Netty: StrictMode Violations on Android Due to Non-SDK API Usage

[Igor Khrupin]

Hi Netty Team,

We’re encountering two StrictMode violations on Android when using Netty, both related to usage of non-SDK interfaces. These occur with StrictMode.VmPolicy.Builder().detectNonSdkApiUsage() enabled on Android 9 and above.
Reference: StrictMode Documentation

Environment:

• Netty version: 4.1.72 (also reproduced on 4.1.99)

• Android version: 10+

• Use case: MQTT client via HiveMQ (which uses Netty internally)

---

Violation 1: sun.misc.VM.maxDirectMemory()

StrictMode policy violation: android.os.strictmode.NonSdkApiUsedViolation: Lsun/misc/VM;->maxDirectMemory()J  
  at android.os.StrictMode.lambda$static$1(StrictMode.java:430)  
  at java.lang.Class.getDeclaredMethodInternal(Native Method)  
  at io.netty.util.internal.PlatformDependent.maxDirectMemory0(PlatformDependent.java:1097)  
  ...

• Module: common

• Class: PlatformDependent

• Method: maxDirectMemory0()

Violation 2: SelectorImpl.selectedKeys

StrictMode policy violation: android.os.strictmode.NonSdkApiUsedViolation: Lsun/nio/ch/SelectorImpl;->selectedKeys:Ljava/util/Set;  
  at android.os.StrictMode.lambda$static$1(StrictMode.java:430)  
  at java.lang.Class.getDeclaredField(Native Method)  
  at io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:209)  
  ...

• Module: transport

• Class: NioEventLoop

Reproduction Steps:

1. Integrate Netty into an Android application

2. Enable this StrictMode config on Android 9+:

   if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
       StrictMode.setVmPolicy(
           new StrictMode.VmPolicy.Builder()
               .detectNonSdkApiUsage()
               .penaltyLog()
               .build()
       );
   }
   

3. Run the app on a device or emulator

4. Observe the violations in Logcat

---

Request:
Could you advise whether these internal API usages can be eliminated or optionally isolated behind a configurable flag?

We appreciate your work and contributions to the Netty project — thank you!

Best regards,

--

Igor Khrupin

Senior Software Engineer II | Life360 Inc.

1900 S Norfolk St #310,
San Mateo, CA 94403

Check out our open positions: life360.com/careers