Queue, Entity Queue

Enqueue messages and entities

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  • Library:

  • Simulink / Messages & Events

    SimEvents

  • Queue block

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. The Queue block and the Entity Queue block are the same blocks with different default values for the Overwrite the oldest element if queue is full check box.

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.

Ports

Input

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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

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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

Number of entities that have departed the block.

Dependencies

To enable this port, select Overwrite the oldest element if queue is full check box, and click the Statistics tab and select the box labeled Number of entities departed, d.

Data Types: double

Number of entities that have not yet departed the block.

Dependencies

To enable this port, select Overwrite the oldest element if queue is full check box, and click the Statistics tab and select the box labeled Number of entities in block, n.

Data Types: double

Average wait time for entities in the block.

Dependencies

To enable this port, select Overwrite the oldest element if queue is full check box, and click the Statistics tab and select the box labeled Average wait, w.

Data Types: double

Port_l outputs the average length of the entity queue.

Dependencies

To enable this port, select Overwrite the oldest element if queue is full check box, and click the Statistics tab and select the box labeled Average queue length, l.

Data Types: double

Number of entities that are pulled out of this block.

Dependencies

To enable this port, select Overwrite the oldest element if queue is full check box, and click the Statistics tab and select the box labeled Number of entities extracted, ex.

Data Types: double

Parameters

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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 (SimEvents).

    For an example, see Manage Entities Using Event Actions (SimEvents).

Programmatic Use

Block Parameter: QueueOverwriting
Type: character vector
Values: 'on' | 'off'
Default: 'on' (for Simulink) and 'off' (for SimEvents)

Specify the capacity of the queue.

Programmatic Use

Block Parameter: Capacity
Type: character vector
Values: '25' | scalar
Default: '25'

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 (SimEvents). 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'

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'

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'

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'

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'

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 (SimEvents).

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 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 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'

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 (SimEvents).

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'

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 (SimEvents).

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'

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 (SimEvents).

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'

Model Examples

Animate and Understand Sending and Receiving Messages

Animate and Understand Sending and Receiving Messages

Send, receive, and visualize messages. The example also shows how to use Simulation Data Inspector, Animation, and Storage Inspector to understand how messages flow in your model.

Use a Queue Block to Manage Messages

Use a Queue Block to Manage Messages

Use a Queue block to store and queue messages. The Queue block allows you to specify message storage capacity, overwriting policy, and sorting policy during message transitions.

Establish Message Send and Receive Interfaces Between Software Components

Establish Message Send and Receive Interfaces Between Software Components

Model message-based communication between software components that run in different applications. The example also shows how to prepare model components for C++ code generation.

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

Extended Capabilities

See Also

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Topics

Introduced in R2016a

Simulink Documentation

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