#1869 - out of order nextId() sequence generation

src/main/java/io/ebean/config/dbplatform/SequenceIdGenerator.java

@@ -12,9 +12,10 @@ import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.NavigableSet;
+import java.util.TreeSet;
 
 /**
  * Database sequence based IdGenerator.
@@ -42,7 +43,7 @@ public abstract class SequenceIdGenerator implements PlatformIdGenerator {
 
   protected final BackgroundExecutor backgroundExecutor;
 
-  protected final ArrayList<Long> idList = new ArrayList<>(50);
+  protected final NavigableSet<Long> idList = new TreeSet<>();
 
   protected final int allocationSize;
 
@@ -97,15 +98,13 @@ public abstract class SequenceIdGenerator implements PlatformIdGenerator {
   @Override
   public Object nextId(Transaction t) {
     synchronized (monitor) {
-
       int size = idList.size();
       if (size > 0) {
         maybeLoadMoreInBackground(size);
       } else {
         loadMore(allocationSize);
       }
-
-      return idList.remove(0);
+      return idList.pollFirst();
     }
   }
 

src/test/java/io/ebean/config/dbplatform/SequenceBatchIdGeneratorTest.java

@@ -0,0 +1,62 @@
+package io.ebean.config.dbplatform;
+
+import org.junit.Test;
+
+import java.sql.ResultSet;
+import java.util.List;
+
+import static java.util.Arrays.asList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class SequenceBatchIdGeneratorTest {
+
+  @Test
+  public void test() {
+
+    TD generator = new TD();
+
+    // simulate out of order adding of sequence ids
+    generator.add(asList(1L, 2L));
+    generator.add(asList(5L, 6L));
+    generator.add(asList(3L, 4L));
+
+    assertThat(generator.nextId(null)).isEqualTo(1L);
+    assertThat(generator.nextId(null)).isEqualTo(2L);
+    assertThat(generator.nextId(null)).isEqualTo(3L);
+    assertThat(generator.nextId(null)).isEqualTo(4L);
+    assertThat(generator.nextId(null)).isEqualTo(5L);
+    assertThat(generator.nextId(null)).isEqualTo(6L);
+  }
+
+  private class TD extends SequenceIdGenerator {
+
+    protected TD() {
+      super(null, null, null, 10);
+    }
+
+    void add(List<Long> ids) {
+      idList.addAll(ids);
+    }
+
+    @Override
+    public String getSql(int batchSize) {
+      return "not used";
+    }
+
+    @Override
+    protected List<Long> readIds(ResultSet resultSet, int loadSize) {
+      // do nothing
+      return null;
+    }
+
+    @Override
+    protected List<Long> getMoreIds(int requestSize) {
+      return null;
+    }
+
+    @Override
+    protected void loadInBackground(int requestSize) {
+      // do nothing
+    }
+  }
+}