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diff --git a/erlang-tcp-socket-pull-pattern.md b/erlang-tcp-socket-pull-pattern.md new file mode 100644 index 0000000..c17a799 --- /dev/null +++ b/erlang-tcp-socket-pull-pattern.md @@ -0,0 +1,33 @@ +# Erlang, tcp sockets, and active true + +If you don't know erlang then [you're missing out](http://learnyousomeerlang.com/content). +If you do know erlang, you've probably at some point done something with tcp sockets. Erlang's +highly concurrent model of execution lends itself well to server programs where a high number +of active connections is desired. Each thread can autonomously handle its single client, +greatly simplifying the logic of the whole application while still retaining +[great performance characteristics](http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-1). + +# Background + +For an erlang thread which owns a single socket there are three different ways to receive data +off of that socket. These all revolve around the `active` [setopts](http://www.erlang.org/doc/man/inet.html#setopts-2) +flag. A socket can be set to one of: + +* `{active,false}` - All data must be obtained through [recv/2](http://www.erlang.org/doc/man/gen_tcp.html#recv-2) + calls. This amounts to syncronous socket reading. +* `{active,true}` - All data on the socket gets sent to the controlling thread as a normal erlang + message. It is the thread's responsibility to keep up with the buffered data + in the message queue. This amounts to asyncronous socket reading. +* `{active,once}` - When set the socket is placed in `{active,true}` for a single packet. That + is, once set the thread can expect a single message to be sent to when data + comes in. To receive any more data off of the socket the socket must either + be read from using [recv/2](http://www.erlang.org/doc/man/gen_tcp.html#recv-2) + or be put in `{active,once}` or `{active,true}`. + +# Which to use? + +<Explanation of how other sources claim you should use active,once, and why> + +# Why not to use it + + |