PowerShell File Monitoring and Text-to-Speech - powershell

Question

I am new to PowerShell and I'm trying to help a friend write a script that will constantly monitor a file and whenever the file changes, the new text in the file is read aloud (the text file is constantly edited and all of the old content within it is replaced by new content which is taken from emails as they arrive).
The script works perfectly as far as pulling the content from the file and reading it aloud, but I'm having one small issue in that it reads the contents either two or four times, while I only need it to read it once.
Additionally, while PowerShell is speaking the content, it doesn't update/queue changes in the file, so if two changes are made while PowerShell is speaking a prior change, the first change is skipped over and only the most recent change is read aloud. Is there a way to make it queue all changes of the file and read them sequentially?
What I currently have is
Add-Type -AssemblyName System.speech
$speak = New-Object System.Speech.Synthesis.SpeechSynthesizer
$speak.Rate = 0 # -10 is slowest, 10 is fastest
$watcher = New-Object System.IO.FileSystemWatcher
$watcher.Path = "C:\Users\Dylan\Desktop\"
$watcher.Filter = "alarm.txt"
$watcher.IncludeSubdirectories = $false
$watcher.EnableRaisingEvents = $true
$AlarmLocation = "C:\Users\Dylan\Desktop\alarm.txt"
$changeAction = {
$Alarm = (Get-Content $AlarmLocation)
$speak.Speak($Alarm)
}
Register-ObjectEvent $watcher "Changed" -Action $changeAction
while ($true) {sleep 5}
Am I missing something obvious here or is there a different function I have to include?
Thank you

Answer 1

The issue with multiple events is explained here:
https://blogs.msdn.microsoft.com/oldnewthing/20140507-00/?p=1053/
One way to deal with it is to keep track of LastWriteTime.
We can run the speaker in a different thread, so it doesn't block the watcher. That way we will detect if the file changes while speaking.
Something like this...
# When the file is changed,
# the content is stored in the queue,
# and the speaker is signaled.
# it breaks, if the file changes very rapidly.
# use a hashtable for all the vars
# for easier transport across scopes
$vars = [hashtable]::Synchronized(#{})
$vars.speakQueue = New-Object System.Collections.Queue
$vars.speakEvent = New-Object System.Threading.AutoResetEvent $false
$vars.speakLastWriteTime = [DateTime]::MinValue
$vars.speakRunning = $true
$vars.speakPS = [System.Management.Automation.PowerShell]::Create().AddScript({
# this is the speaker thread
Param (
$vars
)
Add-Type -AssemblyName System.speech
$speak = New-Object System.Speech.Synthesis.SpeechSynthesizer
$speak.Rate = 0 # -10 is slowest, 10 is fastest
# run until other thread sets running=false
while($vars.speakRunning) {
# other thread sets the event when content is available
if($vars.speakEvent.WaitOne(100)) {
# use System.Threading.Monitor to make queue thread safe
[System.Threading.Monitor]::Enter($vars.SyncRoot)
try {
# get all alarms
$alarm = while($vars.speakQueue.Count){ $vars.speakQueue.Dequeue() }
}
catch {
}
[System.Threading.Monitor]::Exit($vars.SyncRoot)
# speak now
$alarm | ForEach-Object { $speak.Speak($_) }
}
}
}).AddArgument($vars)
# start new thread
$vars.speakPSHandle = $vars.speakPS.BeginInvoke()
$watcher = New-Object System.IO.FileSystemWatcher
$watcher.Path = "C:\Users\Dylan\Desktop\"
$watcher.Filter = "alarm.txt"
$watcher.IncludeSubdirectories = $false
$watcher.EnableRaisingEvents = $true
$watcher.NotifyFilter = [System.IO.NotifyFilters]::LastWrite
$changeAction = {
$vars = $event.MessageData
# FullPath is the path of the changed file
$item = Get-Item $event.SourceEventArgs.FullPath
# only proceed, if LastWriteTime has changed
if($item.LastWriteTime -ne $vars.speakLastWriteTime) {
$vars.speakLastWriteTime = $item.LastWriteTime
$alarm = Get-Content $event.SourceEventArgs.FullPath -Raw
[System.Threading.Monitor]::Enter($vars.SyncRoot)
try {
# put content in queue
$vars.speakQueue.Enqueue($alarm)
}
catch {
}
[System.Threading.Monitor]::Exit($vars.SyncRoot)
# signal speaker in other thread
$vars.speakEvent.Set()
}
}
$job = Register-ObjectEvent $watcher "changed" -Action $changeAction -SourceIdentifier "FileChanged" -MessageData $vars
while($true) {
Start-Sleep -Milliseconds 25
}
# clean-up, if ever needed...
Unregister-Event "FileChanged"
$vars.speakRunning = $false # leaves while-loop in thread
$vars.speakPS.EndInvoke($vars.speakPSHandle) # waits for thread to end