Queue

Enqueue messages and entities

• 

Libraries:
Simulink / Messages & Events
SimEvents

Alternative Configurations of Queue Block:
Entity Queue

Description

This block stores entities or messages in a queue, based on the order of arrival or priority. Each element at the head of the queue departs when the downstream block is ready to accept it.

You can specify the capacity of the queue, and the policy when the queue is full. The block supports three different message or queue sorting policies, first-in-first out (FIFO), last-in-first out (LIFO), and priority. The priority queue can be used only when the Overwrite the oldest element if queue is full check box is cleared.

Examples

M/M/1 Queuing System

Model a single-queue single-server system with a single traffic source and an infinite storage capacity. In the notation, the M stands for Markovian; M/M/1 means that the system has a Poisson arrival process, an exponential service time distribution, and one server. Queuing theory provides exact theoretical results for some performance measures of an M/M/1 queuing system and this model makes it easy to compare empirical results with the corresponding theoretical results.

• Open Model

M/D/1 Queuing System

Model a single-queue single-server system that has a Poisson arrival process and a server with constant service time. The queue has an infinite storage capacity. In the notation, the M stands for Markovian; M/D/1 means that the system has a Poisson arrival process, a deterministic service time distribution, and one server.

• Open Model

G/G/1 Queuing System and Little's Law

Model a single-queue single-server system in which the interarrival time and the service time are uniformly distributed with fixed means of 1.1 and 1, respectively. The queue has an infinite storage capacity. In the notation, the G stands for a general distribution with a known mean and variance; G/G/1 means that the system's interarrival and service times are governed by such a general distribution, and that the system has one server. You can change the variances of the uniform distributions. You can use this model to examine Little's law.

• Open Model

Modeling Hybrid Systems - Tank Filling

A hybrid system with both continuous time and discrete event sections. The discrete event part models tanks, represented by entities, which are being queued and need to be filled up. Each tank has a "Capacity" attribute. The continuous time part models the process of filling up a tank, modeled by an Integrator. When a tank is filled to capacity, this event can be detected by a Hit Crossing block, which will generate a message corresponding to this event. The generated message will trigger the server to release the tank.

• Open Model

Model Traffic Intersections as a Queuing Network

Create a SimEvents® model to represent a vehicle traffic network and to investigate mean waiting time of vehicles when the network is in steady-state.

• Open Script

Ports

Input

Port_1 — Input entity or message

scalar | vector | matrix

Input entity or message that carries scalar, bus, or vector data to enter the queue.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | fixed point

Output

Port_1 — Output entity or message

scalar | vector | matrix

Output port that allows entities or messages at the head of the queue to depart when a downstream block is ready to accept them.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | fixed point

Port_d — Number of entities that have departed the block

scalar

Number of entities that have departed the block.

Dependencies

To enable this port, in the Statistics tab, select the Number of entities departed, d check box.

Data Types: double

Port_n — Number of entities that have not yet departed the block

scalar

Number of entities that have not yet departed the block.

Dependencies

To enable this port, in the Statistics tab, select the Number of entities in block, n check box.

Data Types: double

Port_w — Average wait time for entities in the block

scalar

Average wait time for entities in the block.

Dependencies

To enable this port, in the Statistics tab, select the Average wait, w check box.

Data Types: double

Port_l — Average length of the entity queue

scalar

Port_l outputs the average length of the entity queue.

Dependencies

To enable this port, in the Statistics tab, select the Average queue length, l check box.

Data Types: double

Port_ex — Number of entities extracted

scalar

Number of entities that are pulled out of this block.

Dependencies

To enable this port, in the Statistics tab, select the Number of entities extracted, ex check box.

Data Types: double

Parameters

Overwrite the oldest element if queue is full — Specify queue overwriting policy

on (default for Simulink^®) | off (default for SimEvents^®)

Select this check box to choose between two queue overwriting policies.

• If you select the check box, an incoming message overwrites the oldest if the queue is full.

  This mode represents a simple message buffer that you can use to generate asynchronous communication between Simulink components and production code.

• If you clear the check box, the block does not accept new messages if the queue is full.

  In this mode, you can manipulate entity data using event actions and visualize statistics.

  To customize actions when entities or messages enter, exit, or are blocked, enter MATLAB^® code in the Entry action, Exit action, or Blocked action field of the Event actions tab. For more information, see Events and Event Actions.

  For an example, see Manage Entities Using Event Actions.

Programmatic Use

Block Parameter: QueueOverwriting

Type: character vector

Values: 'on' | 'off'

Default: 'on' (for Simulink) and 'off' (for SimEvents)

Capacity — Specify the capacity of the queue

25 (default) | scalar

Specify the capacity of the queue.

Programmatic Use

Block Parameter: Capacity

Type: character vector

Values: '25' | scalar

Default: '25'

Queue type — Choose the queue type

FIFO (default) | LIFO | Priority

Choose the queue type.

• FIFO — first-in-first-out

• LIFO — last-in-first-out

• Priority — store elements in order of priority, see Serve High-Priority Customers by Sorting Entities Based on Priority. Priority can be selected when you clear the Overwrite the oldest element if queue is full check box.

  Note

  Priority queue does not support fixed point data type.

Programmatic Use

Block Parameter: QueueType

Type: character vector

Values: 'FIFO' | 'LIFO' | 'Priority'

Default: 'FIFO'

Multicast tag — Specify the tag when accepting entities broadcast via multicast sources

A (default) | character vector

Specify the tag when accepting entities broadcast via multicast sources. The Entity Multicast block requires SimEvents license.

Dependencies

This parameter is visible when you clear the Overwrite the oldest element if queue is full check box, and set Entity arrival source to Multicast.

Programmatic Use

Block Parameter: MulticastTag

Type: character vector

Values: 'A' | character vector

Default: 'A'

Priority source — Specify which attribute of the entity determines its priority

PriorityAttribute (default) | character vector

Specify which attribute of the entity determines its priority.

Dependencies

This parameter is visible when you clear the Overwrite the oldest element if queue is full check box, and set Queue type to Priority.

Programmatic Use

Block Parameter: PrioritySource

Type: character vector

Values: 'PriorityAttribute' | character vector

Default: 'PriorityAttribute'

Sorting direction — Choose the direction of sorting based on priority

Ascending (default) | Descending

Choose the direction of sorting based on priority.

• Ascending — Elements with smaller priority values appear in front of the queue.

• Descending — Elements with greater priority values appear in front of the queue.

Dependencies

This parameter is visible when you clear the Overwrite the oldest element if queue is full check box, and set Queue type to Priority.

Programmatic Use

Block Parameter: SortingDirection

Type: character vector

Values: 'Ascending' | 'Descending'

Default: 'Ascending'

Entity arrival source — Choose the source of arrival for the entities

Input port (default) | Multicast

Choose the source of arrival for the entities.

• Input port — Input port is source of messages or entities.

• Multicast — Entity Multicast block is source of entities. The Entity Multicast block requires SimEvents license.

Dependencies

This parameter is visible when you clear the Overwrite the oldest element if queue is full check box, and set Queue type to Priority.

Programmatic Use

Block Parameter: EntityArrivalSource

Type: character vector

Values: 'Input port' | 'Multicast'

Default: 'Input port'

Event action — Specify the behavior of the entity in certain events

Entry (default) | Exit | Blocked

Specify the behavior of the entity in certain events. Define the behavior in the Event action parameter. The Entry and the Exit actions are called just after the entity entry and just before entity exit. The Blocked action is called after an entity is blocked. For more information, see Events and Event Actions.

Note

If an event action changes an entity, related block behavior such as resorting a priority queue, and rescheduling of any events, will occur after the event action has fully finished and returned.

Note

Event actions do not support fixed point data type.

Dependencies

Event actions are visible when you clear the Overwrite the oldest element if queue is full check box.

Programmatic Use

Block Parameter: EntryAction, ExitAction, BlockedAction

Type: character vector

Values: MATLAB code

Default: ''

Number of entities departed, d — Outputs the number of entities that have departed the block

off (default) | on

Number of entities that have departed the block.

Dependencies

Number of entities departed, d is visible when you clear the Overwrite the oldest element if queue is full check box.

Programmatic Use

Block Parameter: NumberEntitiesDeparted

Type: character vector

Values: 'on' | 'off'

Default: 'off'

Number of entities in block, n — Outputs the number of entities present in the block, that are yet to depart

off (default) | on

Number of entities present in the block, but which are yet to depart.

Dependencies

Number of entities in block, n is visible when you clear the Overwrite the oldest element if queue is full check box.

Programmatic Use

Block Parameter: NumberEntitiesInBlock

Type: character vector

Values: 'on' | 'off'

Default: 'off'

Average wait, w — Outputs the average wait time

off (default) | on

Sum of the wait times for entities departing the block divided by their total number. Wait time is the duration between the Entity Queue block entry and exit of an entity. For more information, see Interpret SimEvents Models Using Statistical Analysis.

Dependencies

Average wait, w is visible when you clear the Overwrite the oldest element if queue is full check box.

Programmatic Use

Block Parameter: AverageWait

Type: character vector

Values: 'on' | 'off'

Default: 'off'

Average queue length, l — Outputs the average length of the entity queue

off (default) | on

Accumulated time-weighted average queue size. The block computes this value by:

1. Multiplying the size of the queue by its duration to calculate time-weighted queue size

2. Summing up all time-weighted queue sizes and averaging them over total time

For more information, see Interpret SimEvents Models Using Statistical Analysis.

Dependencies

Average queue length, l is visible when you clear the Overwrite the oldest element if queue is full check box.

Programmatic Use

Block Parameter: AverageQueueLength

Type: character vector

Values: 'on' | 'off'

Default: 'off'

Number of entities extracted, ex — Number of entities extracted from this block

off (default) | on

Outputs the number of extracted entities which are pulled out from this block by the Entity Find block. The Entity Find block requires a SimEvents license. If the extracted entity is the first entity in the queue, the next entity is set as the pending entity to leave the block. If an entity attribute defines the priority in a priority queue and it is modified by the Entity Find block, the queue is sorted again. When an entity is extracted, Number of entities departed, d, Number of entities in block, n, Average wait, w, and Average queue length, l statistics are updated accordingly. For more information about finding and extracting entities, see Find and Extract Entities in SimEvents Models.

Dependencies

Number of entities extracted, ex is visible when you clear the Overwrite the oldest element if queue is full check box.

Programmatic Use

Block Parameter: NumEntitiesExtracted

Type: character vector

Values: 'on' | 'off'

Default: 'off'

Block Characteristics

Data Types	Boolean | bus | double | enumerated | fixed point | integer | single | string
Direct Feedthrough	no
Multidimensional Signals	yes
Variable-Size Signals	no
Zero-Crossing Detection	no

Alternative Configurations

Entity Queue — Enqueue messages and entities

The Entity Queue block clears the Overwrite the oldest element if queue is full parameter, sets the Capacity parameter to 25, and sets the Queue type parameter to FIFO.

Libraries:
Simulink / Messages & Events
SimEvents

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Code generation is not supported for event actions and statistics.

When you generate code for a model that contains a message queue and has multitasking enabled, enable concurrent tasking behavior if that model will be deployed to a multitasking environment. Otherwise, the generated code has the potential for data corruption. You enable concurrent tasking behavior by selecting Allow tasks to execute concurrently on target.

Version History

Introduced in R2016a