Is Task Result the same as GetAwaiter GetResult

Question

I was recently reading some code that uses a lot of async methods  but then sometimes needs to execute them synchronously  The code does   Foo foo   GetFooAsync      GetAwaiter   GetResult      Is this the same as  Foo foo   GetFooAsync      Result

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As already mentioned if you can use await  If you need to run the code synchronously like you mention  GetAwaiter   GetResult     Result or  Wait   is a risk for deadlocks as many have said in comments answers  Since most of us like oneliners you can use these for  Net 4 5 lt  Acquiring a value via an async method  var result   Task Run      gt  asyncGetValue    Result   Syncronously calling an async method Task Run      gt  asyncMethod    Wait     No deadlock issues will occur due to the use of Task Run  Source  https   stackoverflow com a 32429753 3850405 Update  Could cause a deadlock if the calling thread is from the threadpool  The following happens  A new task is queued to the end of the queue  and the threadpool thread which would eventually execute the Task is blocked until the Task is executed  Source  https   medium com rubrikkgroup understanding-async-avoiding-deadlocks-e41f8f2c6f5d

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Another difference is when async function returns just Task instead of Task lt T gt  then you cannot use  GetFooAsync      Result    Whereas   GetFooAsync      GetAwaiter   GetResult      still works   I know the example code in the question is for the case Task lt T gt   however the question is asked generally

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I checked the source code of TaskOfResult cs  Source code of TaskOfResult cs   If Task is not completed  Task Result will call Task Wait   method in getter  public TResult Result       get                  If the result has not been calculated yet  wait for it          if   IsCompleted                           We call NOCTD for two reasons                     1  If the task runs on another thread  then we definitely need to notify that thread-slipping is required                    2  If the task runs inline but takes some time to complete  it will suffer ThreadAbort with possible state corruption                         - it is best to prevent this unless the user explicitly asks to view the value with thread-slipping enabled                 if  PFX LEGACY 3 5                                   Debugger NotifyOfCrossThreadDependency                     endif             Wait                          Throw an exception if appropriate          ThrowIfExceptional  m resultWasSet               We shouldn t be here if the result has not been set          Contract Assert m resultWasSet   quot Task lt T gt  Result getter  Expected result to have been set  quot             return m result            internal set               Contract Assert m valueSelector    null   quot Task lt T gt  Result set  m valueSelector    null quot             if   TrySetResult value                         throw new InvalidOperationException Strings TaskT TransitionToFinal AlreadyCompleted                      If We call GetAwaiter method of Task  Task will wrapped TaskAwaiter lt TResult gt   Source code of GetAwaiter      Source code of TaskAwaiter    public TaskAwaiter GetAwaiter         return new TaskAwaiter this      And If We call GetResult   method of TaskAwaiter lt TResult gt   it will call Task Result property  that Task Result will call Wait   method of Task   Source code of GetResult     public TResult GetResult         TaskAwaiter ValidateEnd m task       return m task Result     It is source code of ValidateEnd Task task    Source code of ValidateEnd Task task     internal static void ValidateEnd Task task        if  task Status    TaskStatus RanToCompletion           HandleNonSuccess task      private static void HandleNonSuccess Task task        if   task IsCompleted                try   task Wait              catch               if  task Status    TaskStatus RanToCompletion                ThrowForNonSuccess task            This is my conclusion  As can be seen GetResult   is calling TaskAwaiter ValidateEnd       therefore Task Result is not same GetAwaiter GetResult    I think GetAwaiter   GetResult   is a beter choice instead of  Result because it don t wrap exceptions  I read this at page 582 in C  7 in a Nutshell  Joseph Albahari  amp  Ben Albahari  book  If an antecedent task faults  the exception is re-thrown when the continuation code calls  awaiter GetResult     Rather than calling GetResult   we could simply access the  Result property of the antecedent  The benefit of calling  GetResult is that if the antecedent faults  the exception is thrown directly without being wrapped in  AggregateException   allowing for simpler and cleaner catch blocks   Source  C  7 in a Nutshell s page 582

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https   github com aspnet Security issues 59      One last remark  you should avoid using Task Result and Task Wait as   much as possible as they always encapsulate the inner exception in an   AggregateException and replace the message by a generic one  One or   more errors occurred   which makes debugging harder  Even if the   synchronous version shouldn t be used that often  you should strongly   consider using Task GetAwaiter   GetResult   instead

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If a task faults  the exception is re-thrown when the continuation   code calls awaiter GetResult    Rather than calling GetResult  we   could simply access the Result property of the task  The benefit   of calling GetResult is that if the task faults  the exception is   thrown directly without being wrapped in AggregateException  allowing   for simpler and cleaner catch blocks       For nongeneric tasks  GetResult   has a void return value  Its useful   function is then solely to rethrow exceptions    source   c  7 0 in a Nutshell

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Pretty much  One small difference though  if the Task fails  GetResult   will just throw the exception caused directly  while Task Result will throw an AggregateException  However  what s the point of using either of those when it s async  The 100x better option is to use await   Also  you re not meant to use GetResult    It s meant to be for compiler use only  not for you  But if you don t want the annoying AggregateException  use it

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Task GetAwaiter   GetResult   is preferred over Task Wait and Task Result because it propagates exceptions rather than wrapping them in an AggregateException  However  all three methods cause the potential for deadlock and thread pool starvation issues  They should all be avoided in favor of async await  The quote below explains why Task Wait and Task Result don t simply contain the exception propagation behavior of Task GetAwaiter   GetResult    due to a  quot very high compatibility bar quot     As I mentioned previously  we have a very high compatibility bar  and thus we   ve avoided breaking changes  As such  Task Wait retains its original behavior of always wrapping   However  you may find yourself in some advanced situations where you want behavior similar to the synchronous blocking employed by Task Wait  but where you want the original exception propagated unwrapped rather than it being encased in an AggregateException   To achieve that  you can target the Task   s awaiter directly   When you write    await task      the compiler translates that into usage of the Task GetAwaiter   method  which returns an instance that has a GetResult   method   When used on a faulted Task  GetResult   will propagate the original exception  this is how    await task     gets its behavior    You can thus use    task GetAwaiter   GetResult      if you want to directly invoke this propagation logic   https   blogs msdn microsoft com pfxteam 2011 09 28 task-exception-handling-in-net-4-5      GetResult    actually means    check the task for errors    In general  I try my best to avoid synchronously blocking on an asynchronous task  However  there are a handful of situations where I do violate that guideline  In those rare conditions  my preferred method is GetAwaiter   GetResult   because it preserves the task exceptions instead of wrapping them in an AggregateException   http   blog stephencleary com 2014 12 a-tour-of-task-part-6-results html

[c#] Is Task.Result the same as .GetAwaiter.GetResult()?

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