Usage scenario of copyonwritearraylist

1. It is suitable for scenarios with small amount of data , It is not suitable for scenes with large amount of data . Because when writing , Array to be copied , Memory consumption , If there are many contents in the original array , May lead to young gc perhaps full gc
2. It is suitable for reading more and writing less , Not suitable for real-time reading .

CopyOnWriteArrayList It can ensure the thread safety of write operation , It can also ensure the final consistency of the data , But the real-time consistency of data cannot be guaranteed .

CopyOnWriteArrayList In write operation , Used ReentrantLock Lock to ensure thread safety , And replace the original array attribute ; But when reading, read directly array, It may happen when the write operation is replaced array Before and after . This will lead to reading old data , Cause inconsistency .

1、 If the write operation is not completed , Then read the data of the original array directly ;
2、 If the write operation is complete , But the reference has not yet pointed to the new array , So it's also reading the original array data ;
3、 If the write operation is complete , And the reference already points to the new array , So read the data directly from the new array .