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"Queue" tag

LabVIEW RT block diagram: for-loop structure enqueues 10 integers, then another for-loop structure dequeues the same elements

Queue
RT code

Use a queue to send messages and data between two or more parallel process loops contained within a VI or other VIs. Queues also serve as the foundation for the "Queued State Machine" design pattern.

Elements entering and leaving a queue

RT programming: Queue-based state machines
RT guide PC guide

Queue-based state machines excel at implementing system control, data measurement and processing, and other tasks to respond to inputs from the surrounding physical system and user interface. Learn about three popular design patterns: queued state machine (QSM), queued message handler (QMH), and event-driven producer-consumer loops.

LabVIEW front panels of the "Home Security System" application: RT target with virtual user interface and PC host remote interface

System controller application example: Home Security System
RT code PC code

Example of a complete RT system controller based on the Queued Message Handler (QMH) design pattern with multiple parallel task loops implementing behaviors with queued state machines (QSMs), various inter-process communication techniques (queues and local variables), and inter-target communication techniques (network-published shared variables (NPSVs) and network streams). The PC host human-machine interface (HMI) can remotely connect to the system through the network, monitor the status of the security system, and control it remotely.

LabVIEW PC block diagram: producer-loop contains event structure and guard clause; consumer-loop contains guard clause and case structure; both loops share the same queue reference

Event-driven producer-consumer state machine
PC code

Create a responsive user interface based on two loops operating in parallel: the "producer" loop event structure responds immediately to user interactions such as button clicks and mouse movements that send commands through a queue to the "consumer" loop which performs the required tasks. Separating the state machine into two loops allows the user interface to remain responsive should a consumer task require an unusual amount of time or must wait for a shared resource to become available.