![]() The current implementation of ForEach-Object -Parallel creates a new runspace for each script block execution instance. So in order to run multiple scripts simultaneously multiple runspaces must be created. Scripts have to run in runspace contexts and only one script thread can run at a time within a runspace. PowerShell itself imposes conditions on how scripts run concurrently, based on its design and history. But that turned out to be a performance bottleneck, and now a dedicated thread is used to add tasks to the pool. Adding tasks to the task pool was initially performed on the ForEach-Object cmdlet piped input processing thread. An Add method allows tasks to be added to the pool, but if it is full then the method blocks until a new slot becomes available. Throttling is accomplished by a PSTaskPool class that holds running tasks (running scripts), and has a settable size limit which is set to the throttle limit value. The primary addition is the ability to limit the number of concurrent scripts running at a given time with the -ThrottleLimit parameter. ![]() Implementation detailsĪs previously mentioned, the new ForEach-Object -Parallel feature uses existing PowerShell functionality to run script blocks concurrently. So, it is important to use this feature wisely. But removing the -Parallel parameter and running the ForEach-Object cmdlet normally, results in completion in about 18 milliseconds. ![]() ![]() Consequently, it takes over 10 seconds to complete. The ThrottleLimit is 5 by default so only 5 runspace/threads are created at a time, but still a runspace and thread is created 1000 times to do a simple string evaluation. The above example, a trivial script block is run 1000 times. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |