What are some best practices or design patterns for using runnable and running threads?

1 Runnable vs Running

A runnable thread is a thread that is ready to execute, but not necessarily running on the CPU. A running thread is a thread that is actually executing on the CPU. The operating system decides which runnable threads to assign to the available CPUs, based on factors such as priority, fairness, and load balancing. Therefore, a runnable thread may have to wait for its turn to run, or may be preempted by another thread. A running thread may also be blocked by an I/O operation, a synchronization mechanism, or an exception, and become runnable again.

3 Thread Creation

One of the best practices for creating threads is to implement the Runnable interface rather than extending the Thread class. This way, you can separate the task logic from the thread management, and avoid the drawbacks of inheritance, such as tight coupling and reduced flexibility. To create a thread using the Runnable interface, you need to define a class that implements the run() method, which contains the code to execute in the thread. Then, you need to create an instance of the Runnable class and pass it to the constructor of the Thread class. Finally, you need to call the start() method on the Thread object to make it runnable.

4 Thread Pool

Another best practice for using threads is to use a thread pool rather than creating new threads for each task. A thread pool is a collection of reusable threads that can execute multiple tasks concurrently. Using a thread pool can improve the performance and scalability of your application, as it reduces the overhead of creating and destroying threads, and avoids the problems of having too many threads, such as resource contention and memory exhaustion. To use a thread pool, you need to use one of the classes in the java.util.concurrent package, such as ExecutorService, ThreadPoolExecutor, or ScheduledThreadPoolExecutor. These classes provide methods to submit tasks to the thread pool, manage the lifecycle of the threads, and handle the exceptions and results of the tasks.

5 Thread Safety

One of the most challenging aspects of using threads is ensuring thread safety, which means that your code behaves correctly when accessed by multiple threads concurrently. Thread safety can be violated by race conditions, which occur when the outcome of an operation depends on the timing or order of execution of the threads. To prevent race conditions, you need to synchronize the access to the shared data or resources, using mechanisms such as locks, monitors, semaphores, or atomic variables. Synchronization ensures that only one thread can access the critical section at a time, and that the changes made by one thread are visible to the others. However, synchronization also introduces some costs and risks, such as performance degradation, deadlock, livelock, or starvation. Therefore, you need to use synchronization judiciously, following principles such as minimizing the scope and duration of the critical section, avoiding nested locks, and favoring immutable or thread-local data.

6 Thread Communication

Another important aspect of using threads is thread communication, which means that your threads can coordinate their actions and exchange information. Thread communication can be achieved by using shared variables, signals, or messages. Shared variables are the simplest form of communication, but they require synchronization to ensure consistency and visibility. Signals are mechanisms that allow one thread to notify another thread about a specific event, such as interrupting, joining, or waiting. Messages are objects that contain data or instructions that are sent and received by threads, using queues, pipes, or sockets. Messages are more decoupled and scalable than shared variables or signals, but they also require more complexity and overhead.