ANR in HostnameCache.updateCache while initialising SDK

[vibin]

Integration

sentry-android

Build System

Gradle

AGP Version

7.0.4

Proguard

Enabled

Version

5.7.4

Steps to Reproduce

Initialise the SDK

Expected Result

SDK to initialise without causing any ANR.

Actual Result

ANR is thrown during initialisation.

ANR type: background ANR
OS: Android 10 and 11

main (timed waiting): tid=1 systid=6071 
       at sun.misc.Unsafe.park(Unsafe.java)
       at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:230)
       at java.util.concurrent.FutureTask.awaitDone(FutureTask.java:447)
       at java.util.concurrent.FutureTask.get(FutureTask.java:205)
       at io.sentry.HostnameCache.updateCache(HostnameCache.java:119)
       at io.sentry.HostnameCache.<init>(HostnameCache.java:75)
       at io.sentry.HostnameCache.<init>(HostnameCache.java:62)
       at io.sentry.HostnameCache.<init>(HostnameCache.java:58)
       at io.sentry.HostnameCache.getInstance(HostnameCache.java:52)
       at io.sentry.MainEventProcessor.<init>(MainEventProcessor.java:37)
       at io.sentry.SentryOptions.<init>(SentryOptions.java:1620)
       at io.sentry.SentryOptions.<init>(SentryOptions.java:1600)
       at io.sentry.android.core.SentryAndroidOptions.<init>(SentryAndroidOptions.java:90)
       at java.lang.reflect.Constructor.newInstance0(Constructor.java)
       at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
       at io.sentry.OptionsContainer.createInstance(OptionsContainer.java:24)
       at io.sentry.Sentry.init(Sentry.java:115)
       at io.sentry.android.core.SentryAndroid.init(SentryAndroid.java:83)
       at io.sentry.android.core.SentryAndroid.init(SentryAndroid.java:64)
       at redacted.core.CrashReporter$Companion.initSentry(CrashReporter.kt:96)
       at redacted.core.CrashReporter$Companion.init(CrashReporter.kt:90)
       at redacted.main.initializer.CrashReporterInitializer.initialize(CrashReporterInitializer.kt:12)
       at redacted.main.initializer.AppInitializers.init(AppInitializers.kt:42)
       at redacted.main.RedactedApplication.onCreate(SupplyApplication.java:80)
       at android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1211)
       at android.app.ActivityThread.handleBindApplication(ActivityThread.java:7506)
       at android.app.ActivityThread.access$1600(ActivityThread.java:310)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2281)
       at android.os.Handler.dispatchMessage(Handler.java:106)
       at android.os.Looper.loopOnce(Looper.java:226)
       at android.os.Looper.loop(Looper.java:313)
       at android.app.ActivityThread.main(ActivityThread.java:8663)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:567)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1135)

Sentry init configuration:

SentryAndroid.init(context) { options: SentryAndroidOptions ->
  options.apply {
      release = BuildConfig.VERSION_NAME
      dsn = BuildConfig.SENTRY_DSN
      isEnableNdk = false
      sampleRate = null // Send all errors. No sampling.
      tracesSampleRate = null // Disable tracing.
      tracesSampler = null
      isAnrEnabled = false
      isEnableAutoSessionTracking = true
      sessionTrackingIntervalMillis = redacted
      isSendDefaultPii = false
      addInAppInclude("redacted.android")
      addInAppInclude("redacted.analytics")
      isEnableAppComponentBreadcrumbs = true
      isEnableSystemEventBreadcrumbs = true
      isEnableAppLifecycleBreadcrumbs = true
      isEnableActivityLifecycleBreadcrumbs = false
      addIntegration(SentryActivityFragmentLifecycleIntegration(context)) // Custom integration.
      isEnableAutoActivityLifecycleTracing = false
      isEnableActivityLifecycleTracingAutoFinish = false
      isEnableUserInteractionBreadcrumbs = false
      beforeSend = BeforeSendCallback { event: SentryEvent, hint: Any? ->
          return@BeforeSendCallback if (event.isCrashed) {
              event
          } else {
              null // Swallow non-fatal errors.
          }
      }
  }
}

[philipphofmann]

@vibin, is this happening every time or only under certain conditions?

[vibin]

@philipphofmann According to Crashlytics, this is happening for 0.035% of our DAU. But, Crashlytics only tracks ANRs in Android 10 and 11.

I'm not able to reproduce this issue, so not sure of the conditions (but it's only happening in background, in production)

[philipphofmann]

The problem seems to be here

sentry-java/sentry/src/main/java/io/sentry/HostnameCache.java

Lines 118 to 119 in 9679043

	final Future<Void> futureTask = executorService.submit(hostRetriever);
	futureTask.get(GET_HOSTNAME_TIMEOUT, TimeUnit.MILLISECONDS);

I'm not sure what is causing this. Thanks for reporting this, we need to look into this. I can't give you an ETA at the moment.

[romtsn]

future.get() is indeed a blocking call - but do we even need it @marandaneto? It's gonna always return localhost for an android device anyway (at least from my tests), so perhaps we can just have const here or drop it altogether for Android?

[marandaneto]

This is only read if attachServerName is enabled, Android sets setAttachServerName(false); by default, are you sure its coming from there?
In case the thread is reading and updating the cache on Android, it should not.

[romtsn]

hm, it was definitely hitting the debug breakpoint for me, will re-check

[romtsn]

So it's actually being called, because SentryAndroidOptions ctor calls to SentryAndroid ctor before we setAttachServerName(false) and then it calls all the way to HostnameCache through the MainEventProcessor:

sentry-java/sentry/src/main/java/io/sentry/SentryOptions.java

Line 1709 in 99ade31

eventProcessors.add(new MainEventProcessor(this));

sentry-java/sentry/src/main/java/io/sentry/MainEventProcessor.java

Line 37 in 99ade31

this(options, options.isAttachServerName() ? HostnameCache.getInstance() : null);

what if we lazily initialize HostnameCache when it's actually needed in setServerName here @adinauer ?

sentry-java/sentry/src/main/java/io/sentry/MainEventProcessor.java

Line 167 in 99ade31

if (options.isAttachServerName() && hostnameCache != null && event.getServerName() == null) {

[adinauer]

@romtsn we're also closing the hostnameCache and checking if it's closed in MainEventProcessor so we'd have to keep the hostnameCache field, remove it from ctor and assign it lazily when we need it. If that's what you're suggesting, sounds good to me.

[romtsn]

yeah, we should keep the field 👍

[vibin]

Thanks!

[nienienienie]

@vibin is initializing sentry on main thread, isn't that the root cause of the ANR?

[vibin]

@vibin is initializing sentry on main thread, isn't that the root cause of the ANR?

yes, we're. But initialising sentry on main thread is a valid usecase. The root cause seems to be HostNameCache

[nienienienie]

no really, initializing anything that can take some time, especially from external library which can change without notice, is not valid