Powershell FileSystemWatcher script firing twice on some new files

Question

I'm using FileSystemWatcher to monitor a folder where documents are scanned to. When a new file is detected, it will send an email to notify someone. It's working as is, but sometimes (not every file) it will trigger 2 or 3 times on a new file and send the email 2-3 times for the same file. I'm guessing it has to do with the way the file is created by the scanner or something like that.

I'm trying to figure out a way to protect against this happening, to ensure it only sends one email per file. Any suggestions would be greatly appreciated.

$PathToMonitor = "\\path\to\folder"

$FileSystemWatcher = New-Object System.IO.FileSystemWatcher
$FileSystemWatcher.Path  = $PathToMonitor
$FileSystemWatcher.Filter  = "*.*"
$FileSystemWatcher.IncludeSubdirectories = $false

$FileSystemWatcher.EnableRaisingEvents = $true

$Action = {
    if ($EventArgs.Name -notlike "*.pdf" -and $EventArgs.Name -notlike "*.tif") {
        return
    }
        $details = $event.SourceEventArgs
        $Name = $details.Name
        $Timestamp = $event.TimeGenerated
        $text = "{0} was submitted on {1}." -f $Name, $Timestamp
        
        $FromAddress = "Email1 <[email protected]>"
        $ToAddress = "Email2 <[email protected]>"
        $Subject = "New File"
        $SMTPserver = "123.4.5.678"
    
        Send-MailMessage -From $FromAddress -To $ToAddress -Subject $Subject -Body $text -SmtpServer $SMTPserver
    
}

$handlers = . {
    Register-ObjectEvent -InputObject $FileSystemWatcher -EventName Created -Action $Action -SourceIdentifier FSCreateConsumer
}

try {
    do {
        Wait-Event -Timeout 5
    } while ($true)
}
finally {
    Unregister-Event -SourceIdentifier FSCreateConsumer
    
    $handlers | Remove-Job
    
    $FileSystemWatcher.EnableRaisingEvents = $false
    $FileSystemWatcher.Dispose()
}

Answer 1

This may be because you listen too many notifications. The default is LastWrite, FileName, and DirectoryName FileName is sufficient for your need and may prevent your issue.

$FileSystemWatcher.NotifyFilter = [System.IO.NotifyFilters]::FileName

As a remark, I don't know why you use Wait-Event -Timeout 5. Script is working fine without the try{} block.

EDIT: Add a ConcurrentDictionary to avoid duplicate events

Try this sample code. I've included only the beginning part of your script. End is untouched.

$PathToMonitor = "\\path\to\folder"
$KeepFiles = 5  #minutes

$MonitoredFiles = New-Object -TypeName 'System.Collections.Concurrent.ConcurrentDictionary[[System.String],[System.DateTime]]'

$FileSystemWatcher = New-Object System.IO.FileSystemWatcher
$FileSystemWatcher.Path  = $PathToMonitor
$FileSystemWatcher.Filter  = "*.*"
$FileSystemWatcher.IncludeSubdirectories = $false
$FileSystemWatcher.NotifyFilter = [System.IO.NotifyFilters]::FileName

$FileSystemWatcher.EnableRaisingEvents = $true


$Action = {
    if ($EventArgs.Name -notlike "*.pdf" -and $EventArgs.Name -notlike "*.tif") {
        return
    }

    #Cleaning events -gt 5mn
    $Now = [System.DateTime]::Now
    $OriginEventDate = [System.DateTime]::MinValue
    foreach($MonitoredFile in [System.Linq.Enumerable]::ToList(($MonitoredFiles.Keys))) {
        if ($MonitoredFiles.TryGetValue($MonitoredFile, [ref]$OriginEventDate)) {
            if ($OriginEventDate.AddMinutes($KeepFiles) -gt $Now) {
                try {
                    [void]$MonitoredFiles.Remove($MonitoredFile)
                } 
                catch {}
            }
        }
    }

    $ProcessEvent = $false
    # any same file creation event within 5mn are discarded
    $OriginEventDate = [System.DateTime]::MinValue
    if ($MonitoredFiles.TryGetValue($event.SourceEventArgs.Name, [ref]$OriginEventDate)) {
        if ($OriginEventDate -ne [System.DateTime]::MinValue -and $OriginEventDate.AddMinutes($KeepFiles) -le $Now) {
            return
        }
        else {
            $ProcessEvent = $true
        }
    }
    else {
        #not successful means a concurrent event was successful, so discard this one.
        if ($MonitoredFiles.TryAdd($event.SourceEventArgs.Name, $event.SourceEventArgs.TimeGenerated)) {
            $ProcessEvent = $true
        }
        else {
            return
        }
    }

    
    if ($ProcessEvent) {
            
        $details = $event.SourceEventArgs
        $Name = $details.Name
        $Timestamp = $event.TimeGenerated
        $text = "{0} was submitted on {1}." -f $Name, $Timestamp
        
        $FromAddress = "Email1 <[email protected]>"
        $ToAddress = "Email2 <[email protected]>"
        $Subject = "New File"
        $SMTPserver = "123.4.5.678"
    
        Send-MailMessage -From $FromAddress -To $ToAddress -Subject $Subject -Body $text -SmtpServer $SMTPserver
    }
}