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Powershell后臺(tái)作業(yè)、異步操作實(shí)例

更新時(shí)間：2014年04月16日 11:38:48 作者：

如果需要加快執(zhí)行一個(gè)腳本，你可能需要用到后臺(tái)作業(yè)。后臺(tái)作業(yè)能同時(shí)運(yùn)行腳本中多個(gè)事件

Powershell是單線(xiàn)程程序且一次只能做一件事情。后臺(tái)作業(yè)能額外增加Powershell進(jìn)程在后臺(tái)處理作業(yè)。當(dāng)需要程序同時(shí)運(yùn)行且數(shù)據(jù)量不是很大時(shí)它能很好的解決問(wèn)題。但從Powershell后臺(tái)回傳數(shù)據(jù)是一個(gè)非常麻煩的工作，它將浪費(fèi)很多時(shí)間。將會(huì)導(dǎo)致腳本更慢。

這里有3個(gè)并發(fā)執(zhí)行任務(wù)：

復(fù)制代碼代碼如下:

$start = Get-Date

# get all hotfixes
$task1 = { Get-Hotfix }

# get all scripts in your profile
$task2 = { Get-Service | Where-Object Status -eq Running }

# parse log file
$task3 = { Get-Content -Path $env:windir\windowsupdate.log | Where-Object { $_ -like '*successfully installed*' } }

# run 2 tasks in the background, and 1 in the foreground task
$job1 =  Start-Job -ScriptBlock $task1
$job2 =  Start-Job -ScriptBlock $task2
$result3 = Invoke-Command -ScriptBlock $task3

# wait for the remaining tasks to complete (if not done yet)
$null = Wait-Job -Job $job1, $job2

# now they are done, get the results
$result1 = Receive-Job -Job $job1
$result2 = Receive-Job -Job $job2

# discard the jobs
Remove-Job -Job $job1, $job2

$end = Get-Date
Write-Host -ForegroundColor Red ($end - $start).TotalSeconds

上面執(zhí)行全部的任務(wù)消耗了5.9秒。三個(gè)任務(wù)的結(jié)果將分別存入$result1, $result2, 和 $result3.
讓我們?cè)倮^續(xù)查看相繼在前臺(tái)執(zhí)行完命令需要多長(zhǎng)時(shí)間：

復(fù)制代碼代碼如下:

$start = Get-Date

# get all hotfixes
$task1 = { Get-Hotfix }

# get all scripts in your profile
$task2 = { Get-Service | Where-Object Status -eq Running }

# parse log file
$task3 = { Get-Content -Path $env:windir\windowsupdate.log | Where-Object { $_ -like '*successfully installed*' } }

# run them all in the foreground:
$result1 = Invoke-Command -ScriptBlock $task1
$result2 = Invoke-Command -ScriptBlock $task2
$result3 = Invoke-Command -ScriptBlock $task3

$end = Get-Date
Write-Host -ForegroundColor Red ($end - $start).TotalSeconds

結(jié)果，這次只花費(fèi)了5.05秒。與后臺(tái)作業(yè)幾乎同時(shí)完成，所以后臺(tái)作業(yè)更適合解決長(zhǎng)時(shí)間執(zhí)行的任務(wù)。從三個(gè)任務(wù)返回的數(shù)據(jù)觀(guān)察，好處是這種按順數(shù)在前臺(tái)獲得數(shù)據(jù)能減少了執(zhí)行過(guò)程的開(kāi)銷(xiāo)。

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