#2582 - Fix for regression, BackgroundExecutor is bounded (since 12.6.2)

The change for #2121 brought in a regression where the scheduledExecutorService was used for processing ALL submitted tasks (not just scheduled ones) and is a bounded executor service.  Previously non-scheduled tasks went to a "newCachedThreadPool" based executor service and with this change we are moving back to that (via restoring and using the DaemonExecutorService for those tasks).

ebean-core/src/test/java/io/ebeaninternal/server/executor/DaemonExecutorServiceTest.java

@@ -0,0 +1,56 @@
+package io.ebeaninternal.server.executor;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Future;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class DaemonExecutorServiceTest {
+
+  private final int count = 10;
+  private final int waitMillis = 100;
+
+  @Test
+  void submit() throws Exception {
+    DaemonExecutorService des = new DaemonExecutorService(5, "junk");
+    long start = System.currentTimeMillis();
+    List<Future<?>> futures = new ArrayList<>();
+    for (int i = 0; i < count; i++) {
+      futures.add(des.submit(this::doStuff));
+    }
+    for (Future<?> f: futures) {
+      f.get();
+    }
+    long exeMillis = System.currentTimeMillis() - start;
+    assertThat(exeMillis).isLessThan(count * waitMillis);
+    des.shutdown();
+  }
+
+  @Test
+  void submit_via_DefaultBackgroundExecutor() throws Exception {
+    DefaultBackgroundExecutor des = new DefaultBackgroundExecutor(1, 5, "junk");
+    long start = System.currentTimeMillis();
+    List<Future<?>> futures = new ArrayList<>();
+    for (int i = 0; i < count; i++) {
+      futures.add(des.submit(this::doStuff));
+    }
+    for (Future<?> f: futures) {
+      f.get();
+    }
+    long exeMillis = System.currentTimeMillis() - start;
+    assertThat(exeMillis).isLessThan(count * waitMillis);
+    des.shutdown();
+  }
+
+  private void doStuff() {
+    try {
+      Thread.sleep(waitMillis);
+    } catch (InterruptedException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+}