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This article introduces the relevant knowledge of "what is the knowledge of ThreadPoolExecutor in java". In the operation of actual cases, many people will encounter such a dilemma. Next, let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Thread pool technology is often used in concurrency, and the use of thread pool in java is realized by calling ThreadPoolExecutor. ThreadPoolExecutor provides four constructors, all of which boil down to the following:

/ / Constructor public ThreadPoolExecutor (int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,BlockingQueue workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler) with seven parameters

The meaning of these parameters is as follows:

CorePoolSize: maximum number of core threads in this thread pool maximumPoolSize: maximum total number of threads in this thread pool keepAliveTime: unit workQueue of idle timeout unit:keepAliveTime of non-core threads in this thread pool: blocking queue BlockingQueue, maintaining the Runnable object waiting for execution threadFactory: the interface to create the thread, need to implement its Thread newThread (Runnable r) method. RejectedExecutionHandler: saturation policy, the execute method will call RejectedExecutionHandler when the maximum thread and work queue capacity is saturated.

ThreadPoolExecutor workflow

The flow chart is as follows:

The general process statement is as follows:

Add tasks to the thread pool, and when the number of tasks is less than corePoolSize, an thead is automatically created to handle these tasks; when the number of added tasks is greater than corePoolSize and less than maximmPoolSize, threads are not created, but these tasks are placed in the blocking queue, waiting to be executed; following the conditions of the above 2, and when the blocking queue is full, continue to create thread, thus speeding up the processing of blocking queues When the added task is greater than maximmPoolSize, it is decided whether to continue adding tasks to the thread pool according to the saturation policy. The default saturation policy is AbortPolicy (direct discarding).

Blocking queues used in the thread pool

ArrayBlockingQueue: bounded blocking queue based on array structure. Constructor must pass size, FIFO (first-in, first-out); LinkedBlockingQueue: unbounded, default size 65536 (Integer.MAX_VALUE). When a large number of tasks are requested, it is easy to run out of memory. SynchronousQueue: the synchronization queue is a special BlockingQueue that has no capacity (because in SynchronousQueue, the insert will wait for another thread to delete, and vice versa). DelayedWorkQueue: when this queue receives a task, it first joins the queue. Only when the specified delay time is reached will the task be executed.

Common methods for blocking queues are shown in the following table:

Add adds an element if the queue is full, it throws an IIIegaISlabEepeplian exception remove removes and returns the queue header element if the queue is empty, throws a NoSuchElementException exception element returns the queue header element if the queue is empty, throws a NoSuchElementException exception offer adds an element and returns true if the queue is full, returns false poll to remove and question the queue header element if the queue is empty Return null peek returns the element of the queue header if the queue is empty, return null put to add an element if the queue is full, block take remove and return the element of the queue header if the queue is empty, block

Four common thread pools

NewCachedThreadPool newFixedThreadPool newSingleThreadExecutor newScheduledThreadPool

CachedThreadPool SynchronousQueue (queue length can be increased infinitely, maximum Integer.MAX_VALUE default 60 second timeout FixedThreadPool LinkedBlockingQueue (queue length unlimited) can specify nThreads, fixed number of no timeout newSingleThreadExecutor LinkedBlockingQueue (queue length infinite), fixed 1 no timeout newScheduledThreadPool DelayedWorkQueue can increase, maximum value Integer.MAX_VALUE does not timeout

They are called directly as static methods through Executors, essentially they end up calling the constructor of ThreadPoolExecutor, the first piece of code in this article.

Note: if KeepAliveTime=0, it means not waiting

"Alibaba java Development Manual" suggests that thread pools are not created by Executors, but by ThreadPoolExecutor, which makes writers more clear about the running rules of thread pools and avoid the risk of resource exhaustion.

The above is the whole content of this article. I hope it will be helpful to your study, and I hope you will support us more.

Title of this article: summary of ThreadPoolExecutor common sense in java

Note the description of the method name

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