PowerShell language worker support for cancellation token that is emitted by the function host.

[Ritika259]

There is a scenario where one was getting "Task Cancelled exception " in PowerShell functions.

Entire exception trace:

System.Threading.Tasks.TaskCanceledException : A task was canceled.
   at async Microsoft.Azure.WebJobs.Script.Description.WorkerFunctionInvoker.InvokeCore(Object[] parameters,FunctionInvocationContext context) at //src/WebJobs.Script/Description/Workers/WorkerFunctionInvoker.cs : 96
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Script.Description.FunctionInvokerBase.Invoke(Object[] parameters) at //src/WebJobs.Script/Description/FunctionInvokerBase.cs : 82
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Executors.VoidTaskMethodInvoker2.InvokeAsync[TReflected,TReturnType](TReflected instance,Object[] arguments) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\VoidTaskMethodInvoker.cs : 20    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()    at async Microsoft.Azure.WebJobs.Host.Executors.FunctionInvoker2.InvokeAsync[TReflected,TReturnValue](Object instance,Object[] arguments) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionInvoker.cs : 52
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.InvokeWithTimeoutAsync(IFunctionInvoker invoker,ParameterHelper parameterHelper,CancellationTokenSource timeoutTokenSource,CancellationTokenSource functionCancellationTokenSource,Boolean throwOnTimeout,TimeSpan timerInterval,IFunctionInstance instance) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs : 581
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithWatchersAsync(IFunctionInstanceEx instance,ParameterHelper parameterHelper,ILogger logger,CancellationTokenSource functionCancellationTokenSource) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs : 527
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstanceEx instance,FunctionStartedMessage message,FunctionInstanceLogEntry instanceLogEntry,ParameterHelper parameterHelper,ILogger logger,CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs : 306
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstanceEx instance,FunctionStartedMessage message,FunctionInstanceLogEntry instanceLogEntry,ParameterHelper parameterHelper,ILogger logger,CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs : 352
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.TryExecuteAsync(IFunctionInstance functionInstance,CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs : 108

I could see that at the time of failure, there were no worker processes ( powershell processes ) getting assigned to the invocations.
However, when we see for successful executions, there are processes attached correctly. Invocation Response received correctly

Since this is a queue trigger message, so the messages are getting retried and no loss of functionality... 

To remediate this, there was a suggestion to handle the cancellation token as mentioned here ( this is for .Net ):
Improve error handling for invocation request cancellations · Issue #8986 · Azure/azure-functions-host (github.com)

However, the powershell language worker hasn't been ready to support cancellation token that is emitted by the function host.
as per https://github.com/Azure/azure-functions-host/wiki/Out-of-proc-Support-for-Cancellation-Tokens

Requesting you to please create a roadmap for this feature.

Looping in @AnatoliB , Thank you for the information.