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Zac Sweers edited this page May 13, 2019
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Welcome to the RxDogTag wiki!
Consider the following trivial case of emitting an error with no error handling.
Observable.error(new RuntimeException("Unhandled error!"))
.subscribe();This results in a stacktrace like this:
io.reactivex.exceptions.OnErrorNotImplementedException: The exception was not handled due to missing onError handler in the subscribe() method call. Further reading: https://github.com/ReactiveX/RxJava/wiki/Error-Handling | Unhandled error!
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:704)
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:701)
at io.reactivex.internal.observers.LambdaObserver.onError(LambdaObserver.java:77)
at io.reactivex.internal.disposables.EmptyDisposable.error(EmptyDisposable.java:63)
at io.reactivex.internal.operators.observable.ObservableError.subscribeActual(ObservableError.java:38)
at io.reactivex.Observable.subscribe(Observable.java:12090)
at io.reactivex.Observable.subscribe(Observable.java:12076)
at io.reactivex.Observable.subscribe(Observable.java:11954)
at com.uber.anotherpackage.ReadMeExample.simpleSubscribe(ReadMeExample.java:26)
<collapsed internal calls>
Caused by: java.lang.RuntimeException: Unhandled error!
at com.uber.anotherpackage.ReadMeExample.simpleSubscribe(ReadMeExample.java:25)
... 25 more
Now let's look at the same example with tagging enabled:
io.reactivex.exceptions.OnErrorNotImplementedException: Unhandled error!
Caused by: java.lang.RuntimeException: Unhandled error!
at com.uber.anotherpackage.ReadMeExample.simpleSubscribe(ReadMeExample.java:26)
at [[ ↑↑ Inferred subscribe point ↑↑ ]].(:0)
at [[ ↓↓ Original trace ↓↓ ]].(:0)
at com.uber.anotherpackage.ReadMeExample.simpleSubscribe(ReadMeExample.java:25)
... 25 more
In the simple case, there's not much added benefit since the execution was synchronous and single threaded,
but you can see original trace has now been updated to indicate the exact line that subscribe() was called.
In this case: ReadMeExample.java:26.
To reduce noise - RxDogTag will wrap the original cause in a synthetic
OnErrorNotImplementedException. This uses the original cause's message and doesn't fill in the
stacktrace as it's irrelevant to the trace.
Consider a more complex example with threading:
Observable.just(1)
.subscribeOn(Schedulers.io())
.map(i -> null)
.subscribe();This is a fairly common case in RxJava concurrency. Without tagging, this yields the following trace:
io.reactivex.exceptions.OnErrorNotImplementedException: The exception was not handled due to missing onError handler in the subscribe() method call. Further reading: https://github.com/ReactiveX/RxJava/wiki/Error-Handling | The mapper function returned a null value.
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:704)
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:701)
at io.reactivex.internal.observers.LambdaObserver.onError(LambdaObserver.java:77)
at io.reactivex.internal.observers.BasicFuseableObserver.onError(BasicFuseableObserver.java:100)
at io.reactivex.internal.observers.BasicFuseableObserver.fail(BasicFuseableObserver.java:110)
at io.reactivex.internal.operators.observable.ObservableMap$MapObserver.onNext(ObservableMap.java:59)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeOnObserver.onNext(ObservableSubscribeOn.java:58)
at io.reactivex.internal.operators.observable.ObservableScalarXMap$ScalarDisposable.run(ObservableScalarXMap.java:248)
at io.reactivex.internal.operators.observable.ObservableJust.subscribeActual(ObservableJust.java:35)
at io.reactivex.Observable.subscribe(Observable.java:12090)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeTask.run(ObservableSubscribeOn.java:96)
at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:578)
at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66)
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException: The mapper function returned a null value.
at io.reactivex.internal.functions.ObjectHelper.requireNonNull(ObjectHelper.java:39)
at io.reactivex.internal.operators.observable.ObservableMap$MapObserver.onNext(ObservableMap.java:57)
... 14 more
Yikes! This is basically impossible to investigate if you're looking at a crash report from the wild.
Now the same trace with tagging enabled:
io.reactivex.exceptions.OnErrorNotImplementedException: The mapper function returned a null value.
Caused by: java.lang.NullPointerException: The mapper function returned a null value.
at com.uber.anotherpackage.ReadMeExample.complex(ReadMeExample.java:55)
at [[ ↑↑ Inferred subscribe point ↑↑ ]].(:0)
at [[ ↓↓ Original trace ↓↓ ]].(:0)
at io.reactivex.internal.functions.ObjectHelper.requireNonNull(ObjectHelper.java:39)
at io.reactivex.internal.operators.observable.ObservableMap$MapObserver.onNext(ObservableMap.java:57)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeOnObserver.onNext(ObservableSubscribeOn.java:58)
at io.reactivex.internal.operators.observable.ObservableScalarXMap$ScalarDisposable.run(ObservableScalarXMap.java:248)
at io.reactivex.internal.operators.observable.ObservableJust.subscribeActual(ObservableJust.java:35)
at io.reactivex.Observable.subscribe(Observable.java:12090)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeTask.run(ObservableSubscribeOn.java:96)
at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:578)
at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66)
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Now we have the example subscribe line at ReadMeExample.java:55. It may not be a silver bullet to
root-causing why the exception occurred, but at least you know where it's emanating from.
Let's look at one more example. This is similar to the previous, but instead of the exception occurring
upstream in the chain, the exception occurs in one of the observer callbacks; in this case - onNext.
Observable.just(1)
.subscribeOn(Schedulers.io())
.subscribe(i -> throwSomething());
private void throwSomething() {
throw new RuntimeException("Unhandled error!");
}Without tagging, this yields the following trace:
io.reactivex.exceptions.OnErrorNotImplementedException: The exception was not handled due to missing onError handler in the subscribe() method call. Further reading: https://github.com/ReactiveX/RxJava/wiki/Error-Handling | Unhandled error!
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:704)
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:701)
at io.reactivex.internal.observers.LambdaObserver.onError(LambdaObserver.java:77)
at io.reactivex.internal.observers.LambdaObserver.onNext(LambdaObserver.java:67)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeOnObserver.onNext(ObservableSubscribeOn.java:58)
at io.reactivex.internal.operators.observable.ObservableScalarXMap$ScalarDisposable.run(ObservableScalarXMap.java:248)
at io.reactivex.internal.operators.observable.ObservableJust.subscribeActual(ObservableJust.java:35)
at io.reactivex.Observable.subscribe(Observable.java:12090)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeTask.run(ObservableSubscribeOn.java:96)
at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:578)
at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66)
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.RuntimeException: Unhandled error!
at com.uber.anotherpackage.ReadMeExample.throwSomething(ReadMeExample.java:68)
at com.uber.anotherpackage.ReadMeExample.lambda$complexDelegate$1(ReadMeExample.java:63)
at io.reactivex.internal.observers.LambdaObserver.onNext(LambdaObserver.java:63)
... 14 more
Similar to the first example, this isn't terrible to root-cause. onNext is throwing a traceable
exception in this trivial case.
With tagging enabled:
io.reactivex.exceptions.OnErrorNotImplementedException: The exception was not handled due to missing onError handler in the subscribe() method call. Further reading: https://github.com/ReactiveX/RxJava/wiki/Error-Handling | Unhandled error!
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:704)
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:701)
at io.reactivex.internal.observers.LambdaObserver.onError(LambdaObserver.java:77)
at io.reactivex.internal.observers.LambdaObserver.onNext(LambdaObserver.java:67)
at com.uber.rxdogtag.DogTagObserver.lambda$onNext$3(DogTagObserver.java:53)
at com.uber.rxdogtag.RxDogTag.guardedDelegateCall(RxDogTag.java:262)
at com.uber.rxdogtag.DogTagObserver.onNext(DogTagObserver.java:53)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeOnObserver.onNext(ObservableSubscribeOn.java:58)
at io.reactivex.internal.operators.observable.ObservableScalarXMap$ScalarDisposable.run(ObservableScalarXMap.java:248)
at io.reactivex.internal.operators.observable.ObservableJust.subscribeActual(ObservableJust.java:35)
at io.reactivex.Observable.subscribe(Observable.java:12090)
at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeTask.run(ObservableSubscribeOn.java:96)
at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:578)
at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66)
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.RuntimeException: Unhandled error!
at com.uber.anotherpackage.ReadMeExample.complexDelegate(ReadMeExample.java:63)
at [[ ↑↑ Inferred subscribe point ↑↑ ]].(:0)
at [[ Originating callback: onNext ]].(:0)
at [[ ↓↓ Original trace ↓↓ ]].(:0)
at com.uber.anotherpackage.ReadMeExample.throwSomething(ReadMeExample.java:68)
at com.uber.anotherpackage.ReadMeExample.lambda$complexDelegate$1(ReadMeExample.java:63)
at io.reactivex.internal.observers.LambdaObserver.onNext(LambdaObserver.java:63)
... 17 more
Now we're given added context that this occurred in the onNext callback according to [[ Originating callback: onNext ]]
at the subscribe() call at ReadMeExample.java:63. This callback handling is supported for all the
standard callbacks and will report the correct name for each (onSuccess, onComplete, etc).
More information on LambdaConsumerIntrospection can be found in its implementation PR: https://github.com/ReactiveX/RxJava/pull/5590
Decision tree:
-> Is the observer an instance of `LambdaConsumerIntrospection`?
-> Does `hasCustomOnError()` return `false`?
-> Decorate with a DogTag observer.
In order to correctly identify which line is the subscribe() line, RxDogTag requires keeping the names of
any types in io.reactivex or com.uber.rxdogtag packages. This doesn't prevent shrinking unused
types, and as these are open source projects we don't think keeping these public risks any sort of
secret sauce. Keeping names has a negligible impact on APK size as well. If this is an issue for you
though, then RxDogTag is probably not the right solution for your project.
RxDogTag ships with custom rxdogtag.pro rules in the jar resources to handle this automatically.