Learn about the best practices for concurrency in Java to ensure your multi-threaded applications are efficient, synchronized, and error-free.

The ReentrantLock class is part of the java.util.concurrent.locks package. It implements the Lock interface, which defines the basic operations of a lock: lock, unlock, tryLock, and lockInterruptibly.

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在Java中，synchronized关键字也可用来实现可重入锁。 在Java6以前，ReentrantLock的性能远好于synchronized关键字，在Java6以后JVM对synchronized关键字进行了大幅度的优化，现在两者性能几乎差不多。 另外，ReentrantLock大部分是纯Java代码实现的，而synchronized是由JVM内部实现的。

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事实上，Lock 是 java.util.concurrent.locks包 下的接口，Lock 实现提供了比 synchronized 关键字 更广泛的锁操作，它能以更优雅的方式处理线程同步问题。

2）采用synchronized方式不需要用户去手动释放锁，当synchronized方法或者synchronized代码块执行完之后，系统会自动让线程释放对锁的占用；而 Lock则必须要用户去手动释放锁，如果没有主动释放锁，就有可能导致死锁现象。 二. java.util.concurrent.locks包下常用的类与接口 ...

几天前，当我诊断一些 JIT 编译期间奇怪的分配问题时，发现 java.util.concurrent.locks.ReentrantLock 的分配有问题，不过这只在竞争条件下出现。（这一点很容易证明，只要运行一个在 Lock 上建立竞争并指定 –verbosegc 参数测试程序（类似下面的程序））。

The java.util.concurrent.locks subpackage contains low-level utility types for locking and waiting for conditions, which are different from using Java’s low-level synchronization and monitors.