Multithreading and Concurrency Thread communication (wait, notify, notifyAll)

In Java, thread communication is used to coordinate the activities of multiple threads. Thread communication allows threads to send signals to each other, which can be used to coordinate access to shared resources. The `wait`, `notify`, and `notifyAll` methods are used for thread communication in Java. Here are some basics of thread communication in Java:

1. The `wait` method: The `wait` method is used to make a thread wait for a signal from another thread. The `wait` method can be called on an object that is being synchronized on. For example:

synchronized (sharedObject) {
    while (!condition) {
        sharedObject.wait();
    }
}

Here, a thread is waiting for a condition to be true. The `wait` method is called on the `sharedObject`, which ensures that the thread is waiting while holding the lock on the object.

2. The `notify` method: The `notify` method is used to wake up a thread that is waiting on an object. The `notify` method can be called on an object that is being synchronized on. For example:

synchronized (sharedObject) {
    condition = true;
    sharedObject.notify();
}

Here, the `condition` is set to true, and the `notify` method is called on the `sharedObject`, which wakes up any thread that is waiting on the object.

3. The `notifyAll` method: The `notifyAll` method is similar to the `notify` method, but it wakes up all threads that are waiting on an object. The `notifyAll` method can be called on an object that is being synchronized on. For example:

synchronized (sharedObject) {
    condition = true;
    sharedObject.notifyAll();
}

Here, the `condition` is set to true, and the `notifyAll` method is called on the `sharedObject`, which wakes up all threads that are waiting on the object.

4. The `wait` loop: When using the `wait` method, it is important to use a `while` loop to check for the condition being waited on. For example:

synchronized (sharedObject) {
    while (!condition) {
        sharedObject.wait();
    }
}

Here, the `while` loop ensures that the thread waits until the condition is true. If the `wait` method returns without the condition being true, the thread may have been woken up by a spurious wakeup.

Thread communication is an important concept in Java that allows threads to coordinate their activities and access to shared resources. By understanding the basics of thread communication, you can write more efficient and effective code that can handle complex tasks and improve performance in your applications.