{"id":56068,"date":"2010-10-07T14:55:00","date_gmt":"2010-10-07T14:55:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/pfxteam\/2010\/10\/07\/creating-pre-completed-tasks\/"},"modified":"2010-10-07T14:55:00","modified_gmt":"2010-10-07T14:55:00","slug":"creating-pre-completed-tasks","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/dotnet\/creating-pre-completed-tasks\/","title":{"rendered":"Creating pre-completed Tasks"},"content":{"rendered":"

 <\/p>\n

We’ve been considering adding support for creating completed\nTasks from an existing result.  Here’s a\nprototypical example of where this could be valuable.<\/p>\n

 <\/p>\n

void\nTask<float> ComputeAsync(…)
\n{
\n    if (!resultIsCached)
\n    {
\n        return\nTask<float>.Factory.StartNew(() => Compute());
\n    }
\n    else
\n    {
\n        \/\/ return a Task<float> with\nthe cached result
\n    }
\n}<\/span><\/p>\n


<\/span><\/p>\n

The method usually returns a Task<float> that\nrepresents some compute-intensive operation that will be done asynchronously.  However, the greater code has the ability to\ncache results from previous operations, so there’s a chance that the requested\nresult is already available.  If that’s\nthe case, we just want to return a completed Task with the cached result.  Note that this can be done in .NET 4 as\nfollows:<\/p>\n

 <\/p>\n

TaskCompletionSource<float>\ntcs = new TaskCompletionSource<float>();
\ntcs.SetResult(cachedResult);
\nreturn tcs.Task;<\/span><\/p>\n


<\/span><\/p>\n

But we could make this easier and slightly\nbetter-performing:<\/p>\n

 <\/p>\n

return Task.FromResult(cachedResult);<\/span><\/p>\n


<\/span><\/p>\n

So your input would help. \nIf you’ve got a minute, feel free to answer the following questions\nand\/or provide any other thoughts you have:<\/p>\n

    \n
  1. Would the convenience make this feature worthwhile?<\/li>\n
  2. If you have code that resembles this example, is performance a huge concern (to the point that shaving a few allocations and interlocked operations off of the creation of a pre-completed Task would help)?<\/li>\n
  3. What about support for creating other pre-completed Tasks, e.g. creating a pre-canceled Task or one from an existing Exception?  Details regarding the scenario would help here.<\/li>\n<\/ol>\n

    Thanks!<\/p>\n

     <\/p><\/p>\n","protected":false},"excerpt":{"rendered":"

      We’ve been considering adding support for creating completed Tasks from an existing result.  Here’s a prototypical example of where this could be valuable.   void Task<float> ComputeAsync(…) {     if (!resultIsCached)     {         return Task<float>.Factory.StartNew(() => Compute());     }     else     {         \/\/ return a Task<float> with the cached result     […]<\/p>\n","protected":false},"author":485,"featured_media":58792,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[7908],"tags":[7907,7921,7927,7912],"class_list":["post-56068","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-pfxteam","tag-net-4","tag-feedback-requested","tag-new-feature","tag-task-parallel-library"],"acf":[],"blog_post_summary":"

      We’ve been considering adding support for creating completed Tasks from an existing result.  Here’s a prototypical example of where this could be valuable.   void Task<float> ComputeAsync(…) {     if (!resultIsCached)     {         return Task<float>.Factory.StartNew(() => Compute());     }     else     {         \/\/ return a Task<float> with the cached result     […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/posts\/56068","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/users\/485"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/comments?post=56068"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/posts\/56068\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/media\/58792"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/media?parent=56068"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/categories?post=56068"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/tags?post=56068"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}