[MNG-7899] Various memory usage improvements 4 (#1269)

- Use the main StringBuilder to append string instead of using a separate one
- Use the StringBuilder.append() with index to avoid String.substring(), less temporary strings
- Reuse the FileSizeFormat object in the while loop avoiding multiple temporary instances creation
- 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
- Non-threadsafe StringBuilder instance 'buffer' can be make class instance since it is always called in synchronized methods
- remove synchronized block in transferProgressed() method, the method is synchronized and the block is not needed
- Remove the Collections.synchronizedMap since all methods that use the transfers map are synchronized

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

@@ -19,7 +19,6 @@
 package org.apache.maven.cli.transfer;
 
 import java.io.PrintStream;
-import java.util.Collections;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.Locale;
@@ -35,7 +34,9 @@ import org.eclipse.aether.transfer.TransferResource;
  */
 public class ConsoleMavenTransferListener extends AbstractMavenTransferListener {
 
-    private Map<TransferResource, Long> transfers = Collections.synchronizedMap(new LinkedHashMap<>());
+    private Map<TransferResource, Long> transfers = new LinkedHashMap<>();
+    private FileSizeFormat format = new FileSizeFormat(Locale.ENGLISH); // use in a synchronized fashion
+    private StringBuilder buffer = new StringBuilder(128); // use in a synchronized fashion
 
     private boolean printResourceNames;
     private int lastLength;
@@ -64,20 +65,36 @@ public class ConsoleMavenTransferListener extends AbstractMavenTransferListener
         TransferResource resource = event.getResource();
         transfers.put(resource, event.getTransferredBytes());
 
-        StringBuilder buffer = new StringBuilder(128);
         buffer.append("Progress (").append(transfers.size()).append("): ");
 
-        synchronized (transfers) {
+        Iterator<Map.Entry<TransferResource, Long>> entries =
-            Iterator<Map.Entry<TransferResource, Long>> entries =
+                transfers.entrySet().iterator();
-                    transfers.entrySet().iterator();
+        while (entries.hasNext()) {
-            while (entries.hasNext()) {
+            Map.Entry<TransferResource, Long> entry = entries.next();
-                Map.Entry<TransferResource, Long> entry = entries.next();
+            long total = entry.getKey().getContentLength();
-                long total = entry.getKey().getContentLength();
+            Long complete = entry.getValue();
-                Long complete = entry.getValue();
+
-                buffer.append(getStatus(entry.getKey().getResourceName(), complete, total));
+            String resourceName = entry.getKey().getResourceName();
-                if (entries.hasNext()) {
+
-                    buffer.append(" | ");
+            if (printResourceNames) {
+                int idx = resourceName.lastIndexOf('/');
+
+                if (idx < 0) {
+                    buffer.append(resourceName);
+                } else {
+                    buffer.append(resourceName, idx + 1, resourceName.length());
                 }
+                buffer.append(" (");
+            }
+
+            buffer.append(format.formatProgress(complete, total));
+
+            if (printResourceNames) {
+                buffer.append(")");
+            }
+
+            if (entries.hasNext()) {
+                buffer.append(" | ");
             }
         }
 
@@ -87,25 +104,7 @@ public class ConsoleMavenTransferListener extends AbstractMavenTransferListener
         buffer.append('\r');
         out.print(buffer);
         out.flush();
-    }
+        buffer.setLength(0);
-
-    private String getStatus(String resourceName, long complete, long total) {
-        FileSizeFormat format = new FileSizeFormat(Locale.ENGLISH);
-        StringBuilder status = new StringBuilder();
-
-        if (printResourceNames) {
-            int idx = resourceName.lastIndexOf('/');
-            status.append(idx < 0 ? resourceName : resourceName.substring(idx + 1));
-            status.append(" (");
-        }
-
-        status.append(format.formatProgress(complete, total));
-
-        if (printResourceNames) {
-            status.append(")");
-        }
-
-        return status.toString();
     }
 
     private void pad(StringBuilder buffer, int spaces) {
@@ -135,12 +134,12 @@ public class ConsoleMavenTransferListener extends AbstractMavenTransferListener
 
     private void overridePreviousTransfer(TransferEvent event) {
         if (lastLength > 0) {
-            StringBuilder buffer = new StringBuilder(128);
             pad(buffer, lastLength);
             buffer.append('\r');
             out.print(buffer);
             out.flush();
             lastLength = 0;
+            buffer.setLength(0);
         }
     }
 }

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

@@ -0,0 +1,128 @@
+/*
+ * 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 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;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class ConsoleMavenTransferListenerTest {
+
+    private CountDownLatch startLatch;
+    private CountDownLatch endLatch;
+
+    @Test
+    void testTransferProgressedWithPrintResourceNames() throws FileNotFoundException, InterruptedException {
+        int size = 1000;
+        ExecutorService service = Executors.newFixedThreadPool(size * 2);
+        startLatch = new CountDownLatch(size);
+        endLatch = 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();
+                        int i = string.length() - 1;
+                        while (i >= 0) {
+                            char c = string.charAt(i);
+                            if (c == '\n' || c == '\r' || c == ' ') i--;
+                            else break;
+                        }
+
+                        string = string.substring(0, i + 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);
+            });
+        }
+
+        // start all threads at once
+        try {
+            startLatch.await();
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+
+        // wait for all thread to end
+        try {
+            endLatch.await();
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+
+        StringBuilder message = new StringBuilder("Messages [");
+        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);
+                message.append(i + ",");
+            }
+            test = test & ok;
+        }
+        assertTrue(test, message.toString() + "] are missiong in " + output);
+    }
+
+    private void test(
+            ConsoleMavenTransferListener listener,
+            DefaultRepositorySystemSession session,
+            TransferResource resource,
+            final int bytes) {
+        TransferEvent event = new TransferEvent.Builder(session, resource)
+                .setTransferredBytes(bytes)
+                .build();
+        startLatch.countDown();
+        try {
+            listener.transferProgressed(event);
+        } catch (TransferCancelledException e) {
+        }
+        endLatch.countDown();
+    }
+}