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Add Stage 3 Lesson 3
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‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/pom.xml

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<modules>
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<module>stage-3-lesson-1</module>
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<module>stage-3-lesson-2</module>
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<module>stage-3-lesson-3</module>
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</modules>
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<packaging>pom</packaging>
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‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>stage-3</artifactId>
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<groupId>com.segmentfault</groupId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>stage-3-lesson-3</artifactId>
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<name>「一入 Java 深似海 」系列 :: 第三期 :: 第三节</name>
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</project>

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/AcquireAndReleaseDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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public class AcquireAndReleaseDemo {
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public static void main(String[] args) {
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//　Lock　机制
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// 获得 Acquire
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// Thread 进入 synchronized -> 获得锁
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// 释放 Release
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// 1. 当 Thread（hold lock），调用 Object#wait() 时候
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// 2. Thread park -> LockSupport.park(Object)
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// 3. Condition#await()
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// 4. 运行期异常，Thread 消亡
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// 5. Java 9 自旋 Thread.onSpinWait();
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// 6. Thread.yield();
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// 所谓的公平（Fair）和非公平（Nonfair、unfair）
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// 公平（Fair）线程 FIFO
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// 非公平（Nonfair）线程随线程调度
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// 最佳实践：在创建线程时，除非必要，不要调整线程优先级（Priority）
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/AtomicDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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import sun.misc.Unsafe;
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import java.lang.invoke.MethodHandles;
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import java.lang.invoke.VarHandle;
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import java.lang.reflect.Field;
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import java.security.AccessController;
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import java.security.PrivilegedActionException;
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import java.security.PrivilegedExceptionAction;
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import java.util.concurrent.atomic.AtomicBoolean;
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import java.util.concurrent.atomic.AtomicLong;
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public class AtomicDemo {
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public static void main(String[] args) throws Exception {
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// CAS 是一种相对（MB）较重的比较，轻量级的锁（标量）
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getUnsafe();
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// volatile 修饰复杂对象类型时，不具备被传递到字段安全
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}
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private static void demoAtomicLong() {
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// long 表示 64位（8字节），高和低两端
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// long 并非线程安全，就是 volatile（高和低操作时，至少两次操作）
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AtomicLong l = new AtomicLong();
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// set 和 get 通过 JVM 特殊操作，不在直接写入和获取
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}
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private static void demoAtomicInteger() {
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// int 表示 int(32), char(16), short(16), byte(8), boolean(1)
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// AtomicInteger 内部使用 int 作为变量标识，1 表示 true, 0 表示 false
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// AtomicInteger set 和 get 操作均为 volatile 语义（MB）
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// AtomicInteger CAS Unsafe(Java 8) 和 VarHandle（Java 9+）
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}
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private static void demoAtomicBoolean() {
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AtomicBoolean b = new AtomicBoolean();
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// AtomicBoolean 内部使用 int 作为变量标识，1 表示 true, 0 表示 false
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// AtomicBoolean set 和 get 操作均为 volatile 语义（MB）
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// AtomicBoolean CAS Unsafe(Java 8) 和 VarHandle（Java 9+）
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}
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private static void getVarHandle() {
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MethodHandles.Lookup l = MethodHandles.lookup();
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}
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private static void getUnsafe() throws PrivilegedActionException {
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// 无法通过正常方法调用
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// Unsafe unsafe = Unsafe.getUnsafe();
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// https://github.com/mercyblitz/confucius-commons/blob/master/confucius-commons-lang/src/main/java/org/confucius/commons/lang/misc/UnsafeUtils.java
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final PrivilegedExceptionAction<Unsafe> action = new PrivilegedExceptionAction<Unsafe>() {
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public Unsafe run() throws Exception {
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Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
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theUnsafe.setAccessible(true);
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return (Unsafe) theUnsafe.get(null);
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}
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};
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Unsafe unsafe = AccessController.doPrivileged(action);
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if (unsafe == null) {
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throw new NullPointerException();
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}
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/CountDownLatchDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.ExecutorService;
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import java.util.concurrent.Executors;
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public class CountDownLatchDemo {
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public static void main(String[] args) throws InterruptedException {
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// 4 -> 3 -> 2 -> 1
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CountDownLatch latch = new CountDownLatch(4); // 4 个计数
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ExecutorService executorService = Executors.newFixedThreadPool(3); // 线程数 3
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for (int i = 0; i < 3; i++) { // 启动3个线程
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executorService.submit(() -> {
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try {
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echoThread();
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latch.countDown(); // -1
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} catch (Exception e) {
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e.printStackTrace();
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}
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});
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}
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Thread.sleep(5 * 100);
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// 当 count 数量等于 0，才会释放
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// 4-3 == 1 !=0
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System.out.println("CountDownLatch 剩余数量：" + latch.getCount());
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latch.await(); // await 类似 wait() -> join
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// 关闭线程池
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executorService.shutdown();
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}
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private static void echoThread() {
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System.out.printf("当前线程[%s]正在执行...\n", Thread.currentThread().getName());
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/CyclicBarrierDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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import java.util.concurrent.BrokenBarrierException;
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import java.util.concurrent.CyclicBarrier;
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import java.util.concurrent.ExecutorService;
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import java.util.concurrent.Executors;
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public class CyclicBarrierDemo {
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public static void main(String[] args) throws BrokenBarrierException, InterruptedException {
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CyclicBarrier cb = new CyclicBarrier(4);
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ExecutorService executorService = Executors.newFixedThreadPool(3);
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for (int i = 0; i < 3; i++) {
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executorService.submit(() -> {
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try {
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echoThread();
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cb.await(); // await() 让计数 -1
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} catch (Exception e) {
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e.printStackTrace();
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}
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});
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}
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Thread.sleep(5 * 100);
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// 当 count 数量等于 0，才会释放
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// 4 - 3 == 1 !=0
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// 再次 await() -1 => 4 - 3 - 1 = 0
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System.out.println(cb.getNumberWaiting());
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cb.await();
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System.out.println(cb.getNumberWaiting());
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// // reset() 操作是恢复计数 0 -> 4
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cb.reset();
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System.out.println(cb.getNumberWaiting());
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//
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// 关闭线程池
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executorService.shutdown();
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}
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private static void echoThread() {
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System.out.printf("当前线程[%s]正在执行...\n", Thread.currentThread().getName());
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/ReentrantLockDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.locks.Condition;
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import java.util.concurrent.locks.Lock;
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import java.util.concurrent.locks.ReentrantLock;
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public class ReentrantLockDemo {
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public static void main(String[] args) {
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lockOpsMethods();
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}
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private static void lockOpsMethods() {
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ReentrantLock lock = new ReentrantLock();
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int count = lock.getHoldCount();
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System.out.printf("在 lock() 方法调用之前的线程[%s]重进入数：%d\n", Thread.currentThread().getName(), count);
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lock(lock, 100);
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}
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private static void lock(ReentrantLock lock, int times) {
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if (times < 1) {
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return;
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}
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lock.lock();
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try {
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// times-- load, minus 1
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lock(lock, --times);
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System.out.printf("第%s次在 lock() 方法调用之后的线程[%s]重进入数：%d\n",
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times+1,
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Thread.currentThread().getName(),
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lock.getHoldCount());
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} finally {
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lock.unlock();
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}
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}
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private static void conditionObject() {
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Lock lock = new ReentrantLock();
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// 条件变量包括条件，同时它又是线程通讯媒介
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Condition condition = lock.newCondition();
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try {
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condition.await();
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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private static void tryLockInTimeout() {
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Lock lock = new ReentrantLock();
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try {
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if (lock.tryLock(3, TimeUnit.SECONDS)) { // 当前仅当在规定的时间内获得锁
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// Lock API 语义补充了 synchronized 原语的不足
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// TODO Add some logic
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}
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} catch (InterruptedException e) {
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// 重置中止状态（防止被中途清除 interrupt 状态）
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Thread.currentThread().interrupt();
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// logger error message
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}
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}
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private static void synchronizedStatement() {
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// 假设出现死锁或者饥饿
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synchronized (ReentrantLockDemo.class) {
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if (3 > 2) { // 条件
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try {
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ReentrantLockDemo.class.wait(); // Object 线程通讯方法
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} catch (InterruptedException e) {
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// logger error message
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}
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}
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}
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/ReentrantReadWriteLockDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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import java.util.concurrent.locks.Lock;
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import java.util.concurrent.locks.ReadWriteLock;
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import java.util.concurrent.locks.ReentrantReadWriteLock;
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public class ReentrantReadWriteLockDemo {
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public static void main(String[] args) {
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ReadWriteLock lock = new ReentrantReadWriteLock();
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Lock readLock = lock.readLock();
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Lock writeLock = lock.writeLock();
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/SemaphoreDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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import java.util.concurrent.*;
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public class SemaphoreDemo {
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public static void main(String[] args) throws BrokenBarrierException, InterruptedException {
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Semaphore cb = new Semaphore(4);
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ExecutorService executorService = Executors.newFixedThreadPool(3);
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for (int i = 0; i < 3; i++) {
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executorService.submit(() -> {
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try {
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echoThread();
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cb.acquire(); // await() 让计数 -1
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} catch (Exception e) {
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e.printStackTrace();
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}
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});
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}
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Thread.sleep(5 * 100);
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// 当 count 数量等于 0，才会释放
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// 4 - 3 == 1 !=0
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// 再次 await() -1 => 4 - 3 - 1 = 0
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//
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// 关闭线程池
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executorService.shutdown();
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}
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private static void echoThread() {
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System.out.printf("当前线程[%s]正在执行...\n", Thread.currentThread().getName());
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-3/stage-3-lesson-3/src/main/java/com/segmentfault/deep/in/java/concurrency/StampedLockDemo.java

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package com.segmentfault.deep.in.java.concurrency;
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import java.util.concurrent.locks.Lock;
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import java.util.concurrent.locks.StampedLock;
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public class StampedLockDemo {
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public static void main(String[] args) {
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// Java 1.8 之后提供
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StampedLock lock = new StampedLock();
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long stamp = lock.tryOptimisticRead();
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Lock readLock = lock.asReadLock();
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try {
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readLock.lock();
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lock.validate(stamp);
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} finally {
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readLock.unlock();
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}
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}
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}

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