Scheduling Within a PowerShell Script

This script run's a function at a specific interval throughout the day. The script runs as a continuous task and is a simple scheduling engine.

$start = Get-Date

# Scheduler stuff...
$DoSingleRun = 0            # Ignore scheduling and just run once (useful for debugging main function)
$IntervalMins = 15          # Should fit into an hour exactly
$End = "18:50"              # Time of day that script should cease (should be just after last required run time)
$CheckThrottle = 250        # Idle throttle / time check interval (msec)


# Scheduled and helper functions ================================================================

function Log ($text) {
    $stamp = (Get-Date).ToString("HH:mm:ss.fff")
    Write-Host "$stamp | $text"
}

function Do-Stuff {
    # This is where the business of the script goes
}

function Log-Perf {
    # Keeps track of script resource usage
    Log ("Perf CPU(sec): " + [Math]::Round($proc.cpu, 0) + ", Paged Mem (MB): " + [Math]::Round(($proc.pm/1024), 0) + ", WrkSet Mem (MB): " +  [Math]::Round(($proc.ws/1024), 0))
}

# MAIN SCRIPT ====================================================================================

# Initial prep -----------------------------------------------------------------------------------

if ($DoSingleRun) {
    Start-Transcript -Path check-test.log -Append
} else {
    Rename-Item -Path check.log -NewName check-1.log -Force
    Start-Transcript -Path check.log -Append
}
Log "Started script run at $start" 

# Get process for this script
$proc = [System.Diagnostics.Process]::GetCurrentProcess()

# Check scheduler variables
if ((60 % $IntervalMins) -ne 0) {
    Log "Interval error - $IntervalMins mins doesn't fit into an hour!"
    Exit
}

try {
    $EndTime = Get-Date $End
} catch {
    Log "Invalid end time: $End hrs"
    Log $_.Exception.GetType().FullName
    Log $_.Exception.Message
    Exit
}

# Set dummy last run time (aligned to nice start time), and next run time
$LastRunTime = Get-Date
$offset = ($IntervalMins + ($LastRunTime.Minute % $IntervalMins))
$LastRunTime = $LastRunTime.AddMinutes(-$offset)
$LastRunTime = $LastRunTime.AddSeconds(-$LastRunTime.Second)
$NextRunTime = $LastRunTime.AddMinutes($IntervalMins)

#Write-Host "Offset is       " $offset
Log ("Last runtime is " + $LastRunTime)
Log ("Next runtime is " + $NextRunTime)
Log ("Script cease at " + $EndTime)

# Do any once-off initialisation here, 
#  eg connect to a MySQL database, open an "I'm alive" TCP port, load credentials


# Main loop -------------------------------------------------------------------------------------

if ($DoSingleRun) {
    Log ("Doing single run...")
    Do-Stuff
} else {
    While (1) {
        if ($NextRunTime -lt (Get-Date)) {
            Log-Perf
            Log ("Starting run at " + (Get-Date))
            Do-Stuff
            Log ("Completed run at " + (Get-Date))
            $LastRunTime = $LastRunTime.AddMinutes($IntervalMins)
            $NextRunTime = $LastRunTime.AddMinutes($IntervalMins)
            if ($NextRunTime -lt (Get-Date)) {
                Log "WARNING: Next run is going to be late!"
            }
        }
        if ($EndTime -lt (Get-Date)) {
            Log ("Script ending at " + (Get-Date))
            Break
        }
        Start-Sleep -Milliseconds $CheckThrottle
    }
}

# Do any final once-off completion stuff here
# - EG disconnect from database, send "I'm finished" email

Stop-Transcript