SIGSEGV on Android 7

Issue

After updating my application I faced a lot of crashes on android 7 devices. I couldn’t reproduce it on my nexus or on the emulator so I bought one of the crashing devices. After spending half of the day I finally managed to find the root cause and I can reproduce it in a hello world project.

Sample

class MainActivity : Activity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        CoroutineScope(SupervisorJob() + Dispatchers.Main).launch {
            while (true) {
                combine(flowOf(Unit), flowOf(Unit)) { _ -> Unit }.collect()
            }
        }
    }
}

Crash

This leads to a sigsegv

    Flags: 0x28c8bf46
    Package: com.example.weirdcrash v1 (1.0)
    Foreground: Yes
    Build: TCL/5009D/U5A_PLUS_3G:7.0/NRD90M/5009D_ALWE_V2.9_20180529:user/release-keys
    
    *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
    Build fingerprint: 'TCL/5009D/U5A_PLUS_3G:7.0/NRD90M/5009D_ALWE_V2.9_20180529:user/release-keys'
    Revision: '0'
    ABI: 'arm'
    pid: 29639, tid: 29639, name: mple.weirdcrash  >>> com.example.weirdcrash <<<
    signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x15608
        r0 00015000  r1 12d35700  r2 00000002  r3 00000000
        r4 af58a6d8  r5 12d31ee0  r6 12d37280  r7 00000000
        r8 12d35700  r9 ac684400  sl 12cb0a90  fp 12d33bf8
        ip bef2f84c  sp bef2f8b0  lr 9901f5ef  pc 9901f608  cpsr 000f0030
    
    backtrace:
        #00 pc 00000608  /dev/ashmem/dalvik-jit-code-cache (deleted)
        #01 pc 000005ed  /dev/ashmem/dalvik-jit-code-cache (deleted)
     29639

I currently see about 1200 affected users…

Versions

'com.android.tools.build:gradle:3.6.0-beta04'
"org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.2"
"org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.2"

Affected Devices

Note

Take a look at the last crash, maybe that’s an indicator for what’s going wrong. That one is no native crash but an android 7 only issue.

[PaulWoitaschek]

I have written a non-rx version:

/**
 * Because of a bug in android 7 we can't use the regular combine functions and have to use our own.
 * @see [https://github.com/Kotlin/kotlinx.coroutines/issues/1683]
 */
@PublishedApi
internal object UnInitialized

@PublishedApi
internal inline fun <T, R> combine(vararg sources: Flow<T>, crossinline transform: suspend (List<T>) -> R): Flow<R> {
  return channelFlow {
    val values = Array<Any?>(sources.size) { UnInitialized }
    coroutineScope {
      sources.forEachIndexed { index, flow ->
        launch {
          flow.collect { value ->
            values[index] = value
            if (values.all { it !== UnInitialized }) {
              @Suppress("UNCHECKED_CAST")
              send(transform(values.toList() as List<T>))
            }
          }
        }
      }
    }
  }
}

[qwwdfsad]

@mhernand40 Unfortunately, we do not know. The stable reproducer is required in order to check such a hypothesis