add flag to make CSV upload wait until entries are flushed

To make it easier/possible to write stable unit test the CSV upload
can optionally wait until all entries have been flushed to disk.
This is necessary for tests that ingest data and then read the data.

pdb-api/src/main/java/org/lucares/pdb/api/Entries.java

@@ -5,7 +5,24 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 
+/**
+ * Wrapper for chunk of {@link Entry}s.
+ * <p>
+ * This class is supposed to be provided to the queue returned by
+ * PerformanceDb.getQueue(). Processing {@link Entry}s in chunks is more
+ * efficient than processing each one individually.
+ * <p>
+ * Optionally, you can request that the entries will be flushed to disk by
+ * calling {@link #forceFlush()} before adding it to the queue.
+ * <p>
+ * Optionally, this class can act like a future. This is useful if you have to
+ * wait until the entries have been processed. Use {@link #forceFlush()} and
+ * {@link #waitUntilFlushed(long, TimeUnit)}.
+ */
 public class Entries implements Iterable<Entry> {
     /**
      * A special {@link Entries} instance that can be used as poison object for
@@ -15,6 +32,10 @@ public class Entries implements Iterable<Entry> {
 
     private final List<Entry> entries;
 
+    private boolean forceFlush = false;
+
+    private CountDownLatch flushLatch = null;
+
     public Entries(final int initialSize) {
         entries = new ArrayList<>(initialSize);
     }
@@ -39,4 +60,25 @@ public class Entries implements Iterable<Entry> {
     public int size() {
         return entries.size();
     }
+
+    public boolean isForceFlush() {
+        return forceFlush;
+    }
+
+    public void forceFlush() {
+        forceFlush = true;
+        flushLatch = new CountDownLatch(1);
+    }
+
+    public void waitUntilFlushed(final long timeout, final TimeUnit unit)
+            throws InterruptedException, TimeoutException {
+        final boolean finished = flushLatch.await(timeout, unit);
+        if (!finished) {
+            throw new TimeoutException();
+        }
+    }
+
+    public void notifyFlushed() {
+        flushLatch.countDown();
+    }
 }