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5.3. Developing for asynchronous processes.md

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Development for asynchronous processes

Asynchronous Processing

  • Multiple CPU cores enables multiple threads.
  • In past, it was complex with locks, took years to master.
  • Today, it's simplified with ex. TPL (Task Parallel Library).
  • Task Parallel Library (TPL)
    • Extends System.Threading to simplify parallelism and concurrency.
    • Dynamical scaling of degree of concurrency for maximum efficiency.
    • Handles partitioning of work, scheduling threads in thread pool, cancellation, state management and more.
    • A task holds metadata about the delegate: whether delegate has started/completed executing and it's resulting value.
    • Use async-await to refactor TPL code.

Serverless computing

  • Useful for "gluing" together disparate systems (e.g. integration solutions)
  • They can all define input, actions, conditions, and output.
  • You can run each of them on a schedule or via a trigger.

Azure Functions

  • FaaS: Functions as a Service
  • Support many languages such as C#, F#, Node.js, Java or PHP.
  • Excellent for: data processing, integrating systems working with IoT, simple APIs/micro-services.
  • Integrates with Azure and 3rd party services
    • Integrations can trigger your function or serve as input/output.
  • You can edit & compile & test (with request manipulations) & save in Portal.
  • One function app can have many functions.
  • In .NET

    • Provided by Azure WebJobs SDK.

    • json specifies input/outputs.

        {
    "disabled": false,
    "bindings":[ {
        "type": "queueTrigger",
        "direction": "in",
        "name": "message",
        "queueName": "announcementqueue",
        "connection":"StorageConnectionString"
      } ]
  }

    • Required fields: direction, name, type

    • C# script binds to "in" property as a method parameter:

        public static void Run(string message, System.TraceWriter log)
  {
    log.Info($"New message: {message}");
  }

Logic Apps

  • Build & schedule & automate processes as workflows.

  • Scenarios: B2B, on-prem or cloud only or both, data/system integration, enterprise application integration (EAI).

  • You can integrate with on-premises using an On-premises Data Gateway.

    1. Download and install gateway
    2. Create Azure resource for gateway (on-premises data gateway)
    3. Connect to on-premises data
      • Add a connector that supports on-premises connections, for example, SQL Server.
      • Select Connect via on-premises data gateway.

  • Build visually in Logic Apps designer, available in Azure portal & Visual Studio. You can also use PowerShell & ARM templates for select tasks.

  • Describe in a json template:

    {
  "$schema":"https://schema.management.azure.com/schemas/2016-06-01/Microsoft.Logic.json",
  "contentVersion":"1.0.0.0",
  "parameters": {
    "uri": { "type": "string" }
  },
  "triggers": {
    "request": { "type": "request", "kind": "http" }
  },
  "actions": {
    "readData": {
      "type":"Http",
      "inputs": { "method":"GET"," uri":"@parameters('uri')" }
    }
  },
  "outputs": {}
}

Implement interfaces for storage or data access

  • Blocking the calling thread during I/O
    • Thread enters a wait state which other operations can't use it.
    • Anti-pattern as it reduces performance & bad for vertical scalability.
  • Asynchronous code
    • Do not wait for I/O, transition long-running work other CPU cores.
    • Allows servers to handle more requests & UIs to be more responsive.
  • Use asynchronous interfaces for all data tier code, pair those with interfaces with asynchronous versions.
    • E.g. if you have Entity Framework in controller, you'll need to rewrite code if you use another mapper or database in future => Use interfaces with async implementation.