Use daemon threads for SentryExecutorService (#2747)

Author: adinauer

CHANGELOG.md

@@ -12,9 +12,8 @@
 ### Fixes
 
 - Finish WebFlux transaction before popping scope ([#2724](https://github.com/getsentry/sentry-java/pull/2724))
-
-### Fixes
-
+- Use daemon threads for SentryExecutorService ([#2747](https://github.com/getsentry/sentry-java/pull/2747))
+  - We started using `SentryExecutorService` in `6.19.0` which caused the application to hang on shutdown unless `Sentry.close()` was called. By using daemon threads we no longer block shutdown.
 - Use Base64.NO_WRAP to avoid unexpected char errors in Apollo ([#2745](https://github.com/getsentry/sentry-java/pull/2745))
 - Don't warn R8 on missing `ComposeViewHierarchyExporter` class ([#2743](https://github.com/getsentry/sentry-java/pull/2743))
 

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

@@ -4,6 +4,7 @@
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.TestOnly;
@@ -18,7 +19,7 @@ final class SentryExecutorService implements ISentryExecutorService {
   }
 
   SentryExecutorService() {
-    this(Executors.newSingleThreadScheduledExecutor());
+    this(Executors.newSingleThreadScheduledExecutor(new SentryExecutorServiceThreadFactory()));
   }
 
   @Override
@@ -59,4 +60,15 @@ public boolean isClosed() {
       return executorService.isShutdown();
     }
   }
+
+  private static final class SentryExecutorServiceThreadFactory implements ThreadFactory {
+    private int cnt;
+
+    @Override
+    public @NotNull Thread newThread(final @NotNull Runnable r) {
+      final Thread ret = new Thread(r, "SentryExecutorServiceThreadFactory-" + cnt++);
+      ret.setDaemon(true);
+      return ret;
+    }
+  }
 }