notifyAll

notifyAll is a method found in many object-oriented programming languages, particularly those that support concurrency and multithreading like Java. Its primary purpose is to wake up all threads that are currently waiting on the object's monitor.

When a thread calls a method like wait() on an object, it releases the lock on that object and enters a waiting state. Other threads can then acquire the lock and potentially make changes to the object's state. If those changes are significant, a waiting thread might need to be notified that the conditions it was waiting for may have changed.

The notifyAll() method is invoked on an object by a thread that has acquired the object's lock. Once called, all threads that are currently in a wait() state on that specific object are awakened. These awakened threads will then attempt to re-acquire the object's lock. It is important to note that only one thread can hold the lock at a time. Therefore, the awakened threads will typically compete to regain the lock and resume their execution.

Compared to notify(), which wakes up only one waiting thread, notifyAll() is often considered safer and less prone to deadlock scenarios. While notify() might wake up a thread that cannot yet proceed, notifyAll() ensures that all potentially eligible threads are given a chance to re-evaluate their conditions. However, notifyAll() can also lead to increased contention if many threads are waiting, as they all race to re-acquire the lock. The choice between notify() and notifyAll() depends on the specific synchronization requirements of the application.