ReentrantLock 和 synchronized 的区别：
但是要注意，lock 是有次数的，如果连续调用了两次lock，那么就需要调用两次unlock。否则的话，别的线程是拿不到锁的。
/**
* 很平常的用锁 没有感觉reentrantlocak 的强大
*
* 如果当前线程已经拿到一个锁了 那么再次调用 会里面返回true
* 当前线程的锁数量是 2个
*
*/
private void normalUse() {
ReentrantLock reentrantLock = new ReentrantLock();
new Thread("thread1"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread1 lock");
reentrantLock.lock();
reentrantLock.lock();
LogToFile.log(TAG,"thread1 getHoldCount:" + reentrantLock.getHoldCount() );
try {
LogToFile.log(TAG,"thread1 run");
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
//如果说你的线程占了两个锁 一个没有释放 其他线程都拿不到这个锁
//上面lock 了两次 这里需要unLock 两次
reentrantLock.unlock();
reentrantLock.unlock();
LogToFile.log(TAG,"thread1 unlock");
}
}.start();
new Thread("thread2"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread2 lock");
reentrantLock.lock();
LogToFile.log(TAG,"thread2 run");
reentrantLock.unlock();
LogToFile.log(TAG,"thread2 unlock");
}
}.start();
}
ReentrantLock trylock 会尝试去拿锁，如果拿得到，就返回true, 如果拿不到就返回false.这个都是立马返回，不会阻塞线程。
如果当前线程已经拿到锁了，那么trylock 会返回true.
/**
* trylock 不管能不能拿到锁 都会里面返回结果 而不是等待
* tryLock 会破坏ReentrantLock 的 公平机制
* 注意 如果没有拿到锁 执行完代码之后不要释放锁，
* 否则会有exception
*
*/
private void UseTryLock() {
ReentrantLock reentrantLock = new ReentrantLock();
new Thread("thread1"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread1 lock");
reentrantLock.lock();
try {
LogToFile.log(TAG,"thread1 run");
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
reentrantLock.unlock();
LogToFile.log(TAG,"thread1 unlock");
}
}.start();
new Thread("thread2"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread2 tryLock");
boolean success = reentrantLock.tryLock();
LogToFile.log(TAG,"thread2 run");
if (success) {
reentrantLock.unlock();
LogToFile.log(TAG,"thread2 unlock");
// java.lang.IllegalMonitorStateException
// at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:123)
// at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1235)
// at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:429)
}
}
}.start();
}
ReentrantLock 可以指定，尝试去获取锁，等待多长时间之后，如果还获取不到，那么就放弃。
/**
* tryLock(5, TimeUnit.SECONDS)
* 如果5s之后 还拿不到锁 那么就不再堵塞线程，也不去拿锁了 执行执行下面的代码了
*/
private void UseTryLockWhitTime() {
ReentrantLock reentrantLock = new ReentrantLock();
new Thread("thread1"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread1 lock");
reentrantLock.lock();
try {
LogToFile.log(TAG,"thread1 run");
Thread.sleep(1000 * 10);
} catch (InterruptedException e) {
e.printStackTrace();
}
reentrantLock.unlock();
LogToFile.log(TAG,"thread1 unlock");
}
}.start();
new Thread("thread2"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread2 tryLock");
boolean success = false;
try {
success = reentrantLock.tryLock(5, TimeUnit.SECONDS);
LogToFile.log(TAG,"thread2 run");
if (success) {
reentrantLock.unlock();
LogToFile.log(TAG,"thread2 unlock");
// java.lang.IllegalMonitorStateException
// at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:123)
// at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1235)
// at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:429)
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
}
一旦调用了ReentrantLock .lock() ，如果你的线程被其他线程interrupt，那么你的线程并不会interrupt，而是继续等待锁。
/**
* lockInterruptibly() 和 lock 的区别是
* 如果当前线程被Interrupt 了，那么lockInterruptibly 就不再等待锁了。直接会抛出来一个异常给你处理
* 如果是lock 的话 就算 线程被其他的线程lockInterrupt 了，不管用，他还会继续等待锁
*/
private void UseLockIntercepter() {
ReentrantLock reentrantLock = new ReentrantLock();
Thread thread = new Thread("thread1") {
@Override
public void run() {
super.run();
LogToFile.log(TAG, "thread1 lock");
reentrantLock.lock();
LogToFile.log(TAG, "thread1 run");
if (reentrantLock.getHoldCount() != 0) {
reentrantLock.unlock();
}
LogToFile.log(TAG, "thread1 unlock");
}
};
new Thread("thread2"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread2 tryLock");
boolean success = false;
try {
reentrantLock.lock();
thread.start();
thread.interrupt();
success = reentrantLock.tryLock(5, TimeUnit.SECONDS);
LogToFile.log(TAG,"thread2 run");
if (success) {
reentrantLock.unlock();
reentrantLock.unlock();
LogToFile.log(TAG,"thread2 unlock");
// java.lang.IllegalMonitorStateException
// at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:123)
// at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1235)
// at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:429)
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
}
如果当前线程调用lockInterruptibly 这个方法去获取锁，当其他的线程把你的线程给interrupt 之后，那么你的线程就不再等待锁了，执行下面的代码。
/**
* lockInterruptibly() 和 lock 的区别是
* 如果当前线程被Interrupt 了，那么lockInterruptibly 就不再等待锁了。直接会抛出来一个异常给你处理
* 如果是lock 的话 就算 线程被其他的线程lockInterrupt 了，不管用，他还会继续等待锁
*/
private void UseLockIntercepter2() {
ReentrantLock reentrantLock = new ReentrantLock();
Thread thread = new Thread("thread1") {
@Override
public void run() {
super.run();
LogToFile.log(TAG, "thread1 lock");
try {
reentrantLock.lockInterruptibly();
} catch (InterruptedException e) {
e.printStackTrace();
LogToFile.log(TAG, "thread1 lock InterruptedException ");
}
LogToFile.log(TAG, "thread1 run");
if (reentrantLock.getHoldCount() != 0) {
reentrantLock.unlock();
}
LogToFile.log(TAG, "thread1 unlock");
}
};
new Thread("thread2"){
@Override
public void run() {
super.run();
LogToFile.log(TAG,"thread2 tryLock");
boolean success = false;
try {
reentrantLock.lock();
thread.start();
thread.interrupt();
success = reentrantLock.tryLock(5, TimeUnit.SECONDS);
LogToFile.log(TAG,"thread2 run");
if (success) {
reentrantLock.unlock();
reentrantLock.unlock();
LogToFile.log(TAG,"thread2 unlock");
// java.lang.IllegalMonitorStateException
// at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:123)
// at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1235)
// at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:429)
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
}
condition. 的await 相当于 object 的wait 方法，就是等待其他线程唤醒，但是调用之前必须要reentrantLock.lock(); 一下，不然会抛异常。
/**
* tryLock(5, TimeUnit.SECONDS)
* 如果5s之后 还拿不到锁 那么就不再堵塞线程，也不去拿锁了 执行执行下面的代码了
*/
private void UseCondition() {
ReentrantLock reentrantLock = new ReentrantLock();
Condition condition = reentrantLock.newCondition();
Thread thread = new Thread("thread1") {
@Override
public void run() {
super.run();
try {
reentrantLock.lock();
LogToFile.log(TAG, "thread1 wait");
//await 其实是会释放锁的 其他的线程可以拿到锁 然后signal 不然的话岂不是要卡死？
condition.await();
LogToFile.log(TAG, "thread1 run");
Thread.sleep(1000 * 3);
condition.signalAll();
reentrantLock.unlock();
} catch (InterruptedException e) {
e.printStackTrace();
}
LogToFile.log(TAG, "thread1 unlock");
}
};
thread.start();
Thread thread1 = new Thread("thread2") {
@Override
public void run() {
super.run();
//调用signal 之前一定要lock
reentrantLock.lock();
//就算没有人调用await 那么signal 方法也不会有什么问题
condition.signal();
try {
LogToFile.log(TAG, "thread2 wait");
condition.await();
LogToFile.log(TAG, "thread2 run");
} catch (InterruptedException e) {
e.printStackTrace();
}
reentrantLock.unlock();
}
};
thread1.start();
}
wait 方法调用之前也要synchronized 一个锁。
/**
* 使用wait
*/
private void UseWait() {
ReentrantLock reentrantLock = new ReentrantLock();
Condition condition = reentrantLock.newCondition();
new Thread("thread1"){
@Override
public void run() {
super.run();
try {
synchronized (condition) {
LogToFile.log(TAG,"thread1 wait");
condition.wait();
}
LogToFile.log(TAG,"thread1 run");
Thread.sleep(1000 * 10);
synchronized (condition) {
condition.notifyAll();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
LogToFile.log(TAG,"thread1 unlock");
}
}.start();
new Thread("thread2"){
@Override
public void run() {
super.run();
synchronized (condition) {
condition.notify();
}
try {
LogToFile.log(TAG,"thread2 wait");
synchronized (condition){
condition.wait();
}
LogToFile.log(TAG,"thread2 run");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
}
synchronized 锁等待的线程，当被其他线程interrupt 的时候，并不会停止。
/**
* synchronized 的锁，不能被中断
*/
public void testSyncInter(){
Object lock = new Object();
Thread thread = new Thread("thread1") {
@Override
public void run() {
super.run();
synchronized (lock) {
LogToFile.log(TAG, "thread1 lock");
LogToFile.log(TAG, "thread1 run");
}
LogToFile.log(TAG, "thread1 unlock");
}
};
new Thread("thread2"){
@Override
public void run() {
super.run();
synchronized (lock) {
LogToFile.log(TAG,"thread2 start");
thread.start();
thread.interrupt();
}
LogToFile.log(TAG,"thread2 run");
}
}.start();
}
/**
* BlockingQueue 会阻塞当前的线程 等着其他线程放数据
*/
public void testArrayBlockQueue(){
BlockingQueue<Integer> blockingQueue = new ArrayBlockingQueue<>(4);
new Thread("thread1"){
@Override
public void run() {
super.run();
try {
LogToFile.log(TAG,"thread1 take");
blockingQueue.take();
LogToFile.log(TAG,"thread1 take get");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
new Thread("thread2"){
@Override
public void run() {
super.run();
try {
Thread.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}
try {
LogToFile.log(TAG,"thread2 put");
//put 会阻塞 但是add 不会
blockingQueue.put(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
}
下面的代码，可以看到ArrayBlockingQueue 创建了ReentrantLock ，以及两个condition
/** Main lock guarding all access */
final ReentrantLock lock;
/** Condition for waiting takes */
private final Condition notEmpty;
/** Condition for waiting puts */
private final Condition notFull;
public ArrayBlockingQueue(int capacity, boolean fair) {
if (capacity <= 0)
throw new IllegalArgumentException();
this.items = new Object[capacity];
lock = new ReentrantLock(fair);
notEmpty = lock.newCondition();
notFull = lock.newCondition();
}
当出队列的时候，notFull.signal(); 也就是当前的队列不是满的了，可以放元素进去了。
/**
* Inserts the specified element at the tail of this queue, waiting
* for space to become available if the queue is full.
*
* @throws InterruptedException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public void put(E e) throws InterruptedException {
checkNotNull(e);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (count == items.length)
notFull.await();
enqueue(e);
} finally {
lock.unlock();
}
}
private E dequeue() {
// assert lock.getHoldCount() == 1;
// assert items[takeIndex] != null;
final Object[] items = this.items;
@SuppressWarnings("unchecked")
E x = (E) items[takeIndex];
items[takeIndex] = null;
if (++takeIndex == items.length)
takeIndex = 0;
count--;
if (itrs != null)
itrs.elementDequeued();
notFull.signal();
return x;
}
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (count == 0)
notEmpty.await();
return dequeue();
} finally {
lock.unlock();
}
}
private void enqueue(E x) {
// assert lock.getHoldCount() == 1;
// assert items[putIndex] == null;
final Object[] items = this.items;
items[putIndex] = x;
if (++putIndex == items.length)
putIndex = 0;
count++;
notEmpty.signal();
}
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