# &adminguide;

## Overview

The mqueue module offers a generic message queue system in shared memory for inter-process communication using the config file. One example of usage is to send time consuming operations to one or several timer processes that consumes items in the queue, without affecting SIP message handling in the socket-listening process.

There can be many defined queues. Access to queued values is done via pseudo variables.

## Dependencies

### &kamailio; Modules

The following modules must be loaded before this module:

- None.

### External Libraries or Applications

The following libraries or applications must be installed before running &kamailio; with this module loaded:

- None.

## Parameters

### `mqueue` (string)

Definition of a memory queue

Default value is none.

Value must be a list of parameters: attr=value;... The attribute 'name' is mandatory, defining the name of the queue. Optional attribute 'size' specifies the maximum number of items in queue, if it is execeeded the oldest one is removed.

The parameter can be set many times, each holding the definition of one queue.

#### Set `mqueue` parameter

    ...
    modparam("mqueue", "mqueue", "name=myq;size=20;")
    modparam("mqueue", "mqueue", "name=qaz")
    ...

## Functions

### `mq_add(queue, key, value)`

Add a new item (key, value) in the queue. If max size of queue is exceeded, the oldest one is removed.

#### `mq_add` usage

    ...
    mq_add("myq", "$rU", "call from $fU");
    ...

### `mq_fetch(queue)`

Take oldest item from queue and fill $mqk(queue) and $mqv(queue) pseudo variables.

Return: true on success (1); false on failure (-1) or no item fetched (-2).

#### `mq_fetch` usage

    ...
    while(mq_fetch("myq"))
    {
       xlog("$mqk(myq) - $mqv(myq)\n");
    }
    ...

### `mq_pv_free(queue)`

Free the item fetched in pseudo-variables. It is optional, a new fetch frees the previous values.

#### `mq_pv_free` usage

    ...
    mq_pv_free("myq");
    ...

### `mq_size(queue)`

Returns the current number of elements in the mqueue.

#### `mq_size` usage

    ...
    $var(q_size) = mq_size("queue");
    xlog("L_INFO", "Size of queue is: $var(q_size)\n");
    ...