package com.sinata.rest.common.lock;
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import java.util.concurrent.ConcurrentHashMap;
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import java.util.concurrent.ExecutorService;
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import java.util.concurrent.Executors;
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public class IdLocker {
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public static Object simpleLock(Integer id) {
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return id.toString().intern();
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}
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private ConcurrentHashMap<Integer, IdLock> locks = new ConcurrentHashMap<>();
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public IdLock acquireLock(Integer userId) {
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IdLock lock = locks.get(userId);
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if (lock == null) {
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synchronized (this) {
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lock = locks.get(userId);
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if (lock == null) {
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lock = new IdLock(userId);
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locks.put(userId, lock);
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}
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}
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}
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synchronized (lock) {
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//如果是初始值，则设置为1，表示当前获得锁的数量为1
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if (lock.count.get() == Integer.MAX_VALUE) {
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lock.count.set(1);
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} else {
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//当数量不为0，标识锁还有效
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if (lock.count.get() != 0) {
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//获得锁的将持有者数量加1
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lock.count.addAndGet(1);
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}
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}
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}
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//当数量为0，标识锁已经被弃用，需要重新创建并获得
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if (lock.count.get() == 0) {
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return acquireLock(userId);
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}
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return lock;
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}
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public void locked(Integer id, Runnable runnable) {
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IdLock lock = acquireLock(id);
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try {
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synchronized (lock) {
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runnable.run();
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}
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releaseLock(lock);
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} catch (Exception e) {
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releaseLock(lock);
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throw e;
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}
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}
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public void releaseLock(IdLock lock) {
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//用完锁要释放,内存
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synchronized (lock) {
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lock.count.getAndAdd(-1);
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if (lock.count.get() == 0) {
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synchronized (this) {
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locks.remove(lock.getId());
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}
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}
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}
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}
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static class TestHolder {
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int count = 0;
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}
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public static void main(String[] args) {
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System.out.println("Printer");
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TestHolder countA = new TestHolder();
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TestHolder countB = new TestHolder();
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int idA = 3;
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int idB = 4;
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IdLocker locker = new IdLocker();
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ExecutorService executor = Executors.newCachedThreadPool();
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for (int i = 0; i < 50000; i++) {
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executor.execute(() -> {
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IdLock lock = locker.acquireLock(idA);
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synchronized (lock) {
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countA.count++;
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}
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locker.releaseLock(lock);
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});
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if (i < 50) {
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new Thread(() -> {
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IdLock lock = locker.acquireLock(idA);
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synchronized (lock) {
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countA.count++;
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}
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locker.releaseLock(lock);
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}).start();
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}
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}
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for (int i = 0; i < 70000; i++) {
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executor.execute(() -> {
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IdLock lock = locker.acquireLock(idB);
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synchronized (lock) {
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countB.count++;
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}
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locker.releaseLock(lock);
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});
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}
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try {
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Thread.sleep(5000);
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System.out.println("A = " + countA.count);
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System.out.println("B = " + countB.count);
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System.out.println("Locker = " + locker.locks.size());
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executor.shutdown();
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} catch (Exception e) {
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}
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}
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}
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