Detailed explanation of common problems in Java thread pool

Thread pool is a predefined threadcollection that is made available to applications on demand. It simplifies thread handling and improves application performance and scalability by managing the creation and destruction of threads.

Why use thread pool?

Using a thread pool has the following benefits:

• Reduce the overhead of thread creation and destruction and improve performance.
• Limit ConcurrencyNumber of threads to prevent exhaustion of system resources.
• Simplify thread management and fault handling.
• Improve application scalability and easily adapt to load changes.

How to configure the thread pool correctly?

When configuring the thread pool, you need to consider the following parameters:

• Number of core threads: Minimum number of threads to always run.
• Maximum number of threads: The maximum number of threads allowed by the thread pool.
• Queue capacity: The size of the task queue waiting for thread execution.
• Thread Factory: Factory used to create threads.
• Rejection policy: How to handle new tasks when the queue is full.

common problem

How are threads in the thread pool created?

Thread pool uses thread factory to create threads. The thread factory is responsible for configuring new threads, such as name, priority, and daemon thread flags.

How to adjust the thread pool size?

The thread pool size can be dynamically adjusted through the setCorePoolSize() and setMaximumPoolSize() methods.

What happens when the queue is full?

When the queue is full, the thread pool will handle new tasks according to its rejection policy. Common rejection strategies include:

• AbortPolicy: Throws RejectedExecut<strong class="keylink">io</strong>nException.
• CallerRunsPolicy: Run the task on the calling thread.
• DiscardOldestPolicy: Discard the oldest task in the queue and then execute the new task.
• DiscardPolicy: Discard new tasks directly.

How to close the thread pool?

To shut down the thread pool, you can use the shutdown() or shutdownNow() method. shutdown() gracefully stops the thread pool, waiting for all executing tasks to complete, while shutdownNow() stops the thread pool immediately, interrupting executing tasks.

How to monitor the thread pool?

You can monitor the thread pool through various methods of the ThreadPoolExecutor class, for example:

• getPoolSize(): Get the current thread pool size.
• getActiveCount(): Get the number of threads executing tasks.
• getCompletedTaskCount(): Get the number of completed tasks.
• getQueue(): Get the task queue.

Best Practices

Best practices for using thread pools include:

Select the appropriate thread pool type (fixed number of threads,
• cachenumber of threads, single-threaded thread pool).
Correctly configure thread pool parameters according to application requirements.
Monitor the thread pool and adjust parameters as needed.
Use a reject policy to handle queue full situations.
Close the thread pool gracefully and wait for all tasks to complete.

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