synchronized及JUC显式locks 使用原理解析

// 支持中断的API
void lockInterruptibly() throws InterruptedException;
// 支持超时的API
boolean tryLock(long time, TimeUnit unit)  throws InterruptedException;
// 支持非阻塞获取锁的API
boolean tryLock();

//线程加入此条件变量的等待队列；类似Object.wait()；使用时也要放到while循环体内。
java.util.concurrent.locks.Condition#await()
java.util.concurrent.locks.Condition#awaitUninterruptibly()
java.util.concurrent.locks.Condition#awaitNanos()
java.util.concurrent.locks.Condition#await(long, java.util.concurrent.TimeUnit)
java.util.concurrent.locks.Condition#awaitUntil()
//激活此条件变量中的一个线程;类似Object.notify()
java.util.concurrent.locks.Condition#signal()
//激活此条件变量中的所有线程;类似Object.notifyAll()
java.util.concurrent.locks.Condition#signalAll()

class BoundedBuffer {
 final Lock lock = new ReentrantLock();
 final Condition notFull  = lock.newCondition();
 final Condition notEmpty = lock.newCondition();
 final Object[] items = new Object[100];
 int putptr, takeptr, count;
 public void put(Object x) throws InterruptedException {
   lock.lock();
   try {
     while (count == items.length)
       notFull.await();
     items[putptr] = x;
     if (++putptr == items.length) putptr = 0;
     ++count;
     notEmpty.signal();
   } finally {
     lock.unlock();
   }
 }
 public Object take() throws InterruptedException {
   lock.lock();
   try {
     while (count == 0)
       notEmpty.await();
     Object x = items[takeptr];
     if (++takeptr == items.length) takeptr = 0;
     --count;
     notFull.signal();
     return x;
   } finally {
     lock.unlock();
   }
 }
}

 Lock l = ...;
 l.lock();
 try {
   // access the resource protected by this lock
 } finally {
   l.unlock();
 }

 Lock lock = ...;
 if (lock.tryLock()) {
   try {
     // manipulate protected state
   } finally {
     lock.unlock();
   }
 } else {
   // perform alternative actions
 }

while (XXX)
    condition.await();

 l.lock();
 try {
    ...
    while (XXX)
      condition.await();
    ...
 } finally {
   l.unlock();
 }