ThreadLocal源代码2
2024-09-02 07:23:59
private static int nextIndex(int i, int len) {
return ((i + 1 < len) ? i + 1 : 0);
}
private static int prevIndex(int i, int len) {
return ((i - 1 >= 0) ? i - 1 : len - 1);
}
ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
try {
threadLocal.set(new Session(1, "Misout的博客"));
// 其它业务逻辑
} finally {
threadLocal.remove();
}
//还记得Hibernate的session获取场景吗？
private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
//获取Session
public static Session getCurrentSession(){
Session session = threadLocal.get();
//判断Session是否为空，如果为空，将创建一个session，并设置到本地线程变量中
try {
if(session ==null&&!session.isOpen()){
if(sessionFactory==null){
rbuildSessionFactory();// 创建Hibernate的SessionFactory
}else{
session = sessionFactory.openSession();
}
}
threadLocal.set(session);
} catch (Exception e) {
// TODO: handle exception
} return session;
}
public class MultiThreadDemo {
public static void main(String[] args) throws InterruptedException {
private int value = 0;
Thread increaseThread = new Thread(new Runnable() {
@Override
public void run() {
try {
value = 10;
Thread.sleep(10);
System.out.println("increase value: " + value);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
Thread decreaseThread = new Thread(new Runnable() {
@Override
public void run() {
try {
value = -10;
Thread.sleep(10);
System.out.println("decrease value: " + value);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
increaseThread.start();
decreaseThread.start();
}
}
public class SimpleImpl {
public static void main(String[] args) throws InterruptedException {
private Map<Long, Integer> cacheMap = new HashMap<>();
private int defaultValue = 0 ;
Thread increaseThread = new Thread(new Runnable() {
@Override
public void run() {
long id = Thread.currentThread().getId();
cacheMap.put(id, 10);
Thread.sleep(10);
long id = Thread.currentThread().getId();
if (cacheMap.containsKey(id)) {
return cacheMap.get(id);
}
return defaultValue;
}
});
Thread decreaseThread = new Thread(new Runnable() {
@Override
public void run() {
long id = Thread.currentThread().getId();
cacheMap.put(id, -10);
Thread.sleep(10);
long id = Thread.currentThread().getId();
if (cacheMap.containsKey(id)) {
return cacheMap.get(id);
}
return defaultValue;
}
});
increaseThread.start();
decreaseThread.start();
}
}
public class SimpleImpl2 {
public static class CommonThread extends Thread {
Map<Integer, Integer> cacheMap = new HashMap<>();
}
public static class Number {
public void increase() throws InterruptedException {
Integer id = this.hashCode();
Map<Integer, Integer> cacheMap = (CommonThread) Thread.currentThread().cacheMap;
cacheMap.put(id, 10);
Thread.sleep(10);
return cacheMap.get(id);
}
public void decrease() throws InterruptedException {
Integer id = this.hashCode();
Map<Integer, Integer> cacheMap = (CommonThread) Thread.currentThread().cacheMap;
cacheMap.put(id, -10);
Thread.sleep(10);
return cacheMap.get(id);
}
}
public static void main(String[] args) throws InterruptedException {
final Number number = new Number();
Thread increaseThread = new CommonThread() {
@Override
public void run() {
number.increase();
}
};
Thread decreaseThread = new CommonThread() {
@Override
public void run() {
number.decrease();
}
};
increaseThread.start();
decreaseThread.start();
}
}
在上面的实现中，当线程消亡之后，线程中 cacheMap 也会被回收，它当中存放的副本变量（value）也会被全部回收，并且 cacheMap 是线程私有的，不会出现多个线程同时访问一个 cacheMap 的情况。在 Java 中，ThreadLocal 类的实现就是采用的这种思想，注意只是思想，实际的实现和上面的并不一样。
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