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Create a way

  • Executors.newWorkStealingPool();

    • Create a thread pool with preemptive operations

  • Executors.newScheduledThreadPool(10)

    • Create a fixed – length thread pool to support scheduled and periodic task execution.

  • Executors.newFixedThreadPool(10)

    • Create a fixed-length thread pool that controls the maximum number of concurrent threads, and the excess threads wait in the queue.

  • Executors.newSingleThreadExecutor()

    • Thread tasks are executed sequentially, but unlike a single thread, this thread pool only exists for one thread, and when that thread dies, another thread takes over and continues to execute tasks sequentially.

  • Executors.newCachedThreadPool()

    • Create a cacheable thread pool. If the length of the thread pool exceeds the processing requirement, you can recycle idle threads flexibly, or create a new thread if none is available. The thread pool is infinite

Seven parameters

  • Int corePoolSize: number of core threads
  • Int maximumPoolSize: specifies the maximum number of threads
  • Long keepAliveTime: indicates the idle time
  • TimeUnit unit: TimeUnit
  • BlockingQueue workQueue: Block queue
  • ThreadFactory ThreadFactory: ThreadFactory class
  • RejectedExecutionHandler Handler: Reject the policy

Thread pool processing flow

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Rejection policies

The JDK’s built-in rejection policy:

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A thread must be created using a thread pool

Do not allow the thread pool to be created by Executors because the maximum number of threads is set to Intege.MAX_VALUE = 21E+. If the thread is created wirelessly, it may cause OOM

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Create a thread pool using ThreadPoolExecutor:

# ThreadPoolExecutor
ExecutorService threadPool = new ThreadPoolExecutor(0, 10,
                60L, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>());
# Executors
ExecutorService threadPool = Executors.newCachedThreadPool();
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Handwritten thread pool

Public static void main(String[] args) {ExecutorService threadPool = new ThreadPoolExecutor(2,// ThreadPoolExecutor 5, New LinkedBlockingDeque<Runnable>(3), // Set the queue size, . The default is an Integer. MAX_VALUE Executors defaultThreadFactory (), / / thread factory new ThreadPoolExecutor CallerRunsPolicy ()); Try {for (int I = 0; i < 10; i++) { threadPool.execute(()->{ System.out.println(Thread.currentThread().getName()); }); } } catch (Exception e){ e.printStackTrace(); } finally { threadPool.shutdown(); }}Copy the code

How to set the maximum number of threads

1. CPU intensive

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Number of CPU cores + 1

Runtime.getRuntime().availableProcessors()+1
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2. IO intensive

  • First: since the IO intensive task thread is not a single task executing, configure as many threads as possible, such as CPU cores x 2
Runtime.getRuntime().availableProcessors() * 2
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  • The second:

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