5. Tutorials

• 5.1. Overview
  • 5.1.1. Prerequisites
  • 5.1.2. Language Standards we use and which are supported by LN
    • 5.1.2.1. Standards used in this documentation
    • 5.1.2.2. Standards supported by LN
  • 5.1.3. Goals of this Tutorial
  • 5.1.4. Overview / Road Map on the tutorial
• 5.2. Summary of basic Concepts and Features of Links and Nodes
  • 5.2.1. Process Management and Start-Up Dependencies
  • 5.2.2. Isolation from the Environment
  • 5.2.3. Templating for reducing Boiler-Plate
  • 5.2.4. Inter-process Communication via Message-passing
• 5.3. How to use the Links and Nodes Manager (LNM)
  • 5.3.1. Components
    • 5.3.1.1. Instance Name and Port
    • 5.3.1.2. Multi-User / Multi-Instance Capability
  • 5.3.2. Starting LNM with an essential Configuration
  • 5.3.3. Use of Functions and Variables in the LNM Configuration File
  • 5.3.4. Process Management
    • 5.3.4.1. Starting simple Processes
      • 5.3.4.1.1. Process Definitions
      • 5.3.4.1.2. Defining the Node which a Process runs on
      • 5.3.4.1.3. Using the LN Manager GUI
      • 5.3.4.1.4. Exiting the LN Manager GUI
      • 5.3.4.1.5. Processes which terminate without Error
    • 5.3.4.2. Start-up Dependencies
      • 5.3.4.2.1. Process Dependencies
      • 5.3.4.2.2. Grouping Processes
      • 5.3.4.2.3. Different Kinds of Dependencies
      • 5.3.4.2.4. Synchronizing Start-up of several Processes
        • 5.3.4.2.4.1. By Terminal Output: ready-regex
        • 5.3.4.2.4.2. By Time: ready-time
        • 5.3.4.2.4.3. Starting further processes: start-on-ready
    • 5.3.4.3. Starting Processes on other Network Nodes
      • 5.3.4.3.1. Logical Node Names
    • 5.3.4.4. Defining the Process Environment
    • 5.3.4.5. Reloading the Configuration
      • 5.3.4.5.1. Environment Variables defined by the LN Manager
      • 5.3.4.5.2. Changing the Current Work Directory (CWD)
    • 5.3.4.6. Process Priorities and Scheduling Policy
      • 5.3.4.6.1. Setting Process Priorities
      • 5.3.4.6.2. Changing the Scheduling Policy to Real-Time Scheduling
  • 5.3.5. Inter-Process Communication
    • 5.3.5.1. Using Message Passing
      • 5.3.5.1.1. Publish/Subscribe Pattern
      • 5.3.5.1.2. Messages as Data Types
      • 5.3.5.1.3. Topics
      • 5.3.5.1.4. Message Definitions: Defining Messages as Data Types
    • 5.3.5.2. Message Definition Names
    • 5.3.5.3. Topics and Services Names
      • 5.3.5.3.1. Storage of Message Definitions
      • 5.3.5.3.2. Making Message Definitions known to the LN Manager
      • 5.3.5.3.3. Inspecting Topics in the LNM GUI
      • 5.3.5.3.4. Recommendations for managing Message Definitions
    • 5.3.5.4. Introducing Services
      • 5.3.5.4.1. Advantages and Disadvantages
      • 5.3.5.4.2. How to create Service Message Definitions
      • 5.3.5.4.3. Providing and accessing Services
      • 5.3.5.4.4. Inspecting Services in the LNM GUI
    • 5.3.5.5. LN Parameters
  • 5.3.6. Further useful Configuration Options
    • 5.3.6.1. Using Templates in the LNM Configuration
    • 5.3.6.2. Include Directives
    • 5.3.6.3. Conditional Evaluation
    • 5.3.6.4. Including a Set of Files
    • 5.3.6.5. Including generated Files on the fly
• 5.4. Designing a Modularized System by an Example
  • 5.4.1. How to automate an Elevator
  • 5.4.2. Message definitions
    • 5.4.2.1. Message definition for UI service requests
    • 5.4.2.2. Message definition for hardware actors
    • 5.4.2.3. Message definition for hardware sensors
    • 5.4.2.4. Division into processes and modules
• 5.5. Python Tutorial
  • 5.5.1. Setting up the Environment
  • 5.5.2. Writing the LN Manager Configuration
    • 5.5.2.1. Testing the new configuration
  • 5.5.3. Using the Communication Functions in the Client API: A First Overview
  • 5.5.4. Implementing the Elevator Control Processes
    • 5.5.4.1. Communicating with publish/subscribe topic messages
      • 5.5.4.1.1. The Elevator Hardware Simulation
      • 5.5.4.1.2. Publishing and receiving Data in the elevator process
      • 5.5.4.1.3. Publishing the Sensor Data
      • 5.5.4.1.4. Receiving Motor Control Commands as a Subscriber
      • 5.5.4.1.5. Extracting API Constants from the Hardware Simulation
      • 5.5.4.1.6. The Controller Process
      • 5.5.4.1.7. Receiving Sensor Messages
      • 5.5.4.1.8. Using Time-Outs
      • 5.5.4.1.9. Sending Command Messages
    • 5.5.4.2. Connecting UI and Controller with a Service
      • 5.5.4.2.1. Calling the Service from the UI
      • 5.5.4.2.2. The Response Method in the Controller
      • 5.5.4.2.3. Invoking The Service from the UI program
      • 5.5.4.2.4. Implementing the Elevator Control Function
      • 5.5.4.2.5. Error Handling using Exceptions
      • 5.5.4.2.6. Error Handling across Service Messages
      • 5.5.4.2.7. Running the Example
  • 5.5.5. Using the LN Manager GUI to control the Elevator Example
    • 5.5.5.1. Starting all Processes
    • 5.5.5.2. Inspecting the processes
    • 5.5.5.3. Inspecting Topics communication
    • 5.5.5.4. Inspecting Service Calls
    • 5.5.5.5. Reloading the LN Manager Configuration
  • 5.5.6. Detailed Summary on the Python Client API which we have used
    • 5.5.6.1. Client Processes
    • 5.5.6.2. The Python Module
    • 5.5.6.3. LN Client Instance
      • 5.5.6.3.1. Constructor
    • 5.5.6.4. Message Definitions
      • 5.5.6.4.1. Publish/Subscribe Definitions
      • 5.5.6.4.2. Service Message Definitions
    • 5.5.6.5. Port Objects
      • 5.5.6.5.1. Subscriber Ports
      • 5.5.6.5.2. Publisher Ports
    • 5.5.6.6. Port Members
      • 5.5.6.6.1. port.packet
    • 5.5.6.7. Port Methods
      • 5.5.6.7.1. port.write()
      • 5.5.6.7.2. port.read()
    • 5.5.6.8. Service Providers and Service Clients
      • 5.5.6.8.1. Service Provider
        • 5.5.6.8.1.1. Setup
        • 5.5.6.8.1.2. Service Handling
    • 5.5.6.9. Service Clients: Wrapper Class and Service Objects
• 5.6. C++ Tutorial
  • 5.6.1. Setting up the Programming Environment for C++
  • 5.6.2. Writing the LN Manager Configuration
    • 5.6.2.1. Testing the new configuration
  • 5.6.3. Using the Communication Functions in the Client API: A First Overview
    • 5.6.3.1. Code generation step
    • 5.6.3.2. Clients and Topics
    • 5.6.3.3. Topics communication with publish / subscribe
  • 5.6.4. Implementing the Elevator Control Processes
    • 5.6.4.1. Communicating with publish/subscribe topic messages
      • 5.6.4.1.1. The Elevator Hardware Simulation
      • 5.6.4.1.2. Generating the ln_messages.h header
      • 5.6.4.1.3. Publishing and receiving Data in the Elevator Process
      • 5.6.4.1.4. Publishing the Sensor Data
      • 5.6.4.1.5. Receiving Motor Control Commands as a Subscriber
      • 5.6.4.1.6. Using Time-Outs
      • 5.6.4.1.7. The Hardware Control Loop
      • 5.6.4.1.8. Extracting API Constants from the Hardware Simulation
      • 5.6.4.1.9. The Controller Process
      • 5.6.4.1.10. Receiving Sensor Messages
      • 5.6.4.1.11. Sending Command Messages
    • 5.6.4.2. Connecting UI and Controller with a Service
      • 5.6.4.2.1. Implementing Service Calls
      • 5.6.4.2.2. Service Clients
      • 5.6.4.2.3. Service Provider
        • 5.6.4.2.3.1. Initialization
      • 5.6.4.2.4. Calling the Service from the UI
        • 5.6.4.2.4.1. Code generation for the service interface
        • 5.6.4.2.4.2. Client Initialization
        • 5.6.4.2.4.3. Calling the Service from C++
        • 5.6.4.2.4.4. Running the Client
      • 5.6.4.2.5. The Service Handler in the Controller
        • 5.6.4.2.5.1. Initialization and Registration
        • 5.6.4.2.5.2. The Top-Level Call Handler
        • 5.6.4.2.5.3. Running the Handler
        • 5.6.4.2.5.4. Implementing the Elevator Control in the Bottom-Level Handler Method
    • 5.6.4.3. Error Handling using Exceptions
      • 5.6.4.3.1. Adding Exception Handling to the Elevator
      • 5.6.4.3.2. Refactoring the Error Handling
      • 5.6.4.3.3. Error Handling in Service Clients
      • 5.6.4.3.4. Handling of exceptions across languages
  • 5.6.5. Running the Example
  • 5.6.6. Using the LN Manager GUI to control the Elevator Example
    • 5.6.6.1. Starting all Processes
    • 5.6.6.2. Inspecting the processes
    • 5.6.6.3. Inspecting Topics communication
    • 5.6.6.4. Inspecting Service Calls
  • 5.6.7. Swapping C++ Components out for Python Components
    • 5.6.7.1. Reloading the Configuration
  • 5.6.8. Tips for compiling / debugging clients
  • 5.6.9. Summary on the C++ Client API which we have used
    • 5.6.9.1. Message Definitions
      • 5.6.9.1.1. Topic Message Definitions
      • 5.6.9.1.2. Service Message Definitions
    • 5.6.9.2. Code generation
      • 5.6.9.2.1. Using the generated header file
    • 5.6.9.3. Client Processes
    • 5.6.9.4. Using the libln library
      • 5.6.9.4.1. Client Objects
        • 5.6.9.4.1.1. Constructor
      • 5.6.9.4.2. API for Topics communication with publish / subscribe
        • 5.6.9.4.2.1. Port Objects
          • 5.6.9.4.2.1.1. Subscriber Ports
          • 5.6.9.4.2.1.2. Publisher Ports
          • 5.6.9.4.2.1.3. Port Methods
            • 5.6.9.4.2.1.3.1. outport.write()
            • 5.6.9.4.2.1.3.2. inport::read()
      • 5.6.9.4.3. API for using LN Services from C++
        • 5.6.9.4.3.1. Recapitulation of the Tutorial Example
        • 5.6.9.4.3.2. Elements used in the Service Client
          • 5.6.9.4.3.2.1. ln::client::get_service()
          • 5.6.9.4.3.2.2. ln::service::call()
        • 5.6.9.4.3.3. Elements used in the Service Provider
          • 5.6.9.4.3.3.1. Initialization
          • 5.6.9.4.3.3.2. Top-Level Handler
          • 5.6.9.4.3.3.3. Request Handling in the Bottom-Level Handler
          • 5.6.9.4.3.3.4. ln::client::wait_and_handle_service_group_requests(): Running the Service
          • 5.6.9.4.3.3.5. ln::client::handle_service_group_in_thread_pool(): Thread Configuration for the Service