Shulou(Shulou.com)06/01 Report--

This article is about what Java thread pool parameters mean. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Thread pool technology is often used in java multithreaded development. This article is a detailed explanation of the seven parameters when creating a Java thread pool.

As can be seen from the source code, the constructor of the thread pool has seven parameters.

The seven parameters are:

CorePoolSize: number of core threads.

MaximumPoolSize: maximum number of threads.

KeepAliveTime: idle thread survival time.

TimeUnit: unit of time.

BlockingQueue: thread pool task queue.

ThreadFactory: the factory where the thread is created.

RejectedExecutionHandler: reject policy.

These seven parameters will be explained below.

CorePoolSize thread pool core thread size

A minimum number of threads is maintained in the thread pool, and even if these threads deal with idle state, they are not destroyed unless allowCoreThreadTimeOut is set. The minimum number of threads here is corePoolSize.

II. Maximum number of threads in maximumPoolSize thread pool

After a task is submitted to the thread pool, it will first find out if there are any idle living threads, if so, it will be directly handed over to the idle thread for execution, and if not, it will be cached in the work queue (described later). If the work queue is full, a new thread will be created, then a task will be taken from the head of the work queue to be processed by the new thread, and the task that has just been submitted will be placed at the end of the work queue. The thread pool does not create new threads indefinitely, it has a limit on the maximum number of threads, which is specified by maximunPoolSize.

3. KeepAliveTime idle thread survival time

If a thread is idle and the current number of threads is greater than corePoolSize, the idle thread will be destroyed after the specified time, which is set by keepAliveTime

4. Unit idle thread survival time unit

The unit of measurement of keepAliveTime

5. WorkQueue work queue

After the new task is submitted, it is first entered into the work queue, and the task is removed from the queue when the task is scheduled. Four work queues are available in jdk:

① ArrayBlockingQueue

A bounded blocking queue based on the array, sorted by FIFO. When a new task comes in, it is placed at the end of the queue, and a bounded array can prevent resource exhaustion. When the number of threads in the thread pool reaches corePoolSize, a new task comes in, and the task is placed at the end of the queue, waiting to be scheduled. If the queue is already full, a new thread is created, and if the number of threads has reached maxPoolSize, the reject policy is executed.

② LinkedBlockingQuene

Unbounded blocking queues based on linked lists (actually the maximum capacity is Interger.MAX), sorted by FIFO. Because of the nearly unbounded nature of the queue, when the number of threads in the thread pool reaches corePoolSize, new tasks will be stored in the queue all the time, instead of creating new threads until maxPoolSize, so the parameter maxPoolSize does not work when using the work queue.

③ SynchronousQuene

A blocking queue that does not cache a task, and the producer puts a task until the consumer takes it out. In other words, when a new task comes in, it is not cached, but is directly scheduled to execute the task. If no thread is available, a new thread is created, and if the number of threads reaches maxPoolSize, the reject policy is executed.

④ PriorityBlockingQueue

An unbounded blocking queue with priority, which is realized by the parameter Comparator.

VI. ThreadFactory Thread Factory

The factory used to create a new thread, which can be used to set the thread name, whether it is a daemon thread, and so on

7. Handler refusal strategy

When the tasks in the work queue have reached the maximum limit and the number of threads in the thread pool has reached the maximum limit, what if a new task is submitted? The rejection strategy here is to solve this problem. Four rejection strategies are provided in jdk:

① CallerRunsPolicy

Under this strategy, the run method of the rejected task is executed directly in the caller thread, and the task is abandoned unless the thread pool is already shutdown.

② AbortPolicy

Under this strategy, the task is discarded directly and a RejectedExecutionException exception is thrown.

③ DiscardPolicy

Under this strategy, simply discard the task and do nothing.

④ DiscardOldestPolicy

Under this strategy, discard the earliest task in the queue, and then try to put the rejected task in the queue.

Thank you for reading! This is the end of the article on "what is the meaning of Java thread pool parameters". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.