同步访问共享的可变数据 笔记
1、一个非long或double类型的原子变量，在没有同步的情况下，不同的线程中值是不同的，不需要特意地做同步操作。
2、如果原子变量（非long或double类型）需要在线程间保持通讯，则可以使用两种方法：
public class StopThread {//backgroundThread?线程读取不到主线程中stopRequested变量的变化
??? private static boolean stopRequested;
??? public static void main(String[] args)
??????????? throws InterruptedException {
??????? Thread backgroundThread = new Thread(new Runnable() {
??????????? public void run() {
??????????????? int i = 0;
??????????????? while (!stopRequested)
??????????????????? i++;
??????????? }
??????? });
??????? backgroundThread.start();
??????? TimeUnit.SECONDS.sleep(1);
??????? stopRequested = true;
??? }
?}
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a、使用同步的方法，如果只是要求线程间通讯，没必要这样；如果这样做了，就要求set,get都要用上同步修饰符，否则达不到效果
public class StopThread {
??? private static boolean stopRequested;
??? private static synchronized void requestStop() {//set
??????? stopRequested = true;
??? }
??? private static synchronized boolean stopRequested() {//get
??????? return stopRequested;
??? }
??? public static void main(String[] args)
??????????? throws InterruptedException {
??????? Thread backgroundThread = new Thread(new Runnable() {
??????????? public void run() {
??????????????? int i = 0;
??????????????? while (!stopRequested())
??????????????????? i++;
??????????? }
??????? });
??????? backgroundThread.start();
??????? TimeUnit.SECONDS.sleep(1);
??????? requestStop();
??? }
}
b、volitile修饰符不执行互斥访问，但可以使任何线程可以读取到最新写入的值
public class StopThread {
??? private static volatile boolean stopRequested;
??? public static void main(String[] args)
??????????? throws InterruptedException {
??????? Thread backgroundThread = new Thread(new Runnable() {
??????????? public void run() {
??????????????? int i = 0;
??????????????? while (!stopRequested)
??????????????????? i++;
??????????? }
??????? });
??????? backgroundThread.start();
??????? TimeUnit.SECONDS.sleep(1);
??????? stopRequested = true;
??? }
}
3、尽量将可变数据限制在单个线程中
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