call a suspend function inside a normal function

Question

I want to call blocking a suspend function in a normal function, but does not block Thread to finishing suspend function and then return Response

override fun intercept(chain: Interceptor.Chain): Response { // getSession is a suspend function val session = sessionProvider.getSession() return chain.proceed( chain .request() .newBuilder() .addHeader("Authorization", "${session.token}") .build() ) }

You need to block the thread if you want to return value from your function. If you don't want to block you need to use callback function. — Pawel
– Pawel, Commented Jun 1, 2019 at 19:56

CommonsWare · Accepted Answer · 2019-06-01 19:56:57Z

72

This looks like you are implementing an OkHttp interceptor, so I am hoping that intercept() is being called on a background thread.

If so, use runBlocking():

override fun intercept(chain: Interceptor.Chain): Response { // getSession is a suspend function val session = runBlocking { sessionProvider.getSession() } return chain.proceed( chain .request() .newBuilder() .addHeader("Authorization", "${session.token}") .build() ) }

runBlocking() will execute the suspend function, blocking the current thread until that work is complete.

answered Jun 1, 2019 at 19:56

CommonsWare

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10 Comments

3366784 Over a year ago

Would this cause issues because the return will be delayed and the intercept function is not marked as a suspend function?

CommonsWare Over a year ago

@3366784: runBlocking() is not itself an suspend function, so from a compilation standpoint, everything should be fine. How well this works at runtime depends a lot on how well-behaved sessionProvider.getSession() is. If that takes a long time, every OkHttp request will take a long time, because the runBlocking() call is a blocking call, and intercept() will not proceed until runBlocking() completes.

3366784 Over a year ago

Okay I understand it depends on .getSession(). I was confused because I know there are some languages that will kill your app if a regular function with return value take more than x seconds to return. But in this situation we are forced to delay the return and as you said this is okay. I tested this and added an extra delay and it didn't block the UI thread and didn't crash therefore it should be good.

The incredible Jan Over a year ago

@3366784 "languages that will kill your app if a regular function with return value take more than x seconds to return" - could you provide examples? I've never heard of that kind of language feature.

user924 Over a year ago

yeah Retrofit by default should run suspend api methods on its predefined background io dispatcher

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