PowerShell Multithreading
本文介绍 PowerShell 中多线程相关内容。
Runspace
在 PowerShell 中，Runspace 是一个独立的执行环境，每个 Runspace 都有自己的变量、函数和状态，互相独立，各 Runspace 之间可以独立的运行 PowerShell 代码，相当于一个独立的会话或线程，允许在同一个进程中并行地运行多个 PowerShell 命令或脚本。
示例代码
该示例代码 multithreading.ps1 模拟了5个线程同时进行某种耗时操作，可以通过打印的时间确认5个线程在并行运行。
# 最大线程数量
$MaxThreadNo = 5
# ShareContext 用于各线程间共享数据
$ShareContext = [Hashtable]::Synchronized(@{ })
$ScriptBlock = {
param (
[Parameter(ValueFromRemainingArguments = $true)]
[string]$ThreadNo
)
$TID = [System.Threading.Thread]::CurrentThread.ManagedThreadId
$TS1 = Get-Date
Write-Host "$(Get-Date -Date $TS1 -Format 'yyyy-MM-dd HH:mm:ss') $TID - thread No: $ThreadNo running"
$Sec = Get-Random -Minimum 5 -Maximum 10
Start-Sleep -Seconds $Sec
$ShareContext[$TID] = "$TID do something took $Sec seconds"
$TS2 = Get-Date
Write-Host "$(Get-Date -Date $TS2 -Format 'yyyy-MM-dd HH:mm:ss') $TID - thread No: $ThreadNo finish, took $(($TS2 - $TS1).TotalSeconds) seconds"
}
# 创建 InitialSessionState 对象，用于初始化 runspace 执行环境
$InitialSessionState = [InitialSessionState]::CreateDefault()
$VariableEntry = New-Object System.Management.Automation.Runspaces.SessionStateVariableEntry -ArgumentList @("ShareContext", $ShareContext, "A thread safe shared context across runspaces")
$initialSessionState.Variables.Add($VariableEntry)
# 创建 Runspace Pool
$RunspacePool = [RunspaceFactory]::CreateRunspacePool(1, $MaxThreadNo, $InitialSessionState, $Host)
$RunspacePool.Open()
$TS1 = Get-Date
# 准备 Runspaces
$Threads = @()
for ($i = 0; $i -lt $MaxThreadNo; $i++) {
$ps = [powershell]::Create().AddScript($ScriptBlock).AddParameter("ThreadNo", $i)
$ps.RunspacePool = $RunspacePool
$status = $ps.BeginInvoke()
$Threads += [PSCustomObject]@{ Powershell = $ps; Status = $status }
}
# 等待所有 Runspace 完成
foreach ($t in $Threads) {
$t.Powershell.EndInvoke($t.Status)
$t.Powershell.Dispose()
}
$TS2 = Get-Date
$TID = [System.Threading.Thread]::CurrentThread.ManagedThreadId
Write-Host "$(Get-Date -Date $TS2 -Format 'yyyy-MM-dd HH:mm:ss') $TID - wait thread finish took $(($TS2 - $TS1).TotalSeconds) seconds"
# 关闭 Runspace Pool
$RunspacePool.Close()
$RunspacePool.Dispose()
# 输出 ShareContext 的内容
Write-Host "---------- Share Context ----------"
foreach ($i in $ShareContext.GetEnumerator() )
{
Write-Host "$($i.Name) : $($i.Value)"
}
在使用多线程时需要注意：
- 示例中的
$InitialSessionState用于初始化$RunspacePool的执行环境，多个Powershell实例使用同一个RunspacePool， 用于在多线程间共享上下文，如果不需要共享上下文，这两个变量是非必须。 - PowerShell 中的 Class 默认情况与申明该 Class 的 Runspace 间具备亲和性(affinity)。类上的方法调用会被编组回创建它的运行空间执行，
这可能会破坏 Runspace 的状态或导致死锁。如果需要在 Runspace 中使用到 Class，在 PowerShell 5.x 中，
可以在执行任务的每个 Runspace 中单独申明 Class，在 PowerShell 7.x 中，可以在定义类时添加
NoRunspaceAffinity属性以避免亲和性问题。 更多请参考 NoRunspaceAffinity attribute - 如在线程中遇到
Write-Host命令输出内容在终端无显示时，可以尝试将主线程的$Host变量注入子线程中，假设注入后名称为$OuterHost， 在子线程中可以使用$OuterHost.UI.WriteLine("Hello")方法进行输出打印。
执行示例代码：
PS C:\Users\admin\Desktop\code\multithreading> powershell.exe -ExecutionPolicy Bypass -File .\multithreading.ps1
2024-07-16 23:29:55 17 - thread No: 2 running
2024-07-16 23:29:55 15 - thread No: 0 running
2024-07-16 23:29:55 16 - thread No: 1 running
2024-07-16 23:29:55 19 - thread No: 3 running
2024-07-16 23:29:55 20 - thread No: 4 running
2024-07-16 23:30:00 16 - thread No: 1 finish, took 5.0827461 seconds
2024-07-16 23:30:00 20 - thread No: 4 finish, took 5.0181769 seconds
2024-07-16 23:30:01 19 - thread No: 3 finish, took 6.0531642 seconds
2024-07-16 23:30:03 15 - thread No: 0 finish, took 8.0786149 seconds
2024-07-16 23:30:04 17 - thread No: 2 finish, took 9.0707772 seconds
2024-07-16 23:30:04 7 - wait thread finish took 9.1223416 seconds
---------- Share Context ----------
20 : 20 do something took 5 seconds
19 : 19 do something took 6 seconds
17 : 17 do something took 9 seconds
16 : 16 do something took 5 seconds
15 : 15 do something took 8 seconds
PS C:\Users\admin\Desktop\code\multithreading>