Erlang and OTP in Action.pdf - Synrc

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name off the command line starting at annotation #1. It also instantiates the
SimpleCacheHBaseMain class and calls the process method. The process method itself is
where the magic lies and it is illustrated in code listing 13.4.
13.4 The Process Method
while (true) {
try {
OtpErlangObject o = _mbox.receive();
assert (o instanceof OtpErlangTuple); #1
OtpErlangTuple msg = (OtpErlangTuple) o; #2
OtpErlangPid from = (OtpErlangPid) msg.elementAt(0);
OtpErlangRef ref (OtpErlangRef) msg.elementAt(1);
String action = ((OtpErlangAtom) msg.elementAt(2)).toString();
String key = ((OtpErlangList) msg.elementAt(3)).toString();
HBaseTask task = null;
if (msg.arity() == 3) { #3
data = ((OtpErlangBinary) msg.elementAt(3)).binaryValue();
task = new HBaseTask(_mbox, _conn, from, action, key, data);
} else if (msg.arity() == 2) { #4
task = new HBaseTask(_mbox, _conn, from, action, key, null);
} else { #5
OtpErlangTuple res = new OtpErlangTuple(new OtpErlangObject[] {
new OtpErlangAtom("error"),
new OtpErlangAtom("invalid_request") });
}
_mbox.send(from, res);
return;
_exe.submit(task); #6
} catch (Exception e) {
System.out.println("" + e);
}
}
}
We start out in the same way as we did in our example code for our greeting server by
setting up an endless loop. This endless loop is just where we sit in a loop on the message
receive and wait for incoming messages the same way as is done in Erlang/OTP servers.
When we get a message into the mailbox we pull it off the queue and process it. First we
make sure that the message we receive is a tuple with an assertion at code annotation #1.
For right now, if the incoming message is not a tuple we really don’t handle that other than
by printing an exception to stdout. Without a properly formed tuple we don’t know who the
sender is and so cannot even provide a reply if we wanted to. As this code moves further
forward in its readiness for production we will at least want to log out the fact that we got a
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