线程池最大线程数不正确

Question

我有一个最大线程数为3的线程池，但是只执行了一个线程，怎么回事？

public class Volatile {

    private volatile static boolean keepA = true;
    private static boolean keepB = true;

    private static ExecutorService executor = new ThreadPoolExecutor(1,
            3, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<>() );

    public static void main(String[] args) {
        executor.execute(() -> {
            while (keepA) {
                System.out.println("keepA running...");
            }
            System.out.println("keepA stop!!!!!!");
        });
        executor.execute(() -> {
            while (keepB) {
                System.out.println("keepB running...");
            }
            System.out.println("keepB stop!!!!!!");
        });
        executor.execute(() -> {
            keepA = false;
            keepB = false;
        });
        while (true) {

        }
    }
}

结果

keepA running...
keepA running...
keepA running...
......

Answer 1

ThreadPoolExecutor 的第一个参数是并行线程的初始数量运行。您已将其设置为 1。将其更改为 3，然后重试。只有当队列已满时，此大小才应该增长，但您的队列是无限大的，永远不会满。

public ThreadPoolExecutor(int corePoolSize,
              int maximumPoolSize,
              long keepAliveTime,
              TimeUnit unit,
              BlockingQueue<Runnable> workQueue)
Creates a new ThreadPoolExecutor with the given initial parameters and default rejected execution handler.

Parameters:

corePoolSize - the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set

maximumPoolSize - the maximum number of threads to allow in the pool

keepAliveTime - when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.

unit - the time unit for the keepAliveTime argument

workQueue - the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method.

Throws:
IllegalArgumentException - if one of the following holds:
`corePoolSize < 0`
`keepAliveTime < 0`
`maximumPoolSize <= 0`
`maximumPoolSize < corePoolSize` 
NullPointerException - if workQueue or threadFactory is null

Answer 2

非核心线程只会在队列已满时启动（并且您有一个无界队列，因此永远不会发生）。

作为per Javadoc:

Any BlockingQueue may be used to transfer and hold submitted tasks. The use of this queue interacts with pool sizing:

If fewer than corePoolSize threads are running, the Executor always prefers adding a new thread rather than queuing.

If corePoolSize or more threads are running, the Executor always prefers queuing a request rather than adding a new thread.

If a request cannot be queued, a new thread is created unless this would exceed maximumPoolSize, in which case, the task will be rejected.

线程池最大线程数不正确

The maximum number of threads in the thread pool is incorrect

java

threadpool

executorservice

threadpoolexecutor