perf(core): Remove executor prewarm

SentryExecutorService is single-threaded, and prewarm() is submitted ahead
of loadLazyFields() during init, so its 40-task schedule/cancel/purge loop
cannot reduce first-task latency — it can only delay it. The thread creation
and executor class loading it aimed to warm are paid identically by the first
real task (loadLazyFields), which is submitted unconditionally right after,
so prewarm warms nothing that would not already be warmed.

On-device A/B benchmarks on a Galaxy A55 (Android 16) show no measurable
first-useful-task speedup from prewarm and ~20us of extra background-thread
work. Remove prewarm() from ISentryExecutorService and its implementations
and from both init call sites.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: runningcode

CHANGELOG.md

@@ -17,6 +17,8 @@
 
 - Skip `Hint` allocation in `Scope.addBreadcrumb` when no `beforeBreadcrumb` callback is set ([#5689](https://github.com/getsentry/sentry-java/pull/5689))
 - Speed up scope persistence by detecting the Sentry executor thread via a marker instead of a `Thread.getName()` name scan on every scope mutation ([#5691](https://github.com/getsentry/sentry-java/pull/5691))
+- Remove executor prewarm during SDK init ([#5681](https://github.com/getsentry/sentry-java/pull/5681))
+  - The single-threaded `SentryExecutorService` queued the prewarm work ahead of the first useful task, so it could only delay init work, never speed it up; the thread and class loading it warmed are paid identically by the first real task submitted right after.
 
 ## 8.47.0
 

sentry-android-core/src/test/java/io/sentry/android/core/AndroidProfilerTest.kt

@@ -81,8 +81,6 @@ class AndroidProfilerTest {
         override fun close(timeoutMillis: Long) {}
 
         override fun isClosed() = false
-
-        override fun prewarm() = Unit
       }
 
     val options =

sentry-android-core/src/test/java/io/sentry/android/core/AndroidTransactionProfilerTest.kt

@@ -89,8 +89,6 @@ class AndroidTransactionProfilerTest {
         override fun close(timeoutMillis: Long) {}
 
         override fun isClosed() = false
-
-        override fun prewarm() = Unit
       }
 
     val options =

sentry-test-support/src/main/kotlin/io/sentry/test/Mocks.kt

@@ -35,8 +35,6 @@ class ImmediateExecutorService : ISentryExecutorService {
   override fun close(timeoutMillis: Long) {}
 
   override fun isClosed(): Boolean = false
-
-  override fun prewarm() = Unit
 }
 
 class DeferredExecutorService : ISentryExecutorService {
@@ -74,8 +72,6 @@ class DeferredExecutorService : ISentryExecutorService {
 
   override fun isClosed(): Boolean = false
 
-  override fun prewarm() = Unit
-
   fun hasScheduledRunnables(): Boolean = scheduledRunnables.isNotEmpty()
 }
 
@@ -90,8 +86,6 @@ class NonOverridableNoOpSentryExecutorService : ISentryExecutorService {
   override fun close(timeoutMillis: Long) {}
 
   override fun isClosed(): Boolean = false
-
-  override fun prewarm() = Unit
 }
 
 fun createSentryClientMock(enabled: Boolean = true) =

sentry/api/sentry.api

@@ -1134,7 +1134,6 @@ public abstract interface class io/sentry/ISentryClient {
 public abstract interface class io/sentry/ISentryExecutorService {
 	public abstract fun close (J)V
 	public abstract fun isClosed ()Z
-	public abstract fun prewarm ()V
 	public abstract fun schedule (Ljava/lang/Runnable;J)Ljava/util/concurrent/Future;
 	public abstract fun submit (Ljava/lang/Runnable;)Ljava/util/concurrent/Future;
 	public abstract fun submit (Ljava/util/concurrent/Callable;)Ljava/util/concurrent/Future;
@@ -1880,7 +1879,6 @@ public final class io/sentry/NoOpSentryExecutorService : io/sentry/ISentryExecut
 	public fun close (J)V
 	public static fun getInstance ()Lio/sentry/ISentryExecutorService;
 	public fun isClosed ()Z
-	public fun prewarm ()V
 	public fun schedule (Ljava/lang/Runnable;J)Ljava/util/concurrent/Future;
 	public fun submit (Ljava/lang/Runnable;)Ljava/util/concurrent/Future;
 	public fun submit (Ljava/util/concurrent/Callable;)Ljava/util/concurrent/Future;
@@ -3183,7 +3181,6 @@ public final class io/sentry/SentryExecutorService : io/sentry/ISentryExecutorSe
 	public fun close (J)V
 	public fun isClosed ()Z
 	public static fun isSentryExecutorThread ()Z
-	public fun prewarm ()V
 	public fun schedule (Ljava/lang/Runnable;J)Ljava/util/concurrent/Future;
 	public fun submit (Ljava/lang/Runnable;)Ljava/util/concurrent/Future;
 	public fun submit (Ljava/util/concurrent/Callable;)Ljava/util/concurrent/Future;

sentry/src/main/java/io/sentry/ISentryExecutorService.java

@@ -45,10 +45,4 @@ Future<?> schedule(final @NotNull Runnable runnable, final long delayMillis)
    * @return If the executorService was previously closed
    */
   boolean isClosed();
-
-  /**
-   * Pre-warms the executor service by increasing the initial queue capacity. SHOULD be called
-   * directly after instantiating this executor service.
-   */
-  void prewarm();
 }

sentry/src/main/java/io/sentry/NoOpSentryExecutorService.java

@@ -38,7 +38,4 @@ public void close(long timeoutMillis) {}
   public boolean isClosed() {
     return false;
   }
-
-  @Override
-  public void prewarm() {}
 }

sentry/src/main/java/io/sentry/Sentry.java

@@ -351,7 +351,6 @@ private static void init(final @NotNull SentryOptions options, final boolean glo
         // to set a new one
         if (options.getExecutorService().isClosed()) {
           options.setExecutorService(new SentryExecutorService(options));
-          options.getExecutorService().prewarm();
         }
 
         // load lazy fields of the options in a separate thread

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

@@ -16,13 +16,6 @@
 @ApiStatus.Internal
 public final class SentryExecutorService implements ISentryExecutorService {
 
-  /**
-   * ScheduledThreadPoolExecutor grows work queue by 50% each time. With the initial capacity of 16
-   * it will have to resize 4 times to reach 40, which is a decent middle-ground for prewarming.
-   * This will prevent from growing in unexpected areas of the SDK.
-   */
-  private static final int INITIAL_QUEUE_SIZE = 40;
-
   /**
    * By default, the work queue is unbounded so it can grow as much as the memory allows. We want to
    * limit it by 271 which would be x8 times growth from the default initial capacity.
@@ -32,9 +25,6 @@ public final class SentryExecutorService implements ISentryExecutorService {
   private final @NotNull ScheduledThreadPoolExecutor executorService;
   private final @NotNull AutoClosableReentrantLock lock = new AutoClosableReentrantLock();
 
-  @SuppressWarnings("UnnecessaryLambda")
-  private final @NotNull Runnable dummyRunnable = () -> {};
-
   private final @Nullable SentryOptions options;
 
   @TestOnly
@@ -120,35 +110,6 @@ public boolean isClosed() {
     }
   }
 
-  @SuppressWarnings({"FutureReturnValueIgnored"})
-  @Override
-  public void prewarm() {
-    try {
-      executorService.submit(
-          () -> {
-            try {
-              // schedule a bunch of dummy runnables in the future that will never execute to
-              // trigger
-              // queue growth and then purge the queue
-              for (int i = 0; i < INITIAL_QUEUE_SIZE; i++) {
-                final Future<?> future =
-                    executorService.schedule(dummyRunnable, 365L, TimeUnit.DAYS);
-                future.cancel(true);
-              }
-              executorService.purge();
-            } catch (RejectedExecutionException ignored) {
-              // ignore
-            }
-          });
-    } catch (RejectedExecutionException e) {
-      if (options != null) {
-        options
-            .getLogger()
-            .log(SentryLevel.WARNING, "Prewarm task rejected from " + executorService, e);
-      }
-    }
-  }
-
   /**
    * Whether the calling thread is one of the Sentry executor threads. Cheap replacement for
    * scanning {@code Thread.currentThread().getName()}, which is on hot paths (e.g. scope

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

@@ -678,7 +678,6 @@ public void activate() {
       // SentryExecutorService should be initialized before any
       // SendCachedEventFireAndForgetIntegration
       executorService = new SentryExecutorService(this);
-      executorService.prewarm();
     }
 
     // SpotlightIntegration is loaded via reflection to allow the sentry-spotlight module