Figure countdownlatch and cyclicbarrier based on AQS queue

CountDownLatch

CountDownLatch be based on AQS Sharing mode implementation

Simple to fit

CountDownLatch  be based on  AQS  The use of Shared patterns 
new CountDownLatch( Number of threads );
 Initialize the corresponding thread  
 Each child thread run Method call  countDownLatch.countDown();
 Finally, the main thread calls  countDownLatch.await();

 Realization effect :  The main thread will wait for all child threads to finish executing before proceeding 

countDownLatch.countDown()

countDownLatch.countDown()  Method will bring AQS Of status -1 
 At this time, the sub thread will status After value changes, there is no sleep  
 It will continue to execute other logic of the following sub threads (countDown Methods are usually placed at the end of the sub thread execution logic ,
 If it is placed in the front, it will cause the main thread to execute logic before the sub thread , That leads to countDownLatch invalid )

countDownLatch.await()

countDownLatch.await()  Method first judge status Reduced to  0  No, I have been blocking my sleep and waiting 
 When all child threads call  countDownLatch.countDown()  The last child thread wakes up the main thread 

CyclicBarrier

CyclicBarrier be based on Condition and ReenTrantLock Realization

Warm up scenario

CountDownLatch There are several problems ： First CountDownLatch stay await Then you have to rely on other threads to give it countDown, Open the latch ;
 secondly CountDownLatch stay countDown To 0 after , The CountDownLatch The life cycle of , It cannot be reused .
 So is there something that you can unlock yourself and reuse , yes , we have , That's it CyclicBarrier, Loop fence 

 There is a count variable  parties 
CyclicBarrier Generally speaking, the use of is 
 There is a fence  CyclicBarrier , It must be n（parties） Individuals can be pushed to 
 Later here n personal （ Threads ） To come out 
 After coming out , The fence can be used again （ reusing ）

Simple to fit

new CyclicBarrier ( Number of threads , The task executed by the main thread after all the sub threads are executed );
 Initialize the corresponding thread  
 Each child thread run Method call cyclicBarrier.await();

 Realization effect :  All child threads execute to the same wait point ,  And waiting points can be reused 

CyclicBarrier attribute

lock（ReentrantLock） It is used to give CyclicBarrier The operation is locked 
trip（Condition） Used to implement CyclicBarrier Of wait and notify Of 
parties（int） Count value , amount to CountDownLatch Of count
barrierCommand（Runnable） When CyclicBarrier After opening , Tasks to perform 
generation（Generation）CyclicBarrier Generation of , Used to implement CyclicBarrier Reuse of 
count（int） The value is equal to parties, Every time a thread enters ,count Minus one , Reduced to 0 When CyclicBarrier open , And then count Value by reset by parties

a key dowait The source code to share