[MNG-7899] Various memory usage improvements

- Non-threadsafe FileSizeFormat instance can be make class instance
since its formatProgress() method is only called in a synchronized
block.

- add a test in a multi-threaded context

maven-embedder/src/main/java/org/apache/maven/cli/transfer/ConsoleMavenTransferListener.java

@@ -36,6 +36,7 @@
 public class ConsoleMavenTransferListener extends AbstractMavenTransferListener {
 
     private Map<TransferResource, Long> transfers = Collections.synchronizedMap(new LinkedHashMap<>());
+    private FileSizeFormat format = new FileSizeFormat(Locale.ENGLISH); // use in a synchronized fashion
 
     private boolean printResourceNames;
     private int lastLength;
@@ -68,8 +69,6 @@ public synchronized void transferProgressed(TransferEvent event) throws Transfer
         buffer.append("Progress (").append(transfers.size()).append("): ");
 
         synchronized (transfers) {
-            FileSizeFormat format = new FileSizeFormat(Locale.ENGLISH);
-
             Iterator<Map.Entry<TransferResource, Long>> entries =
                     transfers.entrySet().iterator();
             while (entries.hasNext()) {

maven-embedder/src/test/java/org/apache/maven/cli/transfer/ConsoleMavenTransferListenerTest.java

@@ -0,0 +1,102 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.cli.transfer;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.FileNotFoundException;
+import java.io.PrintStream;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import org.eclipse.aether.DefaultRepositorySystemSession;
+import org.eclipse.aether.transfer.TransferCancelledException;
+import org.eclipse.aether.transfer.TransferEvent;
+import org.eclipse.aether.transfer.TransferResource;
+import org.junit.jupiter.api.Test;
+
+class ConsoleMavenTransferListenerTest {
+
+    private CountDownLatch latch;
+
+    @Test
+    void testTransferProgressedWithPrintResourceNames() throws FileNotFoundException, InterruptedException {
+        int size = 1000;
+        ExecutorService service = Executors.newFixedThreadPool(1000);
+        latch = new CountDownLatch(size);
+        Map<String, String> output = new ConcurrentHashMap<String, String>();
+
+        ConsoleMavenTransferListener listener = new ConsoleMavenTransferListener(
+                new PrintStream(System.out) {
+
+                    @Override
+                    public void print(Object o) {
+                        String string = o.toString()
+                                .substring(0, o.toString().length() - 1)
+                                .trim();
+                        output.put(string, string);
+                        System.out.print(o);
+                    }
+                },
+                true);
+        TransferResource resource = new TransferResource(null, null, "http://maven.org/test/test-resource", null, null);
+        resource.setContentLength(size - 1);
+
+        DefaultRepositorySystemSession session = new DefaultRepositorySystemSession();
+
+        // warm up
+        test(listener, session, resource, 0);
+
+        for (int i = 1; i < size; i++) {
+            final int bytes = i;
+
+            service.execute(() -> {
+                test(listener, session, resource, bytes);
+            });
+        }
+        try {
+            latch.await();
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+
+        boolean test = true;
+        for (int i = 0; i < 999; i++) {
+            boolean ok = output.containsKey("Progress (1): test-resource (" + i + "/999 B)");
+            if (!ok) {
+                System.out.println("false : " + i);
+            }
+            test = test & ok;
+        }
+        assertTrue(test);
+    }
+
+    private void test(ConsoleMavenTransferListener listener, DefaultRepositorySystemSession session, TransferResource resource, final int bytes) {
+        TransferEvent event = new TransferEvent.Builder(session, resource)
+                .setTransferredBytes(bytes).build();
+        latch.countDown();
+        try {
+            listener.transferProgressed(event);
+        } catch (TransferCancelledException e) {
+        }
+    }
+}