[PowerShell每日技巧]高效运行后台任务(20140414)

DAIC

Using background jobs to run tasks concurrently often is not very efficient as you might have seen in a previous tip. Background job performance worsens with the amount of data that is returned by a background job.

A much more efficient way uses in-process tasks. They run as separate threads inside the very same PowerShell, so there is no need to serialize return values.

Here is a sample that runs two processes in the background, and one in the foreground, using PowerShell threads. To create some really long-running tasks, each task uses Start-Sleep in addition to some other command:

1. $start = Get-Date
   
2. 
   
3. 
   
4. $task1 = { Start-Sleep -Seconds 4; Get-Service }
   
5. $task2 = { Start-Sleep -Seconds 5; Get-Service }
   
6. $task3 = { Start-Sleep -Seconds 3; Get-Service }
   
7. 
   
8. # run 2 in separate threads, 1 in the foreground
   
9. $thread1 = [PowerShell]::Create()
   
10. $job1 = $thread1.AddScript($task1).BeginInvoke()
    
11. 
    
12. $thread2 = [PowerShell]::Create()
    
13. $job2 = $thread2.AddScript($task2).BeginInvoke()
    
14. 
    
15. $result3 = Invoke-Command -ScriptBlock $task3
    
16. 
    
17. do { Start-Sleep -Milliseconds 100 } until ($job1.IsCompleted -and $job2.IsCompleted)
    
18. 
    
19. $result1 = $thread1.EndInvoke($job1)
    
20. $result2 = $thread2.EndInvoke($job2)
    
21. 
    
22. $thread1.Runspace.Close()
    
23. $thread1.Dispose()
    
24. 
    
25. $thread2.Runspace.Close()
    
26. $thread2.Dispose()
    
27. 
    
28. $end = Get-Date
    
29. Write-Host -ForegroundColor Red ($end - $start).TotalSeconds

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Running these three tasks consecutively would take at least 12 seconds for the Start-Sleep statements alone. In reality, the script only takes a bit more than 5 seconds. The result can be found in $result1, $result2, and $result3. In contrast to background jobs, there is almost no time penalty for returning large amounts of data.

http://powershell.com/cs/blogs/tips/archive/2014/04/14/running-background-jobs-efficiently.aspx