Visual Studio ContextSwitchDeadlock

Question

I have been getting an error message that I can t resolve  It originates from Visual Studio or the debugger  I m not sure whether the ultimate error condition is in VS  the debugger  my program  or the database    This is a Windows app  Not a web app   First message from VS is a popup box saying   No symbols are loaded for any call stack frame  The source code can not be displayed   When that is clicked away  I get   ContextSwitchDeadlock was detected   along with a long message reproduced below   The error arises in a loop that scans down a DataTable  For each line  it uses a key  HIC    value from the table as a parameter for a SqlCommand  The command is used to create a SqlDataReader which returns one line  Data are compared  If an error is detected a row is added to a second DataTable   The error seems to be related to how long the procedure takes to run  i e  after 60 sec   not how many errors are found  I don t think it s a memory issue  No variables are declared within the loop  The only objects that are created are the SqlDataReaders  and they are in Using structures  Add System GC Collect   had no effect   The db is a SqlServer site on the same laptop   There are no fancy gizmos or gadgets on the Form   I am not aware of anything in this proc which is greatly different from what I ve done dozens of times before  I have seen the error before  but never on a consistent basis   Any ideas  anyone   Full error Text  The CLR has been unable to transition from COM context 0x1a0b88 to COM context 0x1a0cf8 for 60 seconds  The thread that owns the destination context apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages  This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time  To avoid this problem  all single threaded apartment  STA  threads should use pumping wait primitives  such as CoWaitForMultipleHandles  and routinely pump messages during long running operations

User · Answer

As Pedro said  you have an issue with the debugger preventing the message pump if you are stepping through code   But if you are performing a long running operation on the UI thread  then call Application DoEvents   which explicitly pumps the message queue and then returns control to your current method     However if you are doing this I would recommend at looking at your design so that you can perform processing off the UI thread so that your UI remains nice and snappy

User · Answer

It sounds like you are doing this on the main UI thread in the app   The UI thread is responsible for pumping windows messages as the arrive  and yet because yours is blocked in database calls it is unable to do so   This can cause problems with system wide messages   You should look at spawning a background thread for the long running operation and putting up some kind of  I m busy  dialog for the user while it happens

User · Answer

The ContextSwitchDeadlock doesn t necessarily mean your code has an issue  just that there is a potential   If you go to Debug  gt  Exceptions in the menu and expand the Managed Debugging Assistants  you will find ContextSwitchDeadlock is enabled   If you disable this  VS will no longer warn you when items are taking a long time to process   In some cases you may validly have a long-running operation   It s also helpful if you are debugging and have stopped on a line while this is processing - you don t want it to complain before you ve had a chance to dig into an issue

User · Answer

You can solve this by unchecking contextswitchdeadlock from  Debug- Exceptions     -  Expand MDA node -  uncheck -  contextswitchdeadlock

User · Answer

The above solution is good in some scenarios but there is another scenario where this happens when you are unit testing and you try to  Debug Selected Tests  from the Test Explorer when you solution is not set to Debug    In this case you need to change your solution from Release or whatever it is set to to Debug in this case  If this is the problem then changing  ContextSwitchDeadlock  won t really help you   I missed this myself because the error message was so nasty I didn t check the obvious thing which was the Debug setting

User · Answer

I was getting this error and switched the queries to async  await       ToListAsync     All good now

User · Answer

In Visual Studio 2017  unchecked the ContextSwitchDeadlock option by   Debug   Windows   Exception Settings    In Exception Setting Windows  Uncheck the ContextSwitchDeadlock option

User · Answer

If you don t want to disable this exception  all you need to do is to let your application pump some messages at least once every 60 seconds  It will prevent this exception to happen  Try calling System Threading Thread CurrentThread Join 10  once in a while  There are other calls you can do that let the messages pump

User · Answer

In Visual Studio 2017 Spanish version        Depurar  -   Ventanas  -   Configuraci  n de Excepciones    and search  ContextSwitchDeadlock    Then  uncheck it   Or shortcut      Ctrl D E   Best

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