Detailed explanation of Java thread pool: from beginner to proficient

Java Thread pool is a resource pool used to manage and reuse threads. It provides a unified mechanism for creating, destroying and managing threads, helping developers improve application performance and simplify concurrent programming.

advantage

• Improve performance: Thread pools can save the overhead of creating and destroying threads, especially in applications that require frequent creation and destruction of threads.
• ControlConcurrency: By setting the size of the thread pool, you can control the number of threads executing simultaneously in the application to prevent too many threads from competing for resources.
• FaultSafety: When an exception occurs in a thread in the thread pool, the thread pool will automatically handle and recover to ensure the seamless operation of the application.

Main components

• Executor: Executor is the main interface of the thread pool. It provides a set of methods for creating, submitting and managing tasks.
• ThreadPoolExecutor: ThreadPoolExecutor is an implementation of the Executor interface, which provides control over thread pool size, thread creation strategy, task queue and other features.
• Task Queue: The task queue is used to store unexecuted tasks submitted to the thread pool. Task queues can be bounded (fixed size) or unbounded (unlimited size).
• Thread Factory: The thread factory is used to create threads in the thread pool. It provides options for customizing thread creation strategies and properties.

working principle

1. When an application submits a task to the thread pool, the task is added to the task queue.
2. The thread pool will create new threads or reuse existing threads to perform tasks based on the size of the thread pool and the thread creation policy.
3. After the thread executes the task, the task will be marked as completed and removed from the queue.
4. If there are no available threads in the thread pool, the task will wait until there are available threads.

Thread pool type

Java provides three main types of thread pools:

• Fixed size thread pool: Create a fixed number of threads and always maintain the same number of threads.
• Cache Thread Pool: Creates an unlimited number of threads, retains them when they are idle, and destroys them otherwise.
• Single thread pool: Use only one thread to perform tasks.

Create thread pool

Thread pools can be created through the Executors class:

ThreadPoolExecutor executor = new ThreadPoolExecutor(
corePoolSize, // Thread pool core size
maximumPoolSize, // Maximum size of thread pool
keepAliveTime, // idle thread survival time
TimeUnit.SECONDS, // Survival time unit
new ArrayBlockingQueue<>(queueSize), // task queue
new DefaultThreadFactory() // Thread factory
);

Task submission

You can call Executor's submit() or execute() method to submit the task:

executor.submit(() -> {
//task code
});

Task Management

The thread pool provides a variety of methods for managing tasks, such as:

• shutdown(): Close the thread pool and no longer accept new tasks.
• shutdownNow(): Stop the thread pool immediately and interrupt all executing tasks.
• awaitTermination(): Wait for the thread pool to terminate.

Best Practices

• Choose the correct thread pool type: Choose the most appropriate thread pool type based on the specific requirements of the application.
• Set a reasonable thread pool size: The thread pool size should be determined based on the concurrency requirements of the application and system resources.
• Using task queues: Task queues help prevent applications from causing dead locks or memory leaks due to excessive concurrency.
• Monitor the thread pool: Use Java Management Extensions (JMX) or other tools to monitor the health of the thread pool.
• Handling Exceptions: Implement a custom exception handler to handle exceptions that occur during thread execution.

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