perf: Drop pending timer tasks on shutdown to unblock close (JAVA-653)

CHANGELOG.md

@@ -15,6 +15,7 @@
 ### Performance
 
 - Reduce the number of SDK threads: `LifecycleWatcher` now schedules the session-end task on the shared timer executor instead of creating a dedicated `java.util.Timer` thread ([#5819](https://github.com/getsentry/sentry-java/pull/5819))
+- Avoid waiting up to `shutdownTimeoutMillis` when closing the SDK with a pending transaction timeout or session-end task ([#5851](https://github.com/getsentry/sentry-java/pull/5851))
 - Speed up deserialization of arbitrary JSON objects by typing numbers without throwing exceptions ([#5783](https://github.com/getsentry/sentry-java/pull/5783))
 
 ### Dependencies

sentry/src/main/java/io/sentry/SentryExecutorService.java

@@ -56,6 +56,10 @@ public SentryExecutorService(final @Nullable SentryOptions options) {
     executorService.setRemoveOnCancelPolicy(removeOnCancelPolicy);
     executorService.setKeepAliveTime(keepAliveTime, keepAliveTimeUnit);
     executorService.allowCoreThreadTimeOut(true);
+    // by default shutdown() keeps queued delayed tasks, so awaitTermination blocks for the full
+    // shutdown timeout whenever a long timeout is still pending. Those tasks are discarded by the
+    // subsequent shutdownNow() anyway, so dropping them upfront only saves the wait.
+    executorService.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
   }
 
   public SentryExecutorService() {

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

@@ -8,6 +8,7 @@ import java.util.concurrent.LinkedBlockingQueue
 import java.util.concurrent.ScheduledThreadPoolExecutor
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.atomic.AtomicBoolean
+import kotlin.system.measureTimeMillis
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
@@ -110,6 +111,27 @@ class SentryExecutorServiceTest {
     sentryExecutor.close(15000)
   }
 
+  @Test
+  fun `SentryExecutorService discards pending delayed tasks on shutdown when requested`() {
+    val sentryExecutor = SentryExecutorService(null, true, 30, TimeUnit.SECONDS)
+    val executor = sentryExecutor.getProperty<ScheduledThreadPoolExecutor>("executorService")
+    assertFalse(executor.executeExistingDelayedTasksAfterShutdownPolicy)
+    sentryExecutor.close(15000)
+  }
+
+  @Test
+  fun `SentryExecutorService close does not wait for a pending delayed task`() {
+    val sentryExecutor = SentryExecutorService(null, true, 30, TimeUnit.SECONDS)
+    val ran = AtomicBoolean(false)
+    sentryExecutor.schedule({ ran.set(true) }, 30000)
+
+    val elapsed = measureTimeMillis { sentryExecutor.close(5000) }
+
+    assertTrue(elapsed < 5000, "close blocked for ${elapsed}ms waiting on the pending task")
+    assertTrue(sentryExecutor.isClosed)
+    assertFalse(ran.get())
+  }
+
   @Test
   fun `SentryExecutorService isClosed returns true if executor is shutdown`() {
     val executor = mock<ScheduledThreadPoolExecutor>()