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| Coll |
 Posted: Tue Jul 31, 2007 11:11 am |
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Joined: 31 Jul 2007
Posts: 6
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Hi,
New here, don't know if this is the right forum for this question but...
I haven't found any good information on this.
I have a process streaming data constantly using gen_tcp, right now I spawn this process with erlang:spawn(fun server:start/0).
Then it waits for a connection and start streaming when someone connect.
Everything else in the system is OTP with supervisors and gen_servers.
Now, my problem is that I want some way to nicely shut this process down when the systems shuts down or I for some other reason wants to stop streaming, do clean up (closing socket).
It works if the client connected disconnect, but sometimes I want to shut it down nicely even if the client haven't disconnected.
I guess I could use a receive after 0 and see if I get a message to shutdown between every packet I send over TCP, but I would prefer not to, something tells me it's not very nice to poll my messages all the time. Is there any other way? |
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| Mazen |
| Posted: Wed Aug 01, 2007 8:31 am |
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Joined: 20 Jul 2006
Posts: 164
Location: London
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Hi Coll,
Hmmm tricky one... of course the easiest way would be to actually check your message box every time but if you want to overengineer a little this might work.
Assume you have 1 server process working as a process manager for processes that stream data. The process for streaming data does only that, it streams data, the manager process takes care of the post- and/or pre apply.
so... if first process is a gen server... I could think that the following sequence of actions would be taken.
1) call gen server to start a new stream process with a few args
2) gen server process prepares and starts the process and saves the Pid in a list somewhere
3) call gen server to stop the stream process
4) gen server process prepares and then kills the streaming process.
5) gen server process then cleans up after streaming process
As I said... a little overengineered...
Just thought of something else now... don't know how "beautiful" or "ugly" this is... but you could send a message to yourself..
then every loop you patternmatch for either this message or the stop message.
but after all... after 0 seems the easiest way  |
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| francesco |
| Posted: Wed Aug 01, 2007 11:33 am |
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Joined: 07 Jul 2006
Posts: 249
Location: London
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Hi Coll, welcome to trapexit. You've found the right forum.
Quote: I have a process streaming data constantly using gen_tcp, right now I spawn this process with erlang:spawn(fun server:start/0).
You should use spawn_link instead of spawn, ensuring that the process taking care of the streaming is started by a process in your supervision tree. When you shut down the system (or just the application), this process will be terminated together with all other processes linked to it.
Try it out,
Francesco |
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| Coll |
| Posted: Wed Aug 01, 2007 12:11 pm |
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Joined: 31 Jul 2007
Posts: 6
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Thanks for the answers.
But even if I use spawn link wouldn't the socket still be open even if the process streaming (using the socket) is terminated?
I want to close it properly. |
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| francesco |
| Posted: Wed Aug 01, 2007 5:18 pm |
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Joined: 07 Jul 2006
Posts: 249
Location: London
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Sockets use ports. They are made to act as processes not trapping exits. This means they can be linked to, can send and receive messages and react on exit signals. So if your process is linked to it and it terminates, the exit signal will kill the port/socket.
See: http://www.erlang.org/course/advanced.html#ports for more information. I had a look at the gen_tcp module, and it was not well documented. The above is the best I could find. It should take you a few minutes to hack together a test and proove / disproove the above. |
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| Coll |
| Posted: Thu Aug 02, 2007 12:15 pm |
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Joined: 31 Jul 2007
Posts: 6
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| I see, thanks for the replies. |
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| francesco |
| Posted: Mon Aug 06, 2007 7:09 pm |
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Joined: 07 Jul 2006
Posts: 249
Location: London
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| Coll |
| Posted: Tue Aug 07, 2007 10:33 am |
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Joined: 31 Jul 2007
Posts: 6
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| Yes, I saw the link on the first page, haven't had time to read it through properly yet but I glanced at it and it seems good. |
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