Why Wait () and notify () must use sychronized

Why Wait () and notify () must use sychronized

If not, will error illegalmonitorstateexception. first, it is clear that the implementation basis for Wait () and notify () is based on the existence of objects. So why is it based on object existence?

Here to be clear, waiting is a signal sent by an object, so to exist based on the object.

Since it is object-based, it has to use a data structure to hold these waiting threads, and the data structure should be bound to that object, at which point there may be multiple threads calling the Wait ()/notify () method.

When writing and deleting data in a doubly linked list to this object, there is still a concurrency problem, which in theory requires a lock to control. In the JVM kernel source code does not discover any oneself to use the lock to control writes the action, only by checking whether the current thread is the object owner to determine whether to throw the corresponding exception. This shows that it wants the action to be controlled by the abstraction level of the Java program, why it does not want to control the lock itself.

Because sometimes a lower level of abstraction is not necessarily a good thing, because such requests may be recycled over and over again, or the code might be reused elsewhere, perhaps it would be better to be coarse-grained, and such code would be clearer in the Java program itself. It is easier to see the relationship between each other.