Add first example on how to use the new buffer API

src/test/java/io/netty/buffer/api/examples/FileCopyExample.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright 2020 The Netty Project
+ *
+ * The Netty Project 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:
+ *
+ *   https://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 io.netty.buffer.api.examples;
+
+import io.netty.buffer.api.Allocator;
+import io.netty.buffer.api.Buf;
+import io.netty.buffer.api.Send;
+
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.Path;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import static java.nio.file.StandardOpenOption.CREATE;
+import static java.nio.file.StandardOpenOption.READ;
+import static java.nio.file.StandardOpenOption.TRUNCATE_EXISTING;
+import static java.nio.file.StandardOpenOption.WRITE;
+
+public final class FileCopyExample {
+    public static void main(String[] args) throws Exception {
+        ExecutorService executor = Executors.newFixedThreadPool(2);
+        ArrayBlockingQueue<Object> queue = new ArrayBlockingQueue<>(8);
+        Object done = new Object();
+        try (Allocator allocator = Allocator.pooledDirect();
+             var input = FileChannel.open(Path.of("/dev/urandom"), READ);
+             var output = FileChannel.open(Path.of("random.bin"), CREATE, TRUNCATE_EXISTING, WRITE)) {
+
+            var reader = executor.submit(() -> {
+                var buf = ByteBuffer.allocateDirect(1024);
+                for (int i = 0; i < 1024; i++) {
+                    buf.clear();
+                    while (buf.hasRemaining()) {
+                        int r = input.read(buf);
+                        System.out.println("r = " + r);
+                        System.out.println("buf = " + buf);
+                    }
+                    buf.flip();
+                    try (Buf in = allocator.allocate(1024)) {
+                        System.out.println("in = " + in);
+                        while (buf.hasRemaining()) {
+                            in.writeByte(buf.get());
+                        }
+                        System.out.println("Sending " + in.readableBytes() + " bytes.");
+                        queue.put(in.send());
+                    }
+                }
+                queue.put(done);
+                return null;
+            });
+
+            var writer = executor.submit(() -> {
+                var buf = ByteBuffer.allocateDirect(1024);
+                Object msg;
+                while ((msg = queue.take()) != done) {
+                    buf.clear();
+                    @SuppressWarnings("unchecked")
+                    Send<Buf> send = (Send<Buf>) msg;
+                    try (Buf out = send.receive()) {
+                        System.out.println("Received " + out.readableBytes() + " bytes.");
+                        out.copyInto(0, buf, 0, out.readableBytes());
+                        buf.position(0).limit(out.readableBytes());
+                    }
+                    while (buf.hasRemaining()) {
+                        output.write(buf);
+                    }
+                }
+                output.force(true);
+                return null;
+            });
+
+            reader.get();
+            writer.get();
+        } finally {
+            executor.shutdown();
+        }
+    }
+}