Message Queue

This document introduces a set of functions about message queue. Message queue is only working on a coroutine group in the same thread.

There are two kinds of message: queue message and topic message.

Melang supports many coroutines to listen the same queue. If a message is a queue message, only one coroutine can obtain this message. If it is a topic message, every subscribed coroutine can obtain this message.

Import

mq = Import('mq');

subscribe

Subscribe a topic message.

mq.subscribe(qname);

Input:

• qname - a queue name string.

Return value:

• Always return nil.

Error:

• Invalid argument will throw an error.

unsubscribe

Unsubscribe a topic.

mq.unsubscribe(qname);

Input:

• qname - a queue name string.

Return value:

• Always nil.

Error:

• Invalid argument will throw an error.

send

Send message to a specified queue.

mq.send(qname, msg, asTopic);

Input:

• qname - a queue name string.
• msg - the message that we want to send. The type of this argument must be integer, boolean, real or string.
• asTopic - if want to send a queue message, this argument must be false, otherwise true. This is an optional argument. Omitted means false.

Return value:

• Always nil.

Error:

• Invalid argument will throw an error.

recv

mq.recv(qname, timeout);

Input:

• qname - a queue name string.
• timeout - a positive integer or nil. If it is a positive integer, program will wait for timeout microseconds. If it is zero, function returned immediately with nil as the return value. If it is omitted or a nil, prigram will wait until got a message.

Return value:

• A message.
• nil on timeout
• false on failure

Error:

• Invalid argument will throw an error.

Example

//file a.mln
mq = Import('mq');

mq.send('test', 'hello');

//b.mln
mq = Import('mq');
sys = Import('sys');

msg = mq.recv('test');
sys.print(msg);

$ melang a.mln b.mln

The output is:

hello