ReentrantLock笔记(一)

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ReentrantLock基本使用

交替输出

ReentrantLock lock = new ReentrantLock(true);//true为公平锁，false或缺省为非公平锁 Runnable r = () -> { while (!Thread.currentThread().isInterrupted()) { lock.lock(); try { System.out.println("当前线程：" + Thread.currentThread().getName()); TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } finally { lock.unlock(); } } }; new Thread(r).start(); Thread.sleep(10); new Thread(r).start(); Thread.sleep(10); new Thread(r).start();

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生产者、消费者

ReentrantLock lock = new ReentrantLock(); LinkedList queue = new LinkedList<Object>(); Condition notEmpty = lock.newCondition(); Condition notFull = lock.newCondition(); int max = 5; new Thread(() -> { while (!Thread.currentThread().isInterrupted()) { lock.lock(); try { while (queue.isEmpty()) { try { System.out.println("消费者等待..."); notEmpty.await(); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } } queue.poll(); System.out.println("消费者消费一个，剩余：" + queue.size()); notFull.signalAll(); } finally { lock.unlock(); } try { Thread.sleep(1000); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } } }).start(); new Thread(() -> { while (!Thread.currentThread().isInterrupted()) { lock.lock(); try { while (queue.size() >= max) { try { System.out.println("生产者等待..."); notFull.await(); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } } queue.add(1); System.out.println("生产者生产一个，总数：" + queue.size()); notEmpty.signalAll(); } finally { lock.unlock(); } try { Thread.sleep(500); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } } }).start();

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自定义锁

class Mutex implements Lock, java.io.Serializable { // 内部类，自定义同步器 private static class Sync extends AbstractQueuedSynchronizer { // 是否处于占用状态 protected boolean isHeldExclusively() { return getState() == 1; } // 当状态为0的时候获取锁 public boolean tryAcquire(int acquires) { assert acquires == 1; // Otherwise unused if (compareAndSetState(0, 1)) { setExclusiveOwnerThread(Thread.currentThread()); return true; } return false; } // 释放锁，将状态设置为0 protected boolean tryRelease(int releases) { assert releases == 1; // Otherwise unused if (getState() == 0) throw new IllegalMonitorStateException(); setExclusiveOwnerThread(null); setState(0); return true; } // 返回一个Condition，每个condition都包含了一个condition队列 Condition newCondition() { return new ConditionObject(); } } // 仅需要将操作代理到Sync上即可 private final Sync sync = new Sync(); public void lock() { sync.acquire(1); } public boolean tryLock() { return sync.tryAcquire(1); } public void unlock() { sync.release(1); } public Condition newCondition() { return sync.newCondition(); } public boolean isLocked() { return sync.isHeldExclusively(); } public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); } public void lockInterruptibly() throws InterruptedException { sync.acquireInterruptibly(1); } public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException { return sync.tryAcquireNanos(1, unit.toNanos(timeout)); } }

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