fix(core): Keep resolving the hostname after Sentry.close() (#6119)

* fix(core): Keep resolving the hostname after Sentry.close()

MainEventProcessor was Closeable, so Scopes.close() closed it, and it shut
down the process-wide HostnameCache singleton. Nothing ever replaced that
singleton: INSTANCE is assigned once and never cleared, so a re-init handed the
same shut-down cache to the new MainEventProcessor, and to MetricsApi and
LoggerApi, which read it directly.

The damage was silent and permanent. While the cache was still fresh,
getHostname() kept returning the value it already had. On the first expiry
after the close, getHostname() flipped updateRunning to true and then
submit() threw RejectedExecutionException on the terminated executor. That is
a RuntimeException, so it was swallowed into handleCacheUpdateFailure(), but
the updateRunning reset lives in the submitted callable's finally block, which
never ran. updateRunning stayed true, so the compareAndSet guard failed from
then on and no refresh was ever attempted again. server_name froze at its last
resolved value for the life of the process, with no exception and no log line.

Nothing needs to close this cache. Its executor is a single daemon thread with
allowCoreThreadTimeOut(true) and a 30 second keep-alive, so the worker exits on
its own once idle and never holds up process exit; the thread exists for about
30 seconds out of every 5 hour refresh interval. Scopes.close() already leaves
the timer executor running for exactly this reason.

The one test that covered this path, SentryClientTest's `when client is closed,
hostname cache is closed`, asserted isClosed() on a processor that had never
resolved a hostname, where isClosed() returned true because the cache was still
null. It never exercised the behavior it named. Replaced with an assertion that
MainEventProcessor is not Closeable, which fails if the wiring comes back.

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

* changelog

* fix(core): Clear updateRunning when a refresh cannot be queued

updateRunning is cleared in exactly one place, the submitted callable's finally
block, so it is cleared if and only if the callable runs. Every failure from
Future.get() leaves the callable running, so it still clears the flag itself.
A failure from submit() does not: the callable was never queued, nothing clears
the flag, and the compareAndSet guard in getHostname() then fails forever, so
no refresh is ever attempted again.

Removing MainEventProcessor's close() took away the only reachable way to make
submit() throw, but the invariant was still wrong: a bounded queue, a shutdown
added later, or a failure to start a thread would silently resurrect the same
permanent freeze.

Splitting submit() out of the try means the two cases can be told apart.
Clearing the flag on a timeout or an interrupt as well would be wrong, since
the callable is still running there and refreshes would pile up behind a slow
lookup; MainEventProcessorTest's `sets servername to null if retrieving takes
longer time` covers that path.

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

* test(core): Drop the not-Closeable assertion

It asserted a type relationship rather than behavior, which says nothing about
whether the hostname keeps resolving. The behavior that matters is covered by
HostnameCacheTest: `worker thread times out while idle instead of staying
alive` guards the self-terminating executor that makes closing unnecessary, and
`a refresh that cannot be queued does not stop later refreshes` guards the
latch that turned a one-off failure into a permanent one.

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

---------

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

Author: runningcode

CHANGELOG.md

@@ -35,6 +35,10 @@
 - Sentry can now configure Log4j2 automatically for Spring Boot 3 when `sentry-log4j2` is on the classpath and Log4j2 Core is the active logging backend ([#6072](https://github.com/getsentry/sentry-java/pull/6072))
   - Disabled by default for now; enable it and configure levels the same way as described in the Spring Boot 4 entry above (`sentry.logging.enabled=true`)
 
+### Fixes
+
+- Keep resolving the server name after `Sentry.close()` or a re-init. Closing the SDK shut down the shared hostname cache for the life of the process, so `server_name` silently froze at the value it had last resolved ([#6119](https://github.com/getsentry/sentry-java/pull/6119))
+
 ### Internal
 
 - Deprecate `AndroidCurrentDateProvider.getInstance()` in favor of `MonotonicTicker`, which counts time spent in deep sleep and cannot be confused with the epoch-based `CurrentDateProvider` ([#6103](https://github.com/getsentry/sentry-java/pull/6103))

sentry/api/sentry.api

@@ -1392,9 +1392,8 @@ public abstract interface class io/sentry/JsonUnknown {
 	public abstract fun setUnknown (Ljava/util/Map;)V
 }
 
-public final class io/sentry/MainEventProcessor : io/sentry/EventProcessor, java/io/Closeable {
+public final class io/sentry/MainEventProcessor : io/sentry/EventProcessor {
 	public fun <init> (Lio/sentry/SentryOptions;)V
-	public fun close ()V
 	public fun getOrder ()Ljava/lang/Long;
 	public fun process (Lio/sentry/SentryEvent;Lio/sentry/Hint;)Lio/sentry/SentryEvent;
 	public fun process (Lio/sentry/SentryLogEvent;)Lio/sentry/SentryLogEvent;

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

@@ -8,6 +8,7 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
@@ -91,7 +92,7 @@ private HostnameCache() {
     this.cacheDuration = cacheDuration;
     this.getLocalhost = Objects.requireNonNull(getLocalhost, "getLocalhost is required");
     // A single thread executor whose worker thread times out while idle, so no thread is kept
-    // alive between the infrequent cache refreshes.
+    // alive between the infrequent cache refreshes and nothing has to shut it down.
     final @NotNull ThreadPoolExecutor executor =
         new ThreadPoolExecutor(
             1,
@@ -105,14 +106,6 @@ private HostnameCache() {
     updateCache();
   }
 
-  void close() {
-    this.executorService.shutdown();
-  }
-
-  boolean isClosed() {
-    return this.executorService.isShutdown();
-  }
-
   /**
    * Gets the hostname of the current machine.
    *
@@ -144,8 +137,21 @@ private void updateCache() {
           return null;
         };
 
+    final Future<Void> futureTask;
+    try {
+      futureTask = executorService.submit(hostRetriever);
+    } catch (RejectedExecutionException e) {
+      // updateRunning is cleared by the callable's finally block, which never runs if the callable
+      // was never queued. Clearing it here keeps a failure to queue from latching the flag on and
+      // silencing every later refresh.
+      updateRunning.set(false);
+      handleCacheUpdateFailure();
+      return;
+    }
+
+    // A timeout or interrupt below leaves the callable running, so it still clears updateRunning
+    // itself; doing it here as well would let refreshes pile up behind a slow lookup.
     try {
-      final Future<Void> futureTask = executorService.submit(hostRetriever);
       futureTask.get(GET_HOSTNAME_TIMEOUT, TimeUnit.MILLISECONDS);
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();

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

@@ -8,18 +8,15 @@
 import io.sentry.protocol.SentryTransaction;
 import io.sentry.protocol.User;
 import io.sentry.util.HintUtils;
-import java.io.Closeable;
-import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
-import org.jetbrains.annotations.VisibleForTesting;
 
 @ApiStatus.Internal
-public final class MainEventProcessor implements EventProcessor, Closeable {
+public final class MainEventProcessor implements EventProcessor {
 
   private final @NotNull SentryOptions options;
   private final @NotNull SentryThreadFactory sentryThreadFactory;
@@ -271,27 +268,6 @@ private boolean isCachedHint(final @NotNull Hint hint) {
     return HintUtils.hasType(hint, Cached.class);
   }
 
-  @Override
-  public void close() throws IOException {
-    if (hostnameCache != null) {
-      hostnameCache.close();
-    }
-  }
-
-  boolean isClosed() {
-    if (hostnameCache != null) {
-      return hostnameCache.isClosed();
-    } else {
-      return true;
-    }
-  }
-
-  @VisibleForTesting
-  @Nullable
-  HostnameCache getHostnameCache() {
-    return hostnameCache;
-  }
-
   @Override
   public @Nullable Long getOrder() {
     return 0L;

sentry/src/test/java/io/sentry/HostnameCacheTest.kt

@@ -2,9 +2,11 @@ package io.sentry
 
 import com.google.common.truth.Truth.assertThat
 import io.sentry.test.getProperty
+import io.sentry.test.injectForField
 import java.net.InetAddress
 import java.util.concurrent.ThreadPoolExecutor
 import java.util.concurrent.TimeUnit
+import java.util.concurrent.atomic.AtomicBoolean
 import kotlin.test.Test
 import org.mockito.kotlin.mock
 import org.mockito.kotlin.whenever
@@ -23,6 +25,21 @@ class HostnameCacheTest {
     assertThat(cache.hostname).isEqualTo("myhost")
   }
 
+  @Test
+  fun `a refresh that cannot be queued does not stop later refreshes`() {
+    val cache = getSut()
+    // Reject the next submit the way an executor that could not start a thread would, and mark the
+    // cache stale so that reading the hostname attempts a refresh.
+    cache.getProperty<ThreadPoolExecutor>("executorService").shutdown()
+    cache.injectForField("expirationTimestamp", 0L)
+
+    assertThat(cache.hostname).isEqualTo("myhost")
+
+    // The callable never ran, so nothing else clears this flag; left set, it would fail the
+    // compareAndSet guard in getHostname() and no refresh would ever be attempted again.
+    assertThat(cache.getProperty<AtomicBoolean>("updateRunning").get()).isFalse()
+  }
+
   @Test
   fun `worker thread times out while idle instead of staying alive`() {
     val cache = getSut()
@@ -31,11 +48,4 @@ class HostnameCacheTest {
     assertThat(executorService.corePoolSize).isEqualTo(1)
     assertThat(executorService.maximumPoolSize).isEqualTo(1)
   }
-
-  @Test
-  fun `close shuts the executor down`() {
-    val cache = getSut()
-    cache.close()
-    assertThat(cache.isClosed).isTrue()
-  }
 }

sentry/src/test/java/io/sentry/MainEventProcessorTest.kt

@@ -571,16 +571,6 @@ class MainEventProcessorTest {
     }
   }
 
-  @Test
-  fun `when processor is closed, closes hostname cache`() {
-    val sut = fixture.getSut(serverName = null)
-
-    sut.process(SentryTransaction(fixture.sentryTracer), Hint())
-
-    sut.close()
-    assertNotNull(sut.hostnameCache) { assertTrue(it.isClosed) }
-  }
-
   @Test
   fun `when event has modules, appends to them`() {
     val sut = fixture.getSut(modules = mapOf("group1:artifact1" to "2.0.0"))

sentry/src/test/java/io/sentry/SentryClientTest.kt

@@ -214,16 +214,6 @@ class SentryClientTest {
     assertFalse(sut.isEnabled)
   }
 
-  @Test
-  fun `when client is closed, hostname cache is closed`() {
-    val sut = fixture.getSut()
-    assertTrue(sut.isEnabled)
-    sut.close()
-    val mainEventProcessor =
-      fixture.sentryOptions.eventProcessors.filterIsInstance<MainEventProcessor>().first()
-    assertTrue(mainEventProcessor.isClosed)
-  }
-
   @Test
   fun `when beforeSend is set, callback is invoked`() {
     var invoked = false