Kindly help to provide one sample usage of loop.call_exception_handler(context) with an example in asyncio. When loop.get_exception_handler() is already present, why do someone need to call the exception handler explicitly. Also if loop.get_exception_handler() is not set, then what do loop.call_exception_handler(context) call.
call_exception_handler is a convenience function that encapsulates the logic of invoking the custom exception handler or the default exception handler, and of falling back to the default exception handler if the custom one itself fails. It is designed to be called from code that encounters an exception but doesn't have a "caller" to propagate it to. For example:
The handle that implements call_soon and call_later catches exceptions while invoking the provided function and uses call_exception_handler to report it.
The server part of the event loop code that calls accept in a loop uses call_exception_handler to report exceptions raised by accept. It cannot propagate the exception to its caller because it is running in a background task, so it has no caller.
Various parts of transports use call_exception_handler to report errors.
When loop.get_exception_handler() is already present, why do someone need to call the exception handler explicitly.
Because get_exception_handler() only invokes the custom exception handler, if one is set. If one is not set, the default exception handler is returned. And if one is set, and it raises an exception, the default exception handler is used to report that exception. And errors like SystemExit and KeyboardInterrupt are carefully ignored. It would be tedious and error-prone to repeat this logic in every place that needs to invoke the exception handler, so call_exception_handler was created.
Related
What is the best practice for handling exceptions in MassTransit 3+ with regard to Request/Response pattern? The docs here mention that if a ResponseAddress exists on a message, the Fault message will be sent to that address, but how does one consumer/receive the messages at that address? The ResponseAddress for Bus.Request seems to be an auto-generated MassTransit address that I don't have control over, so I don't know how to access the exception thrown in the main consumer. What am I missing? Here's my code to register the consumer and its fault consumer using Unity container:
cfg.ReceiveEndpoint(host, "request_response_queue", e =>
{
e.Consumer<IConsumer<IRequestResponse>>(container);
e.Consumer(() => container.Resolve<IMessageFaultConsumer<IRequestResponse>>() as IConsumer<Fault<IRequestResponse>>);
});
And here's my attempt at a global message fault consumer:
public interface IMessageFaultConsumer<TMessage>
{
}
public class MessageFaultConsumer<TMessage> : IConsumer<Fault<TMessage>>, IMessageFaultConsumer<TMessage>
{
public Task Consume(ConsumeContext<Fault<TMessage>> context)
{
Console.WriteLine("MessageFaultConsumer");
return Task.FromResult(0);
}
}
This approach DOES work when I use Bus.Publish as opposed to Bus.Request. I also looked into creating an IConsumeObserver and putting my global exception logging code into the ConsumeFault method, but that has the downside of being invoked every exception prior to the re-tries giving up. What is the proper way to handle exceptions for request/response?
First of all, the request/response support in MassTransit is meant to be used with the .Request() method, or the request client (MessageRequestClient or PublishRequestClient). With these methods, if the consumer of the request message throws an exception, that exception is packaged into the Fault<T>, which is sent to the ResponseAddress. Since the .Request() method, and the request client are both asynchronous, using await will throw an exception with the exception data from the fault included. That's how it is designed, await the request and it will either complete, timeout, or fault (throw an exception upon await).
If you are trying to put in some global "exception handler" code for logging purposes, you really should log those at the service boundary, and an observer is the best way to handle it. This way, you can just implement the ConsumeFault method, and log to your event sink. However, this is synchronous within the consumer pipeline, so recognize the delay that could be introduced.
The other option is to of course just consume Fault<T>, but as you mentioned, it does not get published when the request client is used with the response address in the header. In this case, perhaps your requester should publish an event indicating that operation X faulted, and you can log that -- at the business context level versus the service level.
There are many options here, it's just choosing the one that fits your use case best.
I'm trying to figure out whether using Window's
SetUnfilteredExceptionHandler will catch every exception in the process, or whether AddVectoredExceptionHandler will catch it before.
It seems that MSDN doesn't provide any info about the priority or the order of execution.
the first is called Vectored Exception Handling (VEH)
Vectored handlers are called in the order that they were added, after
the debugger gets a first chance notification, but before the system
begins unwinding the stack.
then (if exception not handled) called Frame-based Exception Handling (SEH)
the last (top level) exception handler in SEH can be supersede by SetUnhandledExceptionFilter
Enables an application to supersede the top-level exception handler of
each thread of a process.
lpTopLevelExceptionFilter is called last
I have an xamarin.android with xamarin.insights intergrated.
Right now every time I handle error manually (try/catch) I'm adding information about environment (staging/production):
try
{
ExceptionThrowingFunction();
}
catch (Exception exception)
{
exception.Data["Environment"] = "staging";
throw;
}
But this information is missing in case if error handled by xamarin.insights itself (in case of crash).
It is possible to add additional exception data in case of crash?
docs reference I used
From reading the docs page reference that you mentioned, I still get the impression that you have to call the .Report method as well as in:-
Insights.Report(exception, new Dictionary <string, string> {
{"Some additional info", "foobar"}
});
What I believe they are saying in this example:-
try {
ExceptionThrowingFunction();
}
catch (Exception exception) {
exception.Data["AccountType"] = "standard";
throw;
}
Is that you have the ability when any Exception is encountered, to package additional information that you can later send to the Insights server, as the Data property of the Exception is just a Key/Value Dictionary.
So if you had an Exception several layers deep, you can choose to re-throw the Exception with additional information contained within it that you will later send to the Insights server.
At a higher level, you can then take the Exception that was thrown deeper down the call-hierarchy and then call the Insights.Report, with:-
Insights.Report(
{the rethrown exception in your higher up try..catch block},
{rethrown exception}.Data
);
that will then send all the additional Key/Value information previously captured.
From seeing your last part of your question though it looks like you are interested in Insights handling and sending this additional .Data automatically should there be an unhandled exception.
If it is not currently being sent, then perhaps suggest to them that this can be sent also? As it sounds a feasible request for this to automatically be sent as well incase of an unhandled exception.
Update 1:-
Yes - I understand about the unhandled exception scenario now that you are referring to.
I have not dealt with this component directly, so there may be hooks / event handlers or something already defined where you can tap into this, and execute some custom code just prior to this being sent.
If this is not available, then perhaps suggest this to them to include as its a Beta product?
Alternatively, you could still achieve this yourself by capturing the unhandled exceptions just prior to them falling. You'd have to code this however on each platform.
For instance on Windows Phone in the App class there is Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e) to which you could then supplement the Exception thrown with this extra .Data.
For Android you could take a look at this post that describes how to catch uncaughtException that will help you in capturing the unhandled exceptions.
Whether just supplementing the Exception in these handlers above is enough all depends on how they've written their hook into this, as to how well it behaves and whether it is executed first, prior to their implementation.
You will have to try and see if it does. If it doesn't behave well, allowing you to supplement extra data prior to the automatic call to Insights, you have another fallback solution, to just do the .Report call manually within these unhandled exception handlers yourself to make this work and supplement the extra .Data to achieve your aim.
In our application we have error handling mechanism, where we throw runtime exceptions on an error. I noticed a strange behavior and I want to understand the mechanism underlying this one
1) Situation 1: Exception thrown from ServiceActivator is converted to MessageHandlingException
When an error occurs in a ServiceActivator, we throw an exception. The message we get on ErrorChannel has PayLoad as org.springframework.integration.MessageHandlingException and actual exception thrown as cause
2) Situation 2: Exception thrown from Filter is not masked with MessageHandlingException
When an error occurs in Filter, and we throw exception, then PayLoad is actual exception, and is not masked with org.springframework.integration.MessageHandlingException
I have a few questions:
Why exception throwing from ServiceActivator behaves differently than in Filter
Are there some "best practices" around error handling in Spring-integration projects, while utilizing the errorChannel and related infrastructure
Update 1:
Filter extends AbstractFileListFilter which is part of a filter chain- a custom CompositeFileFilter which implements FileListFilter
CompositeFileFilter is being used by a file:inbound-channel-adapter and which passes the output to a Channel declared below:
<int:channel
id="channelForFilesComingIn"
datatype="java.io.File"
>
<int:dispatcher task-executor="dispatchExecutor" />
</int:channel>
Update 2:
Whet we are trying to do is read files from filesystem and process them. In file reading part, using file:inbound-channel-adapter with a CompositeFilter which filters files which are not completely uploaded or don't meet naming standards.
After all filters pass, file is handed over to a ServiceActivator for processing
In any of above (Filter chain or Service) , if there is an error condition, it has to be reported to DB and by email. For achieving this we are throwing ApplicationException which are caught by errorChannel, and passed to specialized channels.
Just to make it clear, a MessageHandlingException is thrown (wraps user exception) when a Message HANDLER fails - a message handler is something that HANDLES a message.
If an exception is thrown in the MessageSource, there is no message yet so a MessageHandlingException (or any MessagingException) does not apply.
Instead, the poll fails and the exception is thrown back to the poller.
If you want to handle exceptions in a polled endpoint (MessageSource), you need to give the poller an ErrorHandlingTaskExecutor, to which you can provide an ErrorHandler and do what you want with the exception, but since there is no message yet, it is the original exception thrown by the MessageSource.
If you want to send it to the error channel, you'll need to do that in your custom ErrorHandler.
I register my own vectored exception handler, to catch and trace various exceptions in my application.
Sometimes I get an exception having 0x40010006 code, which is thrown by OutputDebugString function. Certainly, I'd like just to ignore it. What would be the appropriate return value in this case: EXCEPTION_CONTINUE_EXECUTION or EXCEPTION_CONTINUE_SEARCH?
You'll find exception codes listed in the ntstatus.h SDK header file. This one is DBG_PRINTEXCEPTION_C, some likelihood that you typed Ctrl+C to trigger it.
Exception codes with values less than 0x80000000 are just informal and never an indicator of real trouble. In general, you should never mess with exceptions that you don't recognize and don't want to explicitly handle. Let Windows continue searching for a handler by returning EXCEPTION_CONTINUE_SEARCH, the debugger will probably catch it in this case.