Java中悲觀鎖和樂觀鎖分別通過不同的方法來實(shí)現(xiàn)。
悲觀鎖通常通過synchronized關(guān)鍵字或者ReentrantLock類來實(shí)現(xiàn)。使用悲觀鎖時(shí),線程獲取鎖之后會(huì)阻塞其他線程的訪問,直到當(dāng)前線程釋放鎖。悲觀鎖的實(shí)現(xiàn)方法如下:
synchronized (lockObject) {
// 被保護(hù)的臨界區(qū)
}
ReentrantLock lock = new ReentrantLock();
lock.lock();
try {
// 被保護(hù)的臨界區(qū)
} finally {
lock.unlock();
}
樂觀鎖通常通過CAS(Compare and Swap)操作或者版本號(hào)控制來實(shí)現(xiàn)。使用樂觀鎖時(shí),線程不會(huì)阻塞,而是通過比較當(dāng)前值和預(yù)期值的方式來判斷是否可以進(jìn)行更新操作。樂觀鎖的實(shí)現(xiàn)方法如下:
AtomicInteger value = new AtomicInteger();
int expect = value.get();
int update = expect + 1;
while (!value.compareAndSet(expect, update)) {
expect = value.get();
update = expect + 1;
}
class OptimisticLock {
private int version = 0;
private Object data;
public synchronized boolean update(Object newData, int currentVersion) {
if (currentVersion == version) {
this.data = newData;
this.version++;
return true;
}
return false;
}
}