feat: concurrency example

Author: fghpdf

src/com/fghpdf/Concurrency/VolatileAtomic.java

@@ -0,0 +1,32 @@
+package com.fghpdf.Concurrency;
+
+/**
+ * @author fghpdf
+ * @date 2019/11/16
+ **/
+public class VolatileAtomic {
+	private static volatile int num = 0;
+
+	private static void atom() {
+		num++;
+	}
+
+	public static void main(String[] args) throws InterruptedException {
+		Thread[] threads = new Thread[10];
+
+		for (int i = 0; i < threads.length; i++) {
+			threads[i] = new Thread(() -> {
+				for (int j = 0; j < 1000; j++) {
+					atom();
+				}
+			});
+			threads[i].start();
+		}
+
+		for (Thread t : threads) {
+			t.join();
+		}
+
+		System.out.println(num);
+	}
+}

src/com/fghpdf/Concurrency/VolatileVisibility.java

@@ -0,0 +1,28 @@
+package com.fghpdf.Concurrency;
+
+/**
+ * @author fghpdf
+ * @date 2019/11/16
+ **/
+public class VolatileVisibility {
+	// volatile
+	private static volatile boolean initFlag = false;
+
+	public static void main(String[] args) throws InterruptedException {
+		new Thread(() -> {
+			System.out.println("waiting data ...");
+			while (!initFlag) {
+
+			}
+			System.out.println("done");
+		}).start();
+
+		Thread.sleep(2000);
+
+		new Thread(() -> {
+			System.out.println("change data");
+			initFlag = true;
+			System.out.println("changed");
+		}).start();
+	}
+}