Calling async method synchronously

Question

I have an async method   public async Task lt string gt  GenerateCodeAsync         string code   await GenerateCodeService GenerateCodeAsync        return code      I need to call this method from a synchronous method   How can I do this without having to duplicate the GenerateCodeAsync method in order for this to work synchronously   Update  Yet no reasonable solution found   However  i see that HttpClient already implements this pattern  using  HttpClient client   new HttpClient             async     HttpResponseMessage responseAsync   await client GetAsync url           sync     HttpResponseMessage responseSync   client GetAsync url  Result

User · Answer

I prefer a non blocking approach               Dim aw1 GenerateCodeAsync   GetAwaiter               While Not aw1 IsCompleted                 Application DoEvents               End While

User · Answer

I need to call this method from a synchronously method    It s possible with GenerateCodeAsync   Result or GenerateCodeAsync   Wait    as the other answer suggests  This would block the current thread until GenerateCodeAsync has completed   However  your question is tagged with asp net  and you also left the comment      I was hoping for a simpler solution  thinking that asp net handled   this much easier than writing so many lines of code   My point is  you should not be blocking on an asynchronous method in ASP NET  This will reduce the scalability of your web app  and may create a deadlock  when an await continuation inside GenerateCodeAsync is posted to AspNetSynchronizationContext   Using Task Run      Result to offload something to a pool thread and then block will hurt the scalability even more  as it incurs  1 more thread to process a given HTTP request   ASP NET has built-in support for asynchronous methods  either through asynchronous controllers  in ASP NET MVC and Web API  or directly via AsyncManager and PageAsyncTask in classic ASP NET  You should use it  For more details  check this answer

User · Answer

If you have an async method called   RefreshList   then  you can call that async method from a non-async method like below   Task Run async      gt    await RefreshList

User · Answer

You can access the Result property of the task  which will cause your thread to block until the result is available   string code   GenerateCodeAsync   Result      Note  In some cases  this might lead to a deadlock  Your call to Result blocks the main thread  thereby preventing the remainder of the async code to execute  You have the following options to make sure that this doesn t happen    Add  ConfigureAwait false  to your library method or explicitly execute your async method in a thread pool thread and wait for it to finish   string code   Task Run GenerateCodeAsync  Result     This does not mean that you should just mindlessly add  ConfigureAwait false  after all your async calls  For a detailed analysis on why and when you should use  ConfigureAwait false   see the following blog post     NET Blog  ConfigureAwait FAQ

User · Answer

Most of the answers on this thread are either complex or will result in deadlock   Following method is simple and it will avoid deadlock because we are waiting for the task to finish and only then getting its result-  var task   Task Run      gt  GenerateCodeAsync      task Wait    string code   task Result    Furthermore  here is a reference to MSDN article that talks about exactly same thing- https   blogs msdn microsoft com jpsanders 2017 08 28 asp-net-do-not-use-task-result-in-main-context

User · Answer

You should get the awaiter  GetAwaiter    and end the wait for the completion of the asynchronous task  GetResult      string code   GenerateCodeAsync   GetAwaiter   GetResult

User · Answer

To prevent deadlocks I always try to use Task Run   when I have to call an async method synchronously that  Heinzi mentions   However the method has to be modified if the async method uses parameters  For example Task Run GenerateCodeAsync  test    Result gives the error      Argument 1  cannot convert from  System Threading Tasks Task lt string gt     to  System Action    This could be called like this instead   string code   Task Run      gt  GenerateCodeAsync  test    Result

User · Answer

Well I am using this approach       private string RunSync                 var task   Task Run async      gt  await GenerateCodeService GenerateCodeAsync             if  task IsFaulted  amp  amp  task Exception    null                        throw task Exception                     return task Result

User · Answer

Microsoft Identity has extension methods which call async methods synchronously  For example there is GenerateUserIdentityAsync   method and equal CreateIdentity    If you look at UserManagerExtensions CreateIdentity   it look like this    public static ClaimsIdentity CreateIdentity lt TUser  TKey gt  this UserManager lt TUser  TKey gt  manager  TUser user          string authenticationType          where TKey   IEquatable lt TKey gt          where TUser   class  IUser lt TKey gt                if  manager    null                        throw new ArgumentNullException  manager                      return AsyncHelper RunSync      gt  manager CreateIdentityAsync user  authenticationType            Now lets see what AsyncHelper RunSync does    public static TResult RunSync lt TResult gt  Func lt Task lt TResult gt  gt  func                var cultureUi   CultureInfo CurrentUICulture          var culture   CultureInfo CurrentCulture          return  myTaskFactory StartNew      gt                        Thread CurrentThread CurrentCulture   culture              Thread CurrentThread CurrentUICulture   cultureUi              return func               Unwrap   GetAwaiter   GetResult            So  this is your wrapper for async method  And please don t read data from Result - it will potentially block your code in ASP    There is another way - which is suspicious for me  but you can consider it too    Result r   null               YourAsyncMethod                    ContinueWith t   gt                                        r   t Result                                      Wait

User · Answer

EDIT   Task has Wait method  Task Wait    which waits for the  promise  to resolve and then continues  thus rendering it synchronous   example    async Task lt String gt  MyAsyncMethod            String mySyncMethod          return MyAsyncMethod   Wait

User · Answer

You should be able to get this done using delegates  lambda expression  private void button2 Click object sender  EventArgs e                 label1 Text    waiting                Task lt string gt  sCode   Task Run async      gt                        string msg  await GenerateCodeAsync                return msg                       label1 Text    sCode Result              private Task lt string gt  GenerateCodeAsync                 return Task Run lt string gt       gt  GenerateCode                private string GenerateCode                 Thread Sleep 2000           return  I m back

User · Answer

How about some extension methods that asynchronously await the completion of the asynchronous operation  then set a ManualResetEvent to indicate completion  NOTE  You can use Task Run    however extension methods are a cleaner interface for expressing what you really want  Tests showing how to use the extensions       TestClass      public class TaskExtensionsTests                TestMethod          public void AsynchronousOperationWithNoResult                         SampleAsynchronousOperationWithNoResult   AwaitResult                        TestMethod          public void AsynchronousOperationWithResult                         Assert AreEqual 3  SampleAsynchronousOperationWithResult 3  AwaitResult                         TestMethod           ExpectedException typeof Exception            public void AsynchronousOperationWithNoResultThrows                         SampleAsynchronousOperationWithNoResultThrows   AwaitResult                        TestMethod           ExpectedException typeof Exception            public void AsynchronousOperationWithResultThrows                         SampleAsynchronousOperationWithResultThrows 3  AwaitResult                       private static async Task SampleAsynchronousOperationWithNoResult                         await Task Yield                       private static async Task lt T gt  SampleAsynchronousOperationWithResult lt T gt  T result                        await Task Yield                return result                     private static async Task SampleAsynchronousOperationWithNoResultThrows                         await Task Yield                throw new Exception                       private static async Task lt T gt  SampleAsynchronousOperationWithResultThrows lt T gt  T result                        await Task Yield                throw new Exception                        TestMethod          public void AsynchronousValueOperationWithNoResult                         SampleAsynchronousValueOperationWithNoResult   AwaitResult                        TestMethod          public void AsynchronousValueOperationWithResult                         Assert AreEqual 3  SampleAsynchronousValueOperationWithResult 3  AwaitResult                         TestMethod           ExpectedException typeof Exception            public void AsynchronousValueOperationWithNoResultThrows                         SampleAsynchronousValueOperationWithNoResultThrows   AwaitResult                        TestMethod           ExpectedException typeof Exception            public void AsynchronousValueOperationWithResultThrows                         SampleAsynchronousValueOperationWithResultThrows 3  AwaitResult                       private static async ValueTask SampleAsynchronousValueOperationWithNoResult                         await Task Yield                       private static async ValueTask lt T gt  SampleAsynchronousValueOperationWithResult lt T gt  T result                        await Task Yield                return result                     private static async ValueTask SampleAsynchronousValueOperationWithNoResultThrows                         await Task Yield                throw new Exception                       private static async ValueTask lt T gt  SampleAsynchronousValueOperationWithResultThrows lt T gt  T result                        await Task Yield                throw new Exception                     The extensions          lt summary gt          Defines extension methods for  lt see cref  quot Task quot   gt  and  lt see cref  quot ValueTask quot   gt            lt  summary gt      public static class TaskExtensions                    lt summary gt              Synchronously await the results of an asynchronous operation without deadlocking  ignoring cancellation               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot Task quot   gt  representing the pending operation               lt  param gt          public static void AwaitCompletion this ValueTask task                        new SynchronousAwaiter task  true  GetResult                            lt summary gt              Synchronously await the results of an asynchronous operation without deadlocking  ignoring cancellation               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot Task quot   gt  representing the pending operation               lt  param gt          public static void AwaitCompletion this Task task                        new SynchronousAwaiter task  true  GetResult                            lt summary gt              Synchronously await the results of an asynchronous operation without deadlocking               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot Task quot   gt  representing the pending operation               lt  param gt               lt typeparam name  quot T quot  gt              The result type of the operation               lt  typeparam gt               lt returns gt              The result of the operation               lt  returns gt          public static T AwaitResult lt T gt  this Task lt T gt  task                        return new SynchronousAwaiter lt T gt  task  GetResult                            lt summary gt              Synchronously await the results of an asynchronous operation without deadlocking               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot Task quot   gt  representing the pending operation               lt  param gt          public static void AwaitResult this Task task                        new SynchronousAwaiter task  GetResult                            lt summary gt              Synchronously await the results of an asynchronous operation without deadlocking               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot ValueTask quot   gt  representing the pending operation               lt  param gt               lt typeparam name  quot T quot  gt              The result type of the operation               lt  typeparam gt               lt returns gt              The result of the operation               lt  returns gt          public static T AwaitResult lt T gt  this ValueTask lt T gt  task                        return new SynchronousAwaiter lt T gt  task  GetResult                            lt summary gt              Synchronously await the results of an asynchronous operation without deadlocking               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot ValueTask quot   gt  representing the pending operation               lt  param gt          public static void AwaitResult this ValueTask task                        new SynchronousAwaiter task  GetResult                            lt summary gt              Ignore the  lt see cref  quot OperationCanceledException quot   gt  if the operation is cancelled               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot Task quot   gt  representing the asynchronous operation whose cancellation is to be ignored               lt  param gt               lt returns gt              The  lt see cref  quot Task quot   gt  representing the asynchronous operation whose cancellation is ignored               lt  returns gt          public static async Task IgnoreCancellationResult this Task task                        try                               await task ConfigureAwait false                             catch  OperationCanceledException                                                      lt summary gt              Ignore the  lt see cref  quot OperationCanceledException quot   gt  if the operation is cancelled               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot ValueTask quot   gt  representing the asynchronous operation whose cancellation is to be ignored               lt  param gt               lt returns gt              The  lt see cref  quot ValueTask quot   gt  representing the asynchronous operation whose cancellation is ignored               lt  returns gt          public static async ValueTask IgnoreCancellationResult this ValueTask task                        try                               await task ConfigureAwait false                             catch  OperationCanceledException                                                      lt summary gt              Ignore the results of an asynchronous operation allowing it to run and die silently in the background               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot Task quot   gt  representing the asynchronous operation whose results are to be ignored               lt  param gt          public static async void IgnoreResult this Task task                        try                               await task ConfigureAwait false                             catch                                  ignore exceptions                                       lt summary gt              Ignore the results of an asynchronous operation allowing it to run and die silently in the background               lt  summary gt               lt param name  quot task quot  gt              The  lt see cref  quot ValueTask quot   gt  representing the asynchronous operation whose results are to be ignored               lt  param gt          public static async void IgnoreResult this ValueTask task                        try                               await task ConfigureAwait false                             catch                                  ignore exceptions                                         lt summary gt          Internal class for waiting for asynchronous operations that have a result           lt  summary gt           lt typeparam name  quot TResult quot  gt          The result type           lt  typeparam gt      public class SynchronousAwaiter lt TResult gt                     lt summary gt              The manual reset event signaling completion               lt  summary gt          private readonly ManualResetEvent manualResetEvent                lt summary gt              The exception thrown by the asynchronous operation               lt  summary gt          private Exception exception                lt summary gt              The result of the asynchronous operation               lt  summary gt          private TResult result                lt summary gt              Initializes a new instance of the  lt see cref  quot SynchronousAwaiter TResult  quot   gt  class               lt  summary gt               lt param name  quot task quot  gt              The task representing an asynchronous operation               lt  param gt          public SynchronousAwaiter Task lt TResult gt  task                        this manualResetEvent   new ManualResetEvent false               this WaitFor task                           lt summary gt              Initializes a new instance of the  lt see cref  quot SynchronousAwaiter TResult  quot   gt  class               lt  summary gt               lt param name  quot task quot  gt              The task representing an asynchronous operation               lt  param gt          public SynchronousAwaiter ValueTask lt TResult gt  task                        this manualResetEvent   new ManualResetEvent false               this WaitFor task                           lt summary gt              Gets a value indicating whether the operation is complete               lt  summary gt          public bool IsComplete   gt  this manualResetEvent WaitOne 0                 lt summary gt              Synchronously get the result of an asynchronous operation               lt  summary gt               lt returns gt              The result of the asynchronous operation               lt  returns gt          public TResult GetResult                         this manualResetEvent WaitOne                return this exception    null   throw this exception   this result                          lt summary gt              Tries to synchronously get the result of an asynchronous operation               lt  summary gt               lt param name  quot operationResult quot  gt              The result of the operation               lt  param gt               lt returns gt              The result of the asynchronous operation               lt  returns gt          public bool TryGetResult out TResult operationResult                        if  this IsComplete                                operationResult   this exception    null   throw this exception   this result                  return true                             operationResult   default              return false                          lt summary gt              Background  quot thread quot  which waits for the specified asynchronous operation to complete               lt  summary gt               lt param name  quot task quot  gt              The task               lt  param gt          private async void WaitFor Task lt TResult gt  task                        try                               this result   await task ConfigureAwait false                             catch  Exception exception                                this exception   exception                            finally                               this manualResetEvent Set                                          lt summary gt              Background  quot thread quot  which waits for the specified asynchronous operation to complete               lt  summary gt               lt param name  quot task quot  gt              The task               lt  param gt          private async void WaitFor ValueTask lt TResult gt  task                        try                               this result   await task ConfigureAwait false                             catch  Exception exception                                this exception   exception                            finally                               this manualResetEvent Set                                            lt summary gt          Internal class for  waiting for  asynchronous operations that have no result           lt  summary gt      public class SynchronousAwaiter                    lt summary gt              The manual reset event signaling completion               lt  summary gt          private readonly ManualResetEvent manualResetEvent   new ManualResetEvent false                 lt summary gt              The exception thrown by the asynchronous operation               lt  summary gt          private Exception exception                lt summary gt              Initializes a new instance of the  lt see cref  quot SynchronousAwaiter TResult  quot   gt  class               lt  summary gt               lt param name  quot task quot  gt              The task representing an asynchronous operation               lt  param gt               lt param name  quot ignoreCancellation quot  gt              Indicates whether to ignore cancellation  Default is false               lt  param gt          public SynchronousAwaiter Task task  bool ignoreCancellation   false                        this manualResetEvent   new ManualResetEvent false               this WaitFor task  ignoreCancellation                           lt summary gt              Initializes a new instance of the  lt see cref  quot SynchronousAwaiter TResult  quot   gt  class               lt  summary gt               lt param name  quot task quot  gt              The task representing an asynchronous operation               lt  param gt               lt param name  quot ignoreCancellation quot  gt              Indicates whether to ignore cancellation  Default is false               lt  param gt          public SynchronousAwaiter ValueTask task  bool ignoreCancellation   false                        this manualResetEvent   new ManualResetEvent false               this WaitFor task  ignoreCancellation                           lt summary gt              Gets a value indicating whether the operation is complete               lt  summary gt          public bool IsComplete   gt  this manualResetEvent WaitOne 0                 lt summary gt              Synchronously get the result of an asynchronous operation               lt  summary gt          public void GetResult                         this manualResetEvent WaitOne                if  this exception    null                                throw this exception                                        lt summary gt              Background  quot thread quot  which waits for the specified asynchronous operation to complete               lt  summary gt               lt param name  quot task quot  gt              The task               lt  param gt               lt param name  quot ignoreCancellation quot  gt              Indicates whether to ignore cancellation  Default is false               lt  param gt          private async void WaitFor Task task  bool ignoreCancellation                        try                               await task ConfigureAwait false                             catch  OperationCanceledException                                          catch  Exception exception                                this exception   exception                            finally                               this manualResetEvent Set                                          lt summary gt              Background  quot thread quot  which waits for the specified asynchronous operation to complete               lt  summary gt               lt param name  quot task quot  gt                  The task               lt  param gt               lt param name  quot ignoreCancellation quot  gt              Indicates whether to ignore cancellation  Default is false               lt  param gt          private async void WaitFor ValueTask task  bool ignoreCancellation                        try                               await task ConfigureAwait false                             catch  OperationCanceledException                                          catch  Exception exception                                this exception   exception                            finally                               this manualResetEvent Set

[c#] Calling async method synchronously

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