Java多線程-新特徵-鎖

Java中讀寫鎖有個接口java.util.concurrent.locks.ReadWriteLock，也有具體的實現ReentrantReadWriteLock，詳細的API能夠查看JavaAPI文檔。

下面這個例子是在文例子的基礎上，將普通鎖改成讀寫鎖，並添加帳戶餘額查詢的功能，代碼以下：

package cn.thread; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; /** * 讀寫鎖 * * @author 林計欽 * @version 1.0 2013-7-25 上午10:33:37 */ public class WriteReadLockTest { public static void main(String[] args) { WriteReadLockTest test = new WriteReadLockTest(); // 建立併發訪問的帳戶 MyCount myCount = test.new MyCount("95599200901215522", 10000); // 建立一個鎖對象 ReadWriteLock lock = new ReentrantReadWriteLock(false); // 建立一個線程池 ExecutorService pool = Executors.newFixedThreadPool(2); // 建立一些併發訪問用戶，一個信用卡，存的存，取的取，好熱鬧啊 User u1 = test.new User("張三", myCount, -4000, lock, false); User u2 = test.new User("張三他爹", myCount, 6000, lock, false); User u3 = test.new User("張三他弟", myCount, -8000, lock, false); User u4 = test.new User("張三", myCount, 800, lock, false); User u5 = test.new User("張三他爹", myCount, 0, lock, true); // 在線程池中執行各個用戶的操做  pool.execute(u1); pool.execute(u2); pool.execute(u3); pool.execute(u4); pool.execute(u5); // 關閉線程池  pool.shutdown(); } /** * 信用卡的用戶 */ class User implements Runnable { private String name; // 用戶名 private MyCount myCount; // 所要操做的帳戶 private int iocash; // 操做的金額，固然有正負之分了 private ReadWriteLock myLock; // 執行操做所需的鎖對象 private boolean ischeck; // 是否查詢  User(String name, MyCount myCount, int iocash, ReadWriteLock myLock, boolean ischeck) { this.name = name; this.myCount = myCount; this.iocash = iocash; this.myLock = myLock; this.ischeck = ischeck; } public void run() { if (ischeck) { // 獲取讀鎖  myLock.readLock().lock(); System.out.println("讀：" + name + "正在查詢" + myCount + "帳戶，當前金額爲" + myCount.getCash()); // 釋放讀鎖  myLock.readLock().unlock(); } else { // 獲取寫鎖  myLock.writeLock().lock(); // 執行現金業務 System.out.println("寫：" + name + "正在操做" + myCount + "帳戶，金額爲" + iocash + "，當前金額爲" + myCount.getCash()); myCount.setCash(myCount.getCash() + iocash); System.out.println("寫：" + name + "操做" + myCount + "帳戶成功，金額爲" + iocash + "，當前金額爲" + myCount.getCash()); // 釋放寫鎖  myLock.writeLock().unlock(); } } } /** * 信用卡帳戶，可隨意透支 */ class MyCount { private String oid; // 帳號 private int cash; // 帳戶餘額  MyCount(String oid, int cash) { this.oid = oid; this.cash = cash; } public String getOid() { return oid; } public void setOid(String oid) { this.oid = oid; } public int getCash() { return cash; } public void setCash(int cash) { this.cash = cash; } @Override public String toString() { return "MyCount{" + "oid='" + oid + '\'' + ", cash=" + cash + '}'; } } }

寫：張三正在操做MyCount{oid='95599200901215522', cash=10000}帳戶，金額爲-4000，當前金額爲10000
寫：張三操做MyCount{oid='95599200901215522', cash=6000}帳戶成功，金額爲-4000，當前金額爲6000 寫：張三他爹正在操做MyCount{oid='95599200901215522', cash=6000}帳戶，金額爲6000，當前金額爲6000 寫：張三他爹操做MyCount{oid='95599200901215522', cash=12000}帳戶成功，金額爲6000，當前金額爲12000 寫：張三正在操做MyCount{oid='95599200901215522', cash=12000}帳戶，金額爲800，當前金額爲12000 寫：張三操做MyCount{oid='95599200901215522', cash=12800}帳戶成功，金額爲800，當前金額爲12800 寫：張三他弟正在操做MyCount{oid='95599200901215522', cash=12800}帳戶，金額爲-8000，當前金額爲12800 寫：張三他弟操做MyCount{oid='95599200901215522', cash=4800}帳戶成功，金額爲-8000，當前金額爲4800 讀：張三他爹正在查詢MyCount{oid='95599200901215522', cash=4800}帳戶，當前金額爲4800

在實際開發中，最好在能用讀寫鎖的狀況下使用讀寫鎖，而不要用普通鎖，以求更好的性能。