CopyOnWriteArrayList details

Background:

ArrayList is not thread-safe. Although Collections.SynchronizedList is thread-safe, it simply adds a Synchronized synchronization block to all methods, so thatAlthough it can guarantee thread safety, it means that only one thread can operate the list at the same time, and the concurrency efficiency is low.

Collections.SynchronizedList is at best a thread-safe container, not a concurrent container.Therefore, we have today's protagonist: CopyOnWriteArrayList.

CopyOnWriteArrayList specific implementation

CopyOnWriteArrayList is an ArrayList that uses the CopyOnWrite mechanism, which is the copy-on-write mechanism.To put it simply, when reading, it is the same as ordinary ArrayList. When writing, it needs to be locked. In the locked synchronization block, the original array is copied to a new array, and the new array is added or deleted.After the specified value, finally change the pointer of the reference array in CopyOnWriteArrayList.