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1.9 KiB
1.9 KiB
Erlang, tcp sockets, and active true
If you don't know erlang then you're missing out. 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.
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
flag. A socket can be set to one of:
{active,false}- All data must be obtained through 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 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>