has been asked many times. 
> 
> http://erlang.2086793.n4.nabble.com/Non-blocking-sends-in-gen-tcp-td2114537.html
> https://groups.google.com/forum/?fromgroups=#!topic/erlang-programming/4DBmCK4GAK8
> 
> But my concern is slightly different. I have a separate sending/receiving process, P1, for a gen_tcp socket which receives messages it has to send, from process P2. There is no acking between the P1 and P2. Data is buffered at P2 and data acking is client driven, i.e that client says how much data it has received when it reconnects. Right now, P2 sends data to P1 as soon as it generates any data, and also adds it to its buffer, so that it can send it to the client if the socket gets closed before client receives it.
> 
> The issue is, since the gen_tcp send call is blocking, and P2 might flood P1s mailbox at times, received messages(socket in active once mode) from the client are delayed quite a bit.
> 
> What is the best way to handle this?
> 
> Regards,
> Satyam Shekhar
> 
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