尽管使用RxJava订阅了另一个线程，但在使用Google的People API时仍会收到IllegalStateException

Question

Note: I'm using Kotlin along with RxKotlin for the useful extension functions.

I'm trying to get some user data using Google's People API, and I just migrated all my AsyncTasks and stuff to using RxJava. Everything is working except for this part:

private fun getGooglePerson(service: PeopleService?, account: GoogleSignInAccount) =
    Single.just(service?.people()
                    ?.get("people/me")
                    ?.setPersonFields("emailAddresses,birthdays,genders,phoneNumbers")
                    ?.execute() ?: Person()) // If null, return an empty person (shouldn't ever be null, though)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeBy(
                    onError = {/*Do something*/},
                    onSuccess = {/*Do something*/}
            )

Specifically, I'm getting an IllegalStateException with the message, Calling this from your main thread can lead to deadlock . I'm confused because I was under the impression that calling subscribeOn should shift everything both above and below it (unless an observeOn follows it) to another thread (in this case, Schedulers.io() ) I tried rewriting the code like so:

private fun getGooglePerson(service: PeopleService?, account: GoogleSignInAccount) =
    service?.people()
                    ?.get("people/me")
                    ?.setPersonFields("emailAddresses,birthdays,genders,phoneNumbers")
                    ?.execute() ?: Person() // If null, return an empty person (shouldn't ever be null, though)
            .toSingle()
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeBy(
                    onError = {/*Do something*/},
                    onSuccess = {/*Do something*/}
            )

Still, no dice. I'm completely stumped; what should I do? Where should I put that call to execute() so that it runs on a different thread? Am I missing something?

Answer 1

Let's break this down a little.

Single.just(service?.people()
                    ?.get("people/me")
                    ?.setPersonFields("emailAddresses,birthdays,genders,phoneNumbers")
                    ?.execute() ?: Person())
            .subscribeOn(Schedulers.io())

We're starting with a Single.just(someValue) . We could rewrite your code like so, and it would be technically identical to what you wrote:

val person = service?.people()
                    ?.get("people/me")
                    ?.setPersonFields("emailAddresses,birthdays,genders,phoneNumbers")
                    ?.execute() ?: Person())
Single.just(person)

Do you see the problem? The service call is executed first in order to provide a value to the Single.just call.

In order to run your service call once the rest of the chain has been setup (ie, upon subscription), you can use defer :

Single.defer(() -> service?.people()
                    ?.get("people/me")
                    ?.setPersonFields("emailAddresses,birthdays,genders,phoneNumbers")
                    ?.execute() ?: Person())
            .subscribeOn(Schedulers.io())

(syntax may be off, I don't have an IDE handy)