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java并发问题的实现方案
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170
Java/04Java并发编程/12 生产者消费者.md
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170
Java/04Java并发编程/12 生产者消费者.md
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Java生产者-消费者问题的多种实现方案
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以下是5种典型实现方式，涵盖从基础同步到高阶工具的使用：
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## 1. wait()/notify() 基础同步（JDK1.0+）
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核心逻辑：通过synchronized和对象锁协调线程。
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```
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// 共享缓冲区类
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class Buffer {
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private final LinkedList<Object> list = new LinkedList<>();
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private final int MAX_SIZE = 10;
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public synchronized void produce() throws InterruptedException {
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while (list.size() >= MAX_SIZE) {
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wait(); // 缓冲区满时等待<sup>2</sup><sup>7</sup>
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}
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list.add(new Object());
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System.out.println("生产, 当前库存: " + list.size());
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notifyAll(); // 唤醒消费者<sup>9</sup>
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}
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public synchronized void consume() throws InterruptedException {
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while (list.isEmpty()) {
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wait(); // 缓冲区空时等待<sup>7</sup><sup>9</sup>
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}
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list.remove();
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System.out.println("消费, 当前库存: " + list.size());
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notifyAll(); // 唤醒生产者<sup>2</sup>
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}
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}
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```
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特点：需手动管理锁，易出现死锁，适合理解底层机制17。
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## 2. Lock与Condition（JDK5+）
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核心逻辑：通过显式锁和条件变量精细化控制。
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```
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import java.util.concurrent.locks.*;
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class Buffer {
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private final Lock lock = new ReentrantLock();
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private final Condition notFull = lock.newCondition();
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private final Condition notEmpty = lock.newCondition();
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private final int MAX_SIZE = 10;
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private LinkedList<Object> list = new LinkedList<>();
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public void produce() throws InterruptedException {
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lock.lock();
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try {
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while (list.size() >= MAX_SIZE) {
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notFull.await(); // 等待非满条件<sup>7</sup>
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}
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list.add(new Object());
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System.out.println("生产, 当前库存: " + list.size());
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notEmpty.signalAll(); // 通知非空条件<sup>7</sup>
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} finally {
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lock.unlock();
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}
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}
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public void consume() throws InterruptedException {
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lock.lock();
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try {
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while (list.isEmpty()) {
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notEmpty.await(); // 等待非空条件<sup>7</sup>
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}
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list.remove();
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System.out.println("消费, 当前库存: " + list.size());
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notFull.signalAll(); // 通知非满条件<sup>7</sup>
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} finally {
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lock.unlock();
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}
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}
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}
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```
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特点：支持多条件变量，避免虚假唤醒，灵活性高78。
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## 3. BlockingQueue 阻塞队列（JDK5+）
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核心逻辑：利用线程安全队列自动处理阻塞。
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```
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import java.util.concurrent.BlockingQueue;
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import java.util.concurrent.LinkedBlockingQueue;
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public class Main {
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public static void main(String[] args) {
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BlockingQueue<Object> queue = new LinkedBlockingQueue<>(10); // 容量限制<sup>3</sup><sup>10</sup>
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// 生产者
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new Thread(() -> {
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while (true) {
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try {
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queue.put(new Object()); // 队列满时自动阻塞<sup>4</sup><sup>6</sup>
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System.out.println("生产, 当前库存: " + queue.size());
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} catch (InterruptedException e) {
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Thread.currentThread().interrupt();
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}
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}
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}).start();
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// 消费者 new Thread(() -> {
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while (true) {
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try {
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queue.take(); // 队列空时自动阻塞<sup>3</sup><sup>10</sup>
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System.out.println("消费, 当前库存: " + queue.size());
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} catch (InterruptedException e) {
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Thread.currentThread().interrupt();
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}
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}
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}).start();
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}
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}
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```
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特点：代码简洁，无需手动同步，推荐生产环境使用3610。
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## 4. 信号量 Semaphore（JDK5+）
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核心逻辑：通过许可控制资源访问。
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```
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import java.util.concurrent.Semaphore;
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class Buffer {
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private final Semaphore emptySlots = new Semaphore(10); // 初始空位数量<sup>7</sup>
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private final Semaphore filledSlots = new Semaphore(0); // 初始已用数量<sup>7</sup>
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private final LinkedList<Object> list = new LinkedList<>();
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public void produce() throws InterruptedException {
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emptySlots.acquire(); // 获取空位许可<sup>7</sup>
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synchronized (this) {
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list.add(new Object());
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System.out.println("生产, 当前库存: " + list.size());
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}
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filledSlots.release(); // 释放已用许可<sup>7</sup>
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}
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public void consume() throws InterruptedException {
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filledSlots.acquire(); // 获取已用许可<sup>7</sup>
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synchronized (this) {
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list.remove();
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System.out.println("消费, 当前库存: " + list.size());
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}
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emptySlots.release(); // 释放空位许可<sup>7</sup>
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}
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}
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```
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特点：适合控制并发资源数，但需结合同步块保证原子性78。
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## 5. 管道通信（不推荐）
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核心逻辑：通过PipedInputStream/PipedOutputStream传输数据。
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```
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import java.io.*;
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public class PipeExample {
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public static void main(String[] args) throws IOException {
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PipedInputStream pis = new PipedInputStream();
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PipedOutputStream pos = new PipedOutputStream();
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pos.connect(pis); // 连接管道<sup>7</sup>
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// 生产者写数据
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new Thread(() -> {
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try {
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pos.write("data".getBytes());
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pos.close();
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} catch (IOException e) {
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e.printStackTrace();
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}
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}).start();
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// 消费者读数据
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new Thread(() -> {
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try {
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int data;
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while ((data = pis.read()) != -1) {
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System.out.print((char) data);
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}
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pis.close();
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} catch (IOException e) {
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e.printStackTrace();
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}
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}).start();
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}
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}
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```
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特点：数据流式传输，但难以控制缓冲区，实际应用较少7。
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## 推荐优先级：
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BlockingQueue > Lock/Condition > 信号量 > wait()/notify() > 管道
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92
Java/04Java并发编程/13 读写锁问题.md
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Java/04Java并发编程/13 读写锁问题.md
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# 读写锁问题
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读的时候共享、写的时候独占。
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## 方案一：ReentrantReadWriteLock（推荐方案）
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核心特性：
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读锁共享：允许多线程并发读取
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写锁独占：写操作时完全互斥135
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锁降级：写线程可降级为读锁，保证数据一致性
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```
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import java.util.concurrent.locks.*;
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public class ReadWriteResource {
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private int value;
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private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
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private final Lock readLock = rwLock.readLock();
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private final Lock writeLock = rwLock.writeLock();
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// 读操作（共享）
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public int readValue() {
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readLock.lock();
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try {
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return value;
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} finally {
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readLock.unlock();
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}
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}
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// 写操作（独占）
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public void writeValue(int newValue) {
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writeLock.lock();
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try {
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value = newValue;
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} finally {
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writeLock.unlock();
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}
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}
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}
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```
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优势：
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明确的读写分离，符合业务语义35
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支持公平/非公平锁策略19
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读操作完全无阻塞，适合读多写少场景15
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## 方案二：StampedLock（高性能方案）
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核心特性：
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乐观读：无锁读取，通过版本号校验数据一致性28
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悲观读：类似ReentrantReadWriteLock的读锁8
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写锁独占：与所有读操作互斥
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```
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import java.util.concurrent.locks.*;
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public class StampedResource {
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private int value;
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private final StampedLock stampedLock = new StampedLock();
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// 乐观读（无锁）
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public int optimisticRead() {
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long stamp = stampedLock.tryOptimisticRead();
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int currentValue = value;
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if (!stampedLock.validate(stamp)) { // 检查写冲突<sup>8</sup>
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stamp = stampedLock.readLock(); // 降级为悲观读
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try {
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currentValue = value;
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} finally {
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stampedLock.unlockRead(stamp);
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}
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}
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return currentValue;
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}
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// 写操作（独占）
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public void writeValue(int newValue) {
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long stamp = stampedLock.writeLock();
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try {
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value = newValue;
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} finally {
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stampedLock.unlockWrite(stamp);
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}
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}
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}
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```
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优势：
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乐观读性能比传统读锁高30%+（读多写少场景）8
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支持锁升级（读锁→写锁）8
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避免写线程饥饿问题8
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## 推荐选择：
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优先使用ReentrantReadWriteLock：常规读写分离需求35
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选择StampedLock：读操作占比超过90%的高并发场景8
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避免使用synchronized：除非并发量极低
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@@ -142,3 +142,9 @@
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>
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> 入门小站。https://rumenz.com/
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> BestJavaer。https://github.com/crisxuan/bestJavaer
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> 2024年12月23日
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> 计划中的项目
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> * BestJavaer java-basic java-concurrency jvm https://github.com/crisxuan/bestJavaer/tree/master
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> * 书籍 《Java编程思想》 《Java核心技术卷》《Java并发编程实践》
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> * 源码 https://github.com/coderbruis/JavaSourceCodeLearning/blob/master/note/JDK https://github.com/seaswalker/jdk-sourcecode-analysis/blob/master/README.md
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