Message Queue

This document introduces a set of functions about message queue. Message queue is only working in 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 message is a queue message, only one coroutine can get this message. If is topic message, every subscribed coroutine can receive this message.

Import

mq = Import('mq');

subscribe

Subscribe a topic message.

mq.subscribe(qname);

Input:

• qname - a string queue name.

Return value:

• Always return nil.

Error:

• Invalid argument will throw an error.

unsubscribe

Unsubscribe a topic.

mq.unsubscribe(qname);

Input:

• qname - a string queue name.

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 string queue name.
• 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 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 string queue name.
• timeout - a positive integer or nil. If is positive integer, program will wait for timeout microseconds. If omitted or nil, prigram will wait until got a message.

Return value:

• A message.

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