More about synchronization
Often, one thread is producing some data, while another thread wants to use it.
A flag variable is introduce that both threads can check.
If the data is not ready (flag is false), the consuming thread can call the method wait ( ), which causes it to be suspended until some other event occurs.
When the producing thread has some data, it can set the flag to be true and call the method notify ( ), which causes an event that will “wake up” one of the suspended threads.
If the user doesn’t get the logic right, there are possibilities for deadlock or other forms of non-progress.