Use System.Threading.Mutex to make threadsafe

eng/common/scripts/Helpers/PSModule-Helpers.ps1

@@ -65,35 +65,53 @@ function Install-ModuleIfNotInstalled()
 
   if ($modules.Count -eq 0)
   {
-    $repositories = (Get-PSRepository).Where({ $_.SourceLocation -eq $repositoryUrl })
-    if ($repositories.Count -eq 0)
-    {
-      Register-PSRepository -Name $repositoryUrl -SourceLocation $repositoryUrl -InstallationPolicy Trusted
-      $repositories = (Get-PSRepository).Where({ $_.SourceLocation -eq $repositoryUrl })
-      if ($repositories.Count -eq 0) {
-        Write-Error "Failed to registory package repository $repositoryUrl."
-        return
+    # Use double-checked locking to avoid locking when module is already installed
+    $mutex = New-Object System.Threading.Mutex($false, "Install-ModuleIfNotInstalled")
+    $null = $mutex.WaitOne()
+
+    try {
+      # Check installed modules again after acquiring lock
+      $modules = (Get-Module -ListAvailable $moduleName)
+      if ($version -as [Version]) {
+        $modules = $modules.Where({ [Version]$_.Version -ge [Version]$version })
       }
-    }
-    $repository = $repositories[0]
-
-    if ($repository.InstallationPolicy -ne "Trusted") {
-      Set-PSRepository -Name $repository.Name -InstallationPolicy "Trusted"
-    }
 
-    Write-Host "Installing module $moduleName with min version $version from $repositoryUrl"
-    # Install under CurrentUser scope so that the end up under $CurrentUserModulePath for caching
-    Install-Module $moduleName -MinimumVersion $version -Repository $repository.Name -Scope CurrentUser -Force
-
-    # Ensure module installed
-    $modules = (Get-Module -ListAvailable $moduleName)
-    if ($version -as [Version]) {
-      $modules = $modules.Where({ [Version]$_.Version -ge [Version]$version })
+      if ($modules.Count -eq 0)
+      {
+        $repositories = (Get-PSRepository).Where({ $_.SourceLocation -eq $repositoryUrl })
+        if ($repositories.Count -eq 0)
+        {
+          Register-PSRepository -Name $repositoryUrl -SourceLocation $repositoryUrl -InstallationPolicy Trusted
+          $repositories = (Get-PSRepository).Where({ $_.SourceLocation -eq $repositoryUrl })
+          if ($repositories.Count -eq 0) {
+            Write-Error "Failed to register package repository $repositoryUrl."
+            return
+          }
+        }
+        $repository = $repositories[0]
+
+        if ($repository.InstallationPolicy -ne "Trusted") {
+          Set-PSRepository -Name $repository.Name -InstallationPolicy "Trusted"
+        }
+
+        Write-Host "Installing module $moduleName with min version $version from $repositoryUrl"
+        # Install under CurrentUser scope so that the end up under $CurrentUserModulePath for caching
+        Install-Module $moduleName -MinimumVersion $version -Repository $repository.Name -Scope CurrentUser -Force
+
+        # Ensure module installed
+        $modules = (Get-Module -ListAvailable $moduleName)
+        if ($version -as [Version]) {
+          $modules = $modules.Where({ [Version]$_.Version -ge [Version]$version })
+        }
+
+        if ($modules.Count -eq 0) {
+          Write-Error "Failed to install module $moduleName with version $version"
+          return
+        }
+      }
     }
-
-    if ($modules.Count -eq 0) {
-      Write-Error "Failed to install module $moduleName with version $version"
-      return
+    finally {
+      $mutex.ReleaseMutex()
     }
   }