What s the difference between Invoke and BeginInvoke

Question

Just wondering what the difference between BeginInvoke   and Invoke   are    Mainly what each one would be used for   EDIT  What is the difference between creating a threading object and calling invoke on that and just calling BeginInvoke   on a delegate  or are they the same thing

User · Answer

Building on Jon Skeet s reply  there are times when you want to invoke a delegate and wait for its execution to complete before the current thread continues   In those cases the Invoke call is what you want   In multi-threading applications  you may not want a thread to wait on a delegate to finish execution  especially if that delegate performs I O  which could make the delegate and your thread block    In those cases the BeginInvoke would be useful   By calling it  you re telling the delegate to start but then your thread is free to do other things in parallel with the delegate   Using BeginInvoke increases the complexity of your code but there are times when the improved performance is worth the complexity

User · Answer

Do you mean Delegate Invoke BeginInvoke or Control Invoke BeginInvoke    Delegate Invoke  Executes synchronously  on the same thread  Delegate BeginInvoke  Executes asynchronously  on a threadpool thread  Control Invoke  Executes on the UI thread  but calling thread waits for completion before continuing  Control BeginInvoke  Executes on the UI thread  and calling thread doesn t wait for completion    Tim s answer mentions when you might want to use BeginInvoke - although it was mostly geared towards Delegate BeginInvoke  I suspect   For Windows Forms apps  I would suggest that you should usually use BeginInvoke  That way you don t need to worry about deadlock  for example - but you need to understand that the UI may not have been updated by the time you next look at it  In particular  you shouldn t modify data which the UI thread might be about to use for display purposes  For example  if you have a Person with FirstName and LastName properties  and you did   person FirstName    Kevin      person is a shared reference person LastName    Spacey   control BeginInvoke UpdateName   person FirstName    Keyser   person LastName    Soze     Then the UI may well end up displaying  Keyser Spacey    There s an outside chance it could display  Kevin Soze  but only through the weirdness of the memory model    Unless you have this sort of issue  however  Control BeginInvoke is easier to get right  and will avoid your background thread from having to wait for no good reason  Note that the Windows Forms team has guaranteed that you can use Control BeginInvoke in a  fire and forget  manner - i e  without ever calling EndInvoke  This is not true of async calls in general  normally every BeginXXX should have a corresponding EndXXX call  usually in the callback

User · Answer

Do you mean Delegate Invoke BeginInvoke or Control Invoke BeginInvoke    Delegate Invoke  Executes synchronously  on the same thread  Delegate BeginInvoke  Executes asynchronously  on a threadpool thread  Control Invoke  Executes on the UI thread  but calling thread waits for completion before continuing  Control BeginInvoke  Executes on the UI thread  and calling thread doesn t wait for completion    Tim s answer mentions when you might want to use BeginInvoke - although it was mostly geared towards Delegate BeginInvoke  I suspect   For Windows Forms apps  I would suggest that you should usually use BeginInvoke  That way you don t need to worry about deadlock  for example - but you need to understand that the UI may not have been updated by the time you next look at it  In particular  you shouldn t modify data which the UI thread might be about to use for display purposes  For example  if you have a Person with FirstName and LastName properties  and you did   person FirstName    Kevin      person is a shared reference person LastName    Spacey   control BeginInvoke UpdateName   person FirstName    Keyser   person LastName    Soze     Then the UI may well end up displaying  Keyser Spacey    There s an outside chance it could display  Kevin Soze  but only through the weirdness of the memory model    Unless you have this sort of issue  however  Control BeginInvoke is easier to get right  and will avoid your background thread from having to wait for no good reason  Note that the Windows Forms team has guaranteed that you can use Control BeginInvoke in a  fire and forget  manner - i e  without ever calling EndInvoke  This is not true of async calls in general  normally every BeginXXX should have a corresponding EndXXX call  usually in the callback

User · Answer

Just to give a short  working example to see an effect of their difference  new Thread foo  Start     private void foo       this Dispatcher BeginInvoke DispatcherPriority Normal       ThreadStart delegate                 myTextBox Text    bing           Thread Sleep TimeSpan FromSeconds 3              MessageBox Show  done        If use BeginInvoke  MessageBox pops simultaneous to the text update  If use Invoke  MessageBox pops after the 3 second sleep  Hence  showing the effect of an asynchronous  BeginInvoke  and a synchronous  Invoke  call

User · Answer

The difference between Control Invoke   and Control BeginInvoke   is    BeginInvoke   will schedule the asynchronous action on the GUI thread  When the asynchronous action is scheduled  your code continues  Some time later  you don t know exactly when  your asynchronous action will be executed Invoke   will execute your asynchronous action  on the GUI thread  and wait until your action has completed    A logical conclusion is that a delegate you pass to Invoke   can have out-parameters or a return-value  while a delegate you pass to BeginInvoke   cannot  you have to use EndInvoke to retrieve the results

User · Answer

Building on Jon Skeet s reply  there are times when you want to invoke a delegate and wait for its execution to complete before the current thread continues   In those cases the Invoke call is what you want   In multi-threading applications  you may not want a thread to wait on a delegate to finish execution  especially if that delegate performs I O  which could make the delegate and your thread block    In those cases the BeginInvoke would be useful   By calling it  you re telling the delegate to start but then your thread is free to do other things in parallel with the delegate   Using BeginInvoke increases the complexity of your code but there are times when the improved performance is worth the complexity

User · Answer

Just adding why and when to use Invoke     Both Invoke   and BeginInvoke   marshal the code you specify to the dispatcher thread   But unlike BeginInvoke    Invoke   stalls your thread until the dispatcher executes your code  You might want to use Invoke   if you need to pause an asynchronous operation until the user has supplied some sort of feedback   For example  you could call Invoke   to run a snippet of code that shows an OK Cancel dialog box  After the user clicks a button and your marshaled code completes  the invoke   method will return  and you can act upon the user s response    See Pro WPF in C  chapter 31

User · Answer

Just to give a short  working example to see an effect of their difference  new Thread foo  Start     private void foo       this Dispatcher BeginInvoke DispatcherPriority Normal       ThreadStart delegate                 myTextBox Text    bing           Thread Sleep TimeSpan FromSeconds 3              MessageBox Show  done        If use BeginInvoke  MessageBox pops simultaneous to the text update  If use Invoke  MessageBox pops after the 3 second sleep  Hence  showing the effect of an asynchronous  BeginInvoke  and a synchronous  Invoke  call

User · Answer

Delegate BeginInvoke   asynchronously queues the call of a delegate and returns control immediately   When using Delegate BeginInvoke    you should call Delegate EndInvoke   in the callback method to get the results   Delegate Invoke   synchronously calls the delegate in the same thread   MSDN Article

User · Answer

Delegate BeginInvoke   asynchronously queues the call of a delegate and returns control immediately   When using Delegate BeginInvoke    you should call Delegate EndInvoke   in the callback method to get the results   Delegate Invoke   synchronously calls the delegate in the same thread   MSDN Article

User · Answer

Do you mean Delegate Invoke BeginInvoke or Control Invoke BeginInvoke    Delegate Invoke  Executes synchronously  on the same thread  Delegate BeginInvoke  Executes asynchronously  on a threadpool thread  Control Invoke  Executes on the UI thread  but calling thread waits for completion before continuing  Control BeginInvoke  Executes on the UI thread  and calling thread doesn t wait for completion    Tim s answer mentions when you might want to use BeginInvoke - although it was mostly geared towards Delegate BeginInvoke  I suspect   For Windows Forms apps  I would suggest that you should usually use BeginInvoke  That way you don t need to worry about deadlock  for example - but you need to understand that the UI may not have been updated by the time you next look at it  In particular  you shouldn t modify data which the UI thread might be about to use for display purposes  For example  if you have a Person with FirstName and LastName properties  and you did   person FirstName    Kevin      person is a shared reference person LastName    Spacey   control BeginInvoke UpdateName   person FirstName    Keyser   person LastName    Soze     Then the UI may well end up displaying  Keyser Spacey    There s an outside chance it could display  Kevin Soze  but only through the weirdness of the memory model    Unless you have this sort of issue  however  Control BeginInvoke is easier to get right  and will avoid your background thread from having to wait for no good reason  Note that the Windows Forms team has guaranteed that you can use Control BeginInvoke in a  fire and forget  manner - i e  without ever calling EndInvoke  This is not true of async calls in general  normally every BeginXXX should have a corresponding EndXXX call  usually in the callback

User · Answer

Building on Jon Skeet s reply  there are times when you want to invoke a delegate and wait for its execution to complete before the current thread continues   In those cases the Invoke call is what you want   In multi-threading applications  you may not want a thread to wait on a delegate to finish execution  especially if that delegate performs I O  which could make the delegate and your thread block    In those cases the BeginInvoke would be useful   By calling it  you re telling the delegate to start but then your thread is free to do other things in parallel with the delegate   Using BeginInvoke increases the complexity of your code but there are times when the improved performance is worth the complexity

User · Answer

Delegate BeginInvoke   asynchronously queues the call of a delegate and returns control immediately   When using Delegate BeginInvoke    you should call Delegate EndInvoke   in the callback method to get the results   Delegate Invoke   synchronously calls the delegate in the same thread   MSDN Article

User · Answer

Just adding why and when to use Invoke     Both Invoke   and BeginInvoke   marshal the code you specify to the dispatcher thread   But unlike BeginInvoke    Invoke   stalls your thread until the dispatcher executes your code  You might want to use Invoke   if you need to pause an asynchronous operation until the user has supplied some sort of feedback   For example  you could call Invoke   to run a snippet of code that shows an OK Cancel dialog box  After the user clicks a button and your marshaled code completes  the invoke   method will return  and you can act upon the user s response    See Pro WPF in C  chapter 31

User · Answer

Delegate BeginInvoke   asynchronously queues the call of a delegate and returns control immediately   When using Delegate BeginInvoke    you should call Delegate EndInvoke   in the callback method to get the results   Delegate Invoke   synchronously calls the delegate in the same thread   MSDN Article

User · Answer

The difference between Control Invoke   and Control BeginInvoke   is    BeginInvoke   will schedule the asynchronous action on the GUI thread  When the asynchronous action is scheduled  your code continues  Some time later  you don t know exactly when  your asynchronous action will be executed Invoke   will execute your asynchronous action  on the GUI thread  and wait until your action has completed    A logical conclusion is that a delegate you pass to Invoke   can have out-parameters or a return-value  while a delegate you pass to BeginInvoke   cannot  you have to use EndInvoke to retrieve the results

User · Answer

Do you mean Delegate Invoke BeginInvoke or Control Invoke BeginInvoke    Delegate Invoke  Executes synchronously  on the same thread  Delegate BeginInvoke  Executes asynchronously  on a threadpool thread  Control Invoke  Executes on the UI thread  but calling thread waits for completion before continuing  Control BeginInvoke  Executes on the UI thread  and calling thread doesn t wait for completion    Tim s answer mentions when you might want to use BeginInvoke - although it was mostly geared towards Delegate BeginInvoke  I suspect   For Windows Forms apps  I would suggest that you should usually use BeginInvoke  That way you don t need to worry about deadlock  for example - but you need to understand that the UI may not have been updated by the time you next look at it  In particular  you shouldn t modify data which the UI thread might be about to use for display purposes  For example  if you have a Person with FirstName and LastName properties  and you did   person FirstName    Kevin      person is a shared reference person LastName    Spacey   control BeginInvoke UpdateName   person FirstName    Keyser   person LastName    Soze     Then the UI may well end up displaying  Keyser Spacey    There s an outside chance it could display  Kevin Soze  but only through the weirdness of the memory model    Unless you have this sort of issue  however  Control BeginInvoke is easier to get right  and will avoid your background thread from having to wait for no good reason  Note that the Windows Forms team has guaranteed that you can use Control BeginInvoke in a  fire and forget  manner - i e  without ever calling EndInvoke  This is not true of async calls in general  normally every BeginXXX should have a corresponding EndXXX call  usually in the callback

User · Answer

Building on Jon Skeet s reply  there are times when you want to invoke a delegate and wait for its execution to complete before the current thread continues   In those cases the Invoke call is what you want   In multi-threading applications  you may not want a thread to wait on a delegate to finish execution  especially if that delegate performs I O  which could make the delegate and your thread block    In those cases the BeginInvoke would be useful   By calling it  you re telling the delegate to start but then your thread is free to do other things in parallel with the delegate   Using BeginInvoke increases the complexity of your code but there are times when the improved performance is worth the complexity

[c#] What's the difference between Invoke() and BeginInvoke()

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