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ReentrantLock ?????????

ReentrantLock ? Java ?????????????????????????????????????????????????????????? AbstractQueuedSynchronizer (AQS) ?????CAS??????????????????

1. ??

ReentrantLock ??? Lock ?????? lock() ? unlock() ?????? newCondition() ????????????????????????????????????????????

2. ????

ReentrantLock ????????Sync?NonfairSync ? FairSync????NonfairSync ? FairSync ??? Sync?Sync ???? AbstractQueuedSynchronizer?

2.1 Sync ?

Sync ?? ReentrantLock ???????????????????????? nonfairTryAcquire()?tryRelease() ??

nonfairTryAcquire()

• ????????????????
• ????????state == 0????? CAS ??????
• ????????????????????
• ????????? false?

tryRelease()

• ????????????????
• ????????????? IllegalMonitorStateException?
• ???????????????????
• ???????????????

2.2 NonfairSync ?

NonfairSync ????????????????????? lock() ???? CAS ???????????????????????

acquire()

• ??? nonfairTryAcquire() ????
• ???????????????

addWaiter()

• ???????????????
• ?? CAS ???????????

acquireQueued()

• ??????????????
• ?????????? SIGNAL???????
• ??????????????????

2.3 FairSync ?

FairSync ?????????? lock() ???? acquire(1) ????????????????????????????????????????????????

3. ????

3.1 ?????

public class TestReentrantLock {    private static Lock lock = new ReentrantLock();    public static void main(String[] args) {        MyThread t1 = new MyThread("t1", lock);        MyThread t2 = new MyThread("t2", lock);        MyThread t3 = new MyThread("t3", lock);        t1.start();        t2.start();        t3.start();    }    static class MyThread extends Thread {        private Lock lock;        MyThread(String name, Lock lock) {            super(name);            this.lock = lock;        }        public void run() {            lock.lock();            try {                System.out.println(Thread.currentThread().getName() + " running");                Thread.sleep(500);            } catch (InterruptedException e) {                e.printStackTrace();            } finally {                lock.unlock();            }        }    }}

3.2 ????

????????????????????????????????????

?????????????? ReentrantLock ?????????????????????

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