java.util.concurrent.locks

Class ReentrantLock

All Implemented Interfaces: Serializable, Lock

A reentrant mutual exclusion Lock with the same basic behavior and semantics as the implicit monitor lock accessed using synchronized methods and statements, but with extended capabilities.

也就是跟synchronized设计本意类似，都是用来实现同步的，只不过ReentrantLock还有更多的功能。

A ReentrantLock is owned by the thread last successfully locking, but not yet unlocking it.

Method:

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boolean tryLock()

void lock()

void unlock()

protected Thread getOwner() 

...

ReentrantLock: synchronized

Why use a ReentrantLock if one can use synchronized(this)?

stackoverflow

A ReentrantLock is unstructured, unlike synchronized constructs – i.e. you don’t need to use a block structure for locking and can even hold a lock across methods. An example:

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private ReentrantLock lock;

public void foo() {
  ...
  lock.lock();
  ...
}

public void bar() {
  ...
  lock.unlock();
  ...
}

Aside from that, ReentrantLock supports lock polling and interruptible lock waits that support time-out. ReentrantLock also has support for configurable fairness policy, allowing more flexible thread scheduling.

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