Task Run with Parameter s

Question

I m working on a multi-tasking network project and I m new on Threading Tasks  I implemented a simple Task Factory StartNew   and I wonder how can I do it with Task Run     Here is the basic code   Task Factory StartNew new Action lt object gt    x    gt           Do something with  x      rawData     I looked into System Threading Tasks Task in Object Browser and I couldn t find a Action lt T gt  like parameter  There is only Action that takes void parameter and no type   There are only 2 things similiar  static Task Run Action action  and static Task Run Func lt Task gt  function  but can t post parameter s  with both   Yes  I know I can create a simple extension method for it but my main question is can we write it on single line with Task Run

User · Answer

I know this is an old thread  but I wanted to share a solution I ended up having to use since the accepted post still has an issue   The Issue   As pointed out by Alexandre Severino  if param  in the function below  changes shortly after the function call  you might get some unexpected behavior in MethodWithParameter   Task Run      gt  MethodWithParameter param       My Solution   To account for this  I ended up writing something more like the following line of code    new Func lt T  Task gt  async  p    gt  await Task Run      gt  MethodWithParam p     Invoke param     This allowed me to safely use the parameter asynchronously despite the fact that the parameter changed very quickly after starting the task  which caused issues with the posted solution    Using this approach  param  value type  gets its value passed in  so even if the async method runs after param changes  p will have whatever value param had when this line of code ran

User · Answer

Idea is to avoid using a Signal like above  Pumping int values into a struct prevents those values from changing  in the struct   I had the following Problem  loop var i would change before DoSomething i  was called  i was incremented at end of loop before      DoSomething i ii  was called   With the structs it doesn t happen anymore  Nasty bug to find  DoSomething i  ii  looks great  but never sure if it gets called each time with a different value for i  or just a 100 times with i 100   hence -  struct  struct Job   public int P1  public int P2        for  int i   0  i  lt  100  i          var job   new Job   P1   i  P2   i   i      structs immutable        Task Run      gt  DoSomething job

User · Answer

private void RunAsync         string param    Hi       Task Run      gt  MethodWithParameter param       private void MethodWithParameter string param          Do stuff     Edit  Due to popular demand I must note that the Task launched will run in parallel with the calling thread   Assuming the default TaskScheduler this will use the  NET ThreadPool   Anyways  this means you need to account for whatever parameter s  being passed to the Task as potentially being accessed by multiple threads at once  making them shared state   This includes accessing them on the calling thread   In my above code that case is made entirely moot   Strings are immutable   That s why I used them as an example   But say you re not using a String     One solution is to use async and await   This  by default  will capture the SynchronizationContext of the calling thread and will create a continuation for the rest of the method after the call to await and attach it to the created Task   If this method is running on the WinForms GUI thread it will be of type WindowsFormsSynchronizationContext   The continuation will run after being posted back to the captured SynchronizationContext - again only by default   So you ll be back on the thread you started with after the await call   You can change this in a variety of ways  notably using ConfigureAwait   In short  the rest of that method will not continue until after the Task has completed on another thread   But the calling thread will continue to run in parallel  just not the rest of the method   This waiting to complete running the rest of the method may or may not be desirable   If nothing in that method later accesses the parameters passed to the Task you may not want to use await at all   Or maybe you use those parameters much later on in the method   No reason to await immediately as you could continue safely doing work   Remember  you can store the Task returned in a variable and await on it later - even in the same method   For instance  once you need to access the passed parameters safely after doing a bunch some other work   Again  you do not need to await on the Task right when you run it   Anyways  a simple way to make this thread-safe with respect to the parameters passed to Task Run is to do this   You must first decorate RunAsync with async   private async void RunAsync     Important Note  Preferably the method marked async should not return void  as the linked documentation mentions   The common exception to this is event handlers such as button clicks and such   They must return void   Otherwise I always try to return a Task or Task lt TResult gt  when using async   It s good practice for a quite a few reasons   Now you can await running the Task like below   You cannot use await without async   await Task Run      gt  MethodWithParameter param      Code here and below in the same method will not run until AFTER the above task has completed in one fashion or another   So  in general  if you await the task you can avoid treating passed in parameters as a potentially shared resource with all the pitfalls of modifying something from multiple threads at once   Also  beware of closures   I won t cover those in depth but the linked article does a great job of it   Side Note  A bit off topic  but be careful using any type of  blocking  on the WinForms GUI thread due to it being marked with  STAThread    Using await won t block at all  but I do sometimes see it used in conjunction with some sort of blocking    Block  is in quotes because you technically cannot block the WinForms GUI thread   Yes  if you use lock on the WinForms GUI thread it will still pump messages  despite you thinking it s  blocked    It s not   This can cause bizarre issues in very rare cases   One of the reasons you never want to use a lock when painting  for example   But that s a fringe and complex case  however I ve seen it cause crazy issues   So I noted it for completeness sake

User · Answer

Use variable capture to  pass in  parameters   var x   rawData  Task Run      gt           Do something with  x        You also could use rawData directly but you must be careful  if you change the value of rawData outside of a task  for example a iterator in a for loop  it will also change the value inside of the task

User · Answer

From now you can also    Action lt int gt  action    o    gt  Thread Sleep o   int param   10  await new TaskFactory   StartNew action  param

User · Answer

Just use Task Run  var task   Task Run      gt          this will already share scope with rawData  no need to use a placeholder       Or  if you would like to use it in a method and await the task later  public Task lt T gt  SomethingAsync lt T gt          var task   Task Run      gt                  presumably do something which takes a few ms here           this will share scope with any passed parameters in the method         return default T                return task

User · Answer

It s unclear if the original problem was the same problem I had  wanting to max CPU threads on computation inside a loop while preserving the iterator s value and keeping inline to avoid passing a ton of variables to a worker function   for  int i   0  i  lt  300  i          Task Run      gt            var x   ComputeStuff datavector  i      value of i was incorrect         var y   ComputeMoreStuff x                              I got this to work by changing the outer iterator and localizing its value with a gate   for  int ii   0  ii  lt  300  ii          System Threading CountdownEvent handoff   new System Threading CountdownEvent 1       Task Run      gt            int i   ii          handoff Signal             var x   ComputeStuff datavector  i           var y   ComputeMoreStuff x                               handoff Wait

[c#] Task.Run with Parameter(s)?

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