Completable.subscribe() swallows errors by default

[kotucz]

The default behavior of Completable.subscribe() for errors is different from that of Observable or Single. Errors in Completable are just passed to RxJavaErrorHandler which does nothing by default. While Observable and Single cause runtime OnErrorNotImplementedException which is expected.

Completable.java

        @Override
        public void onError(Throwable e) {
            ERROR_HANDLER.handleError(e);
        }

Observable.java

        @Override
        public final void onError(Throwable e) {
            throw new OnErrorNotImplementedException(e);
        }

[akarnokd]

Throwing like Observable relies on the expectation that the execution won't switch to other thread. This OnErrorNotImplemented is remnant of the imperative style of programming. Using try-catch around a sequence doesn't make sense and throwing upward has no guarantees either.

[kotucz]

I do not want to wrap the subscribe() call in try-catch. Problem is that when I do not specify onError callback in Completable.subscribe() I do not expect the Completable to emit and error. But when the Completable emits an unexpected error, that is an programming error and shall be processed as such. The OnErrorNotImplementedException is then expected to e.g. crash the application.

Similar to #198 but for Completable

This should be the respective test for Observable:
https://github.com/ReactiveX/RxJava/blob/1.x/src/test/java/rx/ObservableTests.java#L711

[loganj]

@akarnokd Throwing upward does have a crucial guarantee-- reaching the thread's uncaught exception handler.

Delivering to the plugin is effectively swallowing the exception, since it receives all exceptions and cannot safely propagate any of them anywhere.

Failing to propagate exceptions was a huge problem (#1682) in scheduled actions before 1.0.

[akarnokd]

PRs are welcome.

[loganj]

👍 Working on one now. Just going to deliver to the uncaught exception handler after the plugin, wherever it seems to make sense.

[loganj]

@akarnokd Can you explain the usage of toNpe() in Completable, e.g. here?: https://github.com/ReactiveX/RxJava/blob/1.x/src/main/java/rx/Completable.java#L1946

[akarnokd]

You can replace/precede them with Exceptions.throwIfFatal.