Run multiple prerequisite methods in parallel before continuing

Question

I have an application in which I have multiple slow running prerequisite methods I need to call in order to have the data I need to continue.

To try to speed this up I am doing this:

Dictionary<string, string> processOptions = null;
Dictionary<string, string> businessAreas = null;
Dictionary<string, string> requirementLevels = null;
List<TemplateSection> sections = null;
List<TemplateVersion> versions = null;
var prerequisiteTasks = new List<System.Threading.Tasks.Task>();
prerequisiteTasks.Add(new System.Threading.Tasks.Task(() => sections = GetSectionsInTreeForm(latestVersionGuid)));
prerequisiteTasks.Add(new System.Threading.Tasks.Task(() => versions = GetTemplateVersions(templateId)));
prerequisiteTasks.Add(new System.Threading.Tasks.Task(() => processOptions = GetOptionSetProcessPhaseTypes()));
prerequisiteTasks.Add(new System.Threading.Tasks.Task(() => businessAreas = GetOptionSetBusinessAreaTypes()));
prerequisiteTasks.Add(new System.Threading.Tasks.Task(() => requirementLevels = GetOptionSetRequirementLevelTypes()));
prerequisiteTasks.ForEach(x => x.Start());
System.Threading.Tasks.Task.WaitAll(prerequisiteTasks.ToArray());

Each of the methods above can take anything from 2-5 seconds to complete. Is there a nicer way of doing this, or is this something I shouldent do?

P.S. the code as is works great and decreases the time used by around 30%.

Answer 1

Another option is Parallel.Invoke:

Dictionary<string, string> processOptions = null;
Dictionary<string, string> businessAreas = null;
Dictionary<string, string> requirementLevels = null;
List<TemplateSection> sections = null;
List<TemplateVersion> versions = null;
Parallel.Invoke(() => sections = GetSectionsInTreeForm(latestVersionGuid),
 () => versions = GetTemplateVersions(templateId),
 () => processOptions = GetOptionSetProcessPhaseTypes(),
 () => businessAreas = GetOptionSetBusinessAreaTypes(),
 () => requirementLevels = GetOptionSetRequirementLevelTypes());

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It should be pointed out that these tasks run in threads from the thread pool (in both cases: Task and Parallel.Invoke). That's OK for few tasks with a run time from 2-5 seconds, but for long running tasks it is better to use a Task object with TaskCreationOptions.LongRunning to run the task in it's own thread. Otherwise the threadpool threads will be blocked for other short running tasks.

Tasks provide a more granular control but that is not required in your case so I would prefer the simpler Parallel.Invoke variant.

• JensB: Changed my code to this, looks much cleaner and easier to see what is happening.