Task Registration

How it works

The Invoke-Tasks tool provides two functions:

• Register-Task
• Use-Task

The first on allows you to define a task and the second one basically also allows you to define task code but here the scope is to reuse a predefined task.

Registering a task

Basic usage

At the beginning we have a name and a scriptblock. The name has to be unique. The scriptblock can be any Powershell code. It's advisible to keep such tasks short and understandable. The example is using the script analyzer tool (see https://github.com/PowerShell/PSScriptAnalyzer) to analyze a file. If any record has been found (independent of its severity) then an exception will be thrown which would stop the task processing. It's on you to do the same or - as an example - to continue processing when there are records with severity 'information' only.

Register-Task -Name "Static code analysis" {
    $results = Invoke-ScriptAnalyzer ./Invoke-Tasks.ps1
    $results | Format-Table
    if ($results.Count -gt 0) {
        throw "ScriptAnalyzer has found issues!"
    }
}

You're not allowed to write other code than calling Register-Task (and Use-Task), so the only code can be in those script blocks. This is by intention.

Dependency

Each task can have exactly one idea. Reason for this is that Invoke-Tasks does execute all tasks in a defined order and one task at a time only. You can write a task codeblock that does parallel logic as you like but tasks do not. The next example demonstrates how to use it:

Register-Task -Name "Message1" -DependOn "Message2" {
    Write-Host "hello world 1!"
}

Register-Task -Name "Message2"  {
    Write-Host "hello world 2!"
}

No suprise that second message will be printed before the first message. The Invoke-Tasks does check for cyclic dependencies; if you define that those two task depend on each other the tool will stop with an error before any task has been executed.

Tags

You can specify multiple tags at each task with a comma seperated. When call Invoke-Tags with -Tags the tasks are filtered.

Register-Task -Name "Message1" -Tags first {
    Write-Host "hello world 1!"
}

Register-Task -Name "Message2" -Tags second  {
    Write-Host "hello world 2!"
}

However following important notes:

• if you specify more than one tag in -Tags then a task have to contain all those tags otherwise the task won't be executed
• if a task does match depending on another task the dependency will be executed even its tags do not match.

Skip

You can add -Skip to a task and then it is not execute. However if an executable task depend on such a task that dependency will be executed.

Tasks with dependencies

For each task you can specify exactly one dependency by using the name of the related task. With this you can change the order of the task execution.

Register-Task -Name "First Task" -DependsOn "Second Task" {
    Write-Host "First Task"
}

Register-Task -Name "Second Task" {
    Write-Host "Second Task"
}

In this case the output of the second task appears before the output of the first task.