java - ExecutorService 中的活动线程

Question

任何想法如何确定当前运行的活动线程数ExecutorService？

Answer 1

使用ThreadPoolExecutor实现并调用getActiveCount()：

int getActiveCount() 
// Returns the approximate number of threads that are actively executing tasks.

ExecutorService 接口没有为此提供方法，它取决于实现。

Answer 2

假设pool是 ExecutorService 实例的名称：

if (pool instanceof ThreadPoolExecutor) {
    System.out.println(
        "Pool size is now " +
        ((ThreadPoolExecutor) pool).getActiveCount()
    );
}

Answer 3

检查源代码Executors.newFixedThreadPool()：

return new ThreadPoolExecutor(nThreads, nThreads,
                              0L, TimeUnit.MILLISECONDS,
                              new LinkedBlockingQueue<Runnable>());

ThreadPoolExecutor 有一个 getActiveCount() 方法。因此，您可以将 ExecutorService 转换为 ThreadPoolExecutor，或者直接使用上面的代码获取一个。然后您可以调用getActiveCount().

Answer 4

ExecutorService 接口没有定义检查池中工作线程数量的方法，因为这是一个实现细节

public int getPoolSize()
Returns the current number of threads in the pool.

在 ThreadPoolExecutor 类上可用

导入 java.util.concurrent.LinkedBlockingQueue；
导入 java.util.concurrent.ThreadPoolExecutor；
导入 java.util.concurrent.TimeUnit；


公共类池大小 {

    公共静态无效主要（字符串[]参数）{
        ThreadPoolExecutor 执行器 = new ThreadPoolExecutor(10, 20, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue());
        System.out.println(executor.getPoolSize());
    }
}

但这需要您显式创建 ThreadPoolExecutor，而不是使用返回 ExecutorService 对象的 Executors 工厂。您始终可以创建自己的工厂来返回 ThreadPoolExecutors，但您仍然会留下使用具体类型而不是其接口的糟糕形式。

一种可能性是提供您自己的 ThreadFactory，它在已知线程组中创建线程，然后您可以计算

导入 java.util.concurrent.ExecutorService；
导入 java.util.concurrent.Executors；
导入 java.util.concurrent.ThreadFactory；


公共类 PoolSize2 {

    公共静态无效主要（字符串[]参数）{
        final ThreadGroup threadGroup = new ThreadGroup("workers");

        ExecutorService executor = Executors.newCachedThreadPool(new ThreadFactory() {
            公共线程 newThread(Runnable r) {
                返回新线程（线程组，r）；
            }
        });

        System.out.println(threadGroup.activeCount());
    }
}

Answer 5

我有同样的问题，所以创建了一个简单的 Runnable 来跟踪 ExecutorService 实例。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadPoolExecutor;

public class ExecutorServiceAnalyzer implements Runnable
{
    private final ThreadPoolExecutor threadPoolExecutor;
    private final int timeDiff;

    public ExecutorServiceAnalyzer(ExecutorService executorService, int timeDiff)
    {
        this.timeDiff = timeDiff;
        if (executorService instanceof ThreadPoolExecutor)
        {
            threadPoolExecutor = (ThreadPoolExecutor) executorService;
        }
        else
        {
            threadPoolExecutor = null;
            System.out.println("This executor doesn't support ThreadPoolExecutor ");
        }

    }

    @Override
    public void run()
    {
        if (threadPoolExecutor != null)
        {
            do
            {
                System.out.println("#### Thread Report:: Active:" + threadPoolExecutor.getActiveCount() + " Pool: "
                        + threadPoolExecutor.getPoolSize() + " MaxPool: " + threadPoolExecutor.getMaximumPoolSize()
                        + " ####");
                try
                {
                    Thread.sleep(timeDiff);
                }
                catch (Exception e)
                {
                }
            } while (threadPoolExecutor.getActiveCount() > 1);
            System.out.println("##### Terminating as only 1 thread is active ######");
        }

    }
}

您可以简单地将它与您的执行程序一起使用来获取 ThreadPool 的状态

前任

ExecutorService executorService = Executors.newFixedThreadPool(4);
    executorService.execute(new ExecutorServiceAnalyzer(executorService, 1000));

Answer 6

在线程上放置一个静态 volatile 计数器，该计数器在线程被激活和停用时更新。另请参阅 API。