Inter-thread communication refers to the techniques and mechanisms used to allow threads in a Java program to communicate and synchronize with each other. In a multi-threaded program, threads may need to coordinate their activities, exchange data or signals, and/or communicate their status or progress to other threads.
In Java, inter-thread communication is usually achieved through the use of shared objects, such as monitors, semaphores, or message queues, that are accessible to multiple threads. These objects are used to implement synchronization and mutual exclusion, so that only one thread can access the shared data or resource at a time.
Java provides several mechanisms for inter-thread communication, including:
- wait(), notify(), and notifyAll(): These methods are used to implement the classic monitor-based synchronization mechanism in Java. A thread that needs to wait for a condition to be met calls the wait() method on the shared object, and another thread that changes the state of the shared object calls the notify() or notifyAll() method to wake up the waiting thread(s).
- Semaphores: A semaphore is a synchronization mechanism that allows a fixed number of threads to access a shared resource concurrently. The semaphore maintains a count of the number of threads that can access the resource at any given time, and blocks or allows threads based on this count.
- BlockingQueue: A blocking queue is a thread-safe data structure that allows multiple producers and consumers to access a shared queue. Producers add elements to the queue, and consumers remove elements from the queue, and the queue blocks the producer or consumer threads when the queue is empty or full.
Overall, inter-thread communication is an important aspect of multi-threaded programming in Java, and it requires careful design and implementation to ensure correctness and efficiency.