BAEL-7699 Avoid busy-waiting examples (#18677)

* BAEL-7699 Avoid busy-waiting examples

* BAEL-7699 Improve test readability

* BAEL-7699 Naming improvements

Author: apelan

core-java-modules/core-java-concurrency-basic-4/src/test/java/com/baeldung/concurrent/busywaiting/BusyWaitingManualTest.java

@@ -0,0 +1,78 @@
+package com.baeldung.concurrent.busywaiting;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class BusyWaitingManualTest {
+
+    private static final Logger logger = LoggerFactory.getLogger(BusyWaitingManualTest.class);
+
+    @Test
+    void givenWorkerThread_whenBusyWaiting_thenAssertExecutedMultipleTimes() {
+        AtomicBoolean taskDone = new AtomicBoolean(false);
+        long counter = 0;
+
+        Thread worker = new Thread(() -> {
+            simulateThreadWork();
+            taskDone.set(true);
+        });
+
+        worker.start();
+
+        while (!taskDone.get()) {
+            counter++;
+        }
+
+        logger.info("Counter: {}", counter);
+        assertNotEquals(1, counter);
+    }
+
+    @Test
+    void givenWorkerThread_whenUsingWaitNotify_thenWaitEfficientlyOnce() {
+        AtomicBoolean taskDone = new AtomicBoolean(false);
+        final Object monitor = new Object();
+        long counter = 0;
+
+        Thread worker = new Thread(() -> {
+            simulateThreadWork();
+            synchronized (monitor) {
+                taskDone.set(true);
+                monitor.notify();
+            }
+        });
+
+        worker.start();
+
+        synchronized (monitor) {
+            while (!taskDone.get()) {
+                counter++;
+                try {
+                    monitor.wait();
+                } catch (InterruptedException e) {
+                    Thread.currentThread()
+                        .interrupt();
+                    fail("Test case failed due to thread interruption!");
+                }
+            }
+        }
+
+        assertEquals(1, counter);
+    }
+
+    private void simulateThreadWork() {
+        try {
+            Thread.sleep(500);
+        } catch (InterruptedException e) {
+            Thread.currentThread()
+                .interrupt();
+        }
+    }
+
+}