ref(android): Require an installed ticker for ANR profiling (JAVA-579)

Drop the JavaMonotonicTicker fallback. On Android nanoTime() stops while the
device is suspended, so a default that is never meant to be used would measure
main-thread stalls against the wrong clock if it ever were.

Start the test ticker at a non-zero origin. A fake that starts at zero makes a
reading taken against a different origin indistinguishable from a correct one,
which is the mistake this whole change exists to prevent.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: runningcode

sentry-android-core/src/main/java/io/sentry/android/core/anr/AnrProfilingIntegration.java

@@ -13,7 +13,6 @@
 import io.sentry.SentryOptions;
 import io.sentry.android.core.AppState;
 import io.sentry.android.core.SentryAndroidOptions;
-import io.sentry.time.JavaMonotonicTicker;
 import io.sentry.time.MonotonicTicker;
 import io.sentry.time.MonotonicTickerProvider;
 import io.sentry.time.Stopwatch;
@@ -47,10 +46,22 @@ public class AnrProfilingIntegration
   static final int MAX_NUM_STACKS = (int) (10_000 / POLLING_INTERVAL_MS);
 
   private final AtomicBoolean enabled = new AtomicBoolean(true);
-  private volatile @NotNull MonotonicTicker ticker = JavaMonotonicTicker.getInstance();
+
+  /**
+   * Null until {@link #register} installs one. There is deliberately no default: the core module's
+   * ticker reads {@link System#nanoTime()}, which stops while the device is suspended, so falling
+   * back to it on Android would silently measure stalls against the wrong clock.
+   */
+  private volatile @Nullable MonotonicTicker ticker;
 
   @SuppressWarnings("UnnecessaryLambda")
-  private final @NotNull Runnable updater = () -> lastMainThreadExecutionNanos = ticker.tickNanos();
+  private final @NotNull Runnable updater =
+      () -> {
+        final @Nullable MonotonicTicker currentTicker = ticker;
+        if (currentTicker != null) {
+          lastMainThreadExecutionNanos = currentTicker.tickNanos();
+        }
+      };
 
   private final @NotNull AutoClosableReentrantLock lifecycleLock = new AutoClosableReentrantLock();
   private final @NotNull AutoClosableReentrantLock profileManagerLock =
@@ -76,8 +87,9 @@ public class AnrProfilingIntegration
    * SentryAndroidOptions} cannot supply.
    */
   void installTickerFrom(final @NotNull MonotonicTickerProvider provider) {
-    this.ticker = provider.getMonotonicTicker();
-    this.lastMainThreadExecutionNanos = ticker.tickNanos();
+    final @NotNull MonotonicTicker installedTicker = provider.getMonotonicTicker();
+    this.ticker = installedTicker;
+    this.lastMainThreadExecutionNanos = installedTicker.tickNanos();
   }
 
   @Override
@@ -232,8 +244,12 @@ public void run() {
 
   @ApiStatus.Internal
   protected void checkMainThread(final @NotNull Thread mainThread) throws IOException {
+    final @Nullable MonotonicTicker currentTicker = ticker;
+    if (currentTicker == null) {
+      return;
+    }
     final long diff =
-        TimeUnit.NANOSECONDS.toMillis(ticker.tickNanos() - lastMainThreadExecutionNanos);
+        TimeUnit.NANOSECONDS.toMillis(currentTicker.tickNanos() - lastMainThreadExecutionNanos);
 
     if (diff < THRESHOLD_SUSPICION_MS) {
       mainThreadState = MainThreadState.IDLE;
@@ -262,7 +278,7 @@ protected void checkMainThread(final @NotNull Thread mainThread) throws IOExcept
         && (mainThreadState == MainThreadState.SUSPICIOUS
             || mainThreadState == MainThreadState.ANR_DETECTED)) {
       if (numCollectedStacks.get() < MAX_NUM_STACKS) {
-        final @NotNull Stopwatch stopwatch = Stopwatch.started(ticker);
+        final @NotNull Stopwatch stopwatch = Stopwatch.started(currentTicker);
         final @NotNull AnrStackTrace trace =
             new AnrStackTrace(System.currentTimeMillis(), mainThread.getStackTrace());
         if (logger.isEnabled(SentryLevel.DEBUG)) {

sentry-android-core/src/test/java/io/sentry/android/core/anr/AnrProfilingIntegrationTest.kt

@@ -1,6 +1,7 @@
 package io.sentry.android.core.anr
 
 import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
 import io.sentry.ILogger
 import io.sentry.IScopes
 import io.sentry.SentryIntegrationPackageStorage
@@ -9,6 +10,7 @@ import io.sentry.android.core.AppState
 import io.sentry.android.core.SentryAndroidOptions
 import io.sentry.test.getProperty
 import io.sentry.time.TestMonotonicTicker
+import java.util.concurrent.TimeUnit.HOURS
 import java.util.concurrent.TimeUnit.MILLISECONDS
 import kotlin.test.AfterTest
 import kotlin.test.BeforeTest
@@ -35,7 +37,9 @@ class AnrProfilingIntegrationTest {
 
   @BeforeTest
   fun setup() {
-    ticker = TestMonotonicTicker()
+    // A tick origin far from zero, as on any device that has been up a while. Starting at zero
+    // would let a reading taken against a different origin pass unnoticed.
+    ticker = TestMonotonicTicker(HOURS.toNanos(30))
     mockScopes = mock()
     mockLogger = mock()
     options =
@@ -223,6 +227,18 @@ class AnrProfilingIntegrationTest {
     assertEquals(AnrProfilingIntegration.MainThreadState.IDLE, integration.state)
   }
 
+  @Test
+  fun `does not report a stall when the ticker origin is far from zero`() {
+    val integration = AnrProfilingIntegration()
+    integration.register(mockScopes, options)
+    integration.installTickerFrom { ticker }
+
+    integration.checkMainThread(Thread.currentThread())
+
+    assertThat(integration.state).isEqualTo(AnrProfilingIntegration.MainThreadState.IDLE)
+    assertThat(integration.profileManager.load().stacks).isEmpty()
+  }
+
   @Test
   fun `does not register when options is not SentryAndroidOptions`() {
     val plainOptions =