Code examples explain the difference between [reentrant lock] and [non reentrant lock]?

First of all, we need to understand the concept of lock , In a multithreaded scenario , Running different threads together will lead to dirty data , To ensure thread safety , At this time, the concept of lock appears , Locks can be applied to code blocks , resources , Object lock , After locking , Only one thread is allowed to operate on it , Other threads will enter the blocking state , This is the blocking and locking method , Until the lock is released , Only other threads can acquire locks and operate on them .

The previous article focused on introducing Synchronized and Reentrantlock, Students who don't understand can have a look first ：

currentHashMap The fair lock of , Interruptible response , Restrict waiting instances

This article mainly introduces reentrant locks and non reentrant locks , stay jdk in synchronized and Reentrantlock, Are reentrant locks , For more efficient performance and deadlock prevention .

Reentrant lock can be understood as ： Under the same thread , After the outer method is locked , The method called by the inner layer can also obtain the lock normally .

Now let's introduce the code to 【 Do not reenter the lock 】 The understanding of the .

When testA() Method to obtain the lock , Call... In the business testB(), At this time because A The lock of is not released , therefore B Cannot get lock , Now B Our business cannot go on normally , Lead to A Nor can the lock be released normally ,A and B Method is deadlocked . This is the non reentrant lock .

What is a reentrant lock ？

Jdk The middle band is basically reentrant lock , Let's use synchronized introduces , Locking the same object after , Console printing can see ,threadA call threadB Method ,B and A Method will not deadlock , Business can continue .

We can use synchronized + wait + notify To implement a non reentrant lock , The code is as follows ：