consumer.suspend();
consumer.updateCorePoolSize(3);
try {
	TimeUnit.SECONDS.sleep(65000L);
 } catch (Exception e) {
	log.error("InterruptException", e);
}
consumer.resume();

import lombok.SneakyThrows;
import lombok.extern.slf4j.Slf4j;
import org.apache.rocketmq.common.ThreadFactoryImpl;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
@Slf4j
public class ThreadTest {
   public static void main(String[] args) throws InterruptedException {
       ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
               10,
               50,
               1000 * 60,
               TimeUnit.MILLISECONDS,
               new LinkedBlockingQueue<>(),
               new ThreadFactoryImpl("test" + "_" + "ConsumeMessageThread_"));
       for (int i = 0; i < 1000; i++) {
           threadPoolExecutor.submit(new Runnable() {
               @SneakyThrows
               @Override
               public void run() {
                   Thread.sleep(5);
                   log.info("hello");
               }
           });
       }
       log.info("coreSize: {}" ,threadPoolExecutor.getCorePoolSize());
       Thread.sleep(10000L);
       threadPoolExecutor.setCorePoolSize(3);
       log.info("coreSize: {}" ,threadPoolExecutor.getCorePoolSize());
       // Thread.sleep(1000*60); // 如果休眠時(shí)間大于KeepAliveTime將會(huì)只有3個(gè)線程
       Thread.sleep(1000L);  // 休眠時(shí)間不夠時(shí)仍然有10個(gè)線程
       for (int i = 0; i < 1000; i++) {
           threadPoolExecutor.submit(new Runnable() {
               @SneakyThrows
               @Override
               public void run() {
                   Thread.sleep(10);
                   log.info("hello2");
               }
           });
       }
   }
}

    // 工作workers, work只有在獲取任務(wù)超時(shí)以后才會(huì)從workers中刪除
    private final HashSet<Worker> workers = new HashSet<Worker>();
    public void setCorePoolSize(int corePoolSize) {
        if (corePoolSize < 0)
            throw new IllegalArgumentException();
        int delta = corePoolSize - this.corePoolSize;
        this.corePoolSize = corePoolSize;
        if (workerCountOf(ctl.get()) > corePoolSize)
        // 減少核心線程數(shù)以后進(jìn)入interruptIdleWorkers方法
            interruptIdleWorkers();
        else if (delta > 0) {
            int k = Math.min(delta, workQueue.size());
            while (k-- > 0 && addWorker(null, true)) {
                if (workQueue.isEmpty())
                    break;
            }
        }
    }
     private void interruptIdleWorkers(boolean onlyOne) {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (Worker w : workers) {
                Thread t = w.thread;
                if (!t.isInterrupted() && w.tryLock()) {
                    try {
                        // 在interruptIdleWorkers方法中只是將work的線程中斷，并沒有從workers刪除
                        t.interrupt();
                    } catch (SecurityException ignore) {
                    } finally {
                        w.unlock();
                    }
                }
                if (onlyOne)
                    break;
            }
        } finally {
            mainLock.unlock();
        }
    }
   final void runWorker(Worker w) {
        Thread wt = Thread.currentThread();
        Runnable task = w.firstTask;
        w.firstTask = null;
        w.unlock(); // allow interrupts
        boolean completedAbruptly = true;
        try {
           // 重點(diǎn)是getTask()方法獲取task失敗才會(huì)中斷循環(huán)
            while (task != null || (task = getTask()) != null) {
                w.lock();
                if ((runStateAtLeast(ctl.get(), STOP) ||
                     (Thread.interrupted() &&
                      runStateAtLeast(ctl.get(), STOP))) &&
                    !wt.isInterrupted())
                    wt.interrupt();
                try {
                    beforeExecute(wt, task);
                    Throwable thrown = null;
                    try {
                        task.run();
                    } catch (RuntimeException x) {
                        thrown = x; throw x;
                    } catch (Error x) {
                        thrown = x; throw x;
                    } catch (Throwable x) {
                        thrown = x; throw new Error(x);
                    } finally {
                        afterExecute(task, thrown);
                    }
                } finally {
                    task = null;
                    w.completedTasks++;
                    w.unlock();
                }
            }
            completedAbruptly = false;
        } finally {
            processWorkerExit(w, completedAbruptly);
        }
    }
   private Runnable getTask() {
        boolean timedOut = false; // Did the last poll() time out?
        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);
            // Check if queue empty only if necessary.
            if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
                decrementWorkerCount();
                return null;
            }
            int wc = workerCountOf(c);
            // Are workers subject to culling?
            boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
            // 超時(shí)以后進(jìn)入這里的if返回null然后work才會(huì)被銷毀
            if ((wc > maximumPoolSize || (timed && timedOut))
                && (wc > 1 || workQueue.isEmpty())) {
                if (compareAndDecrementWorkerCount(c))
                    return null;
                continue;
            }
            try {
                Runnable r = timed ?
                    workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                    workQueue.take();
                if (r != null)
                    return r;
                timedOut = true;
            } catch (InterruptedException retry) {
                timedOut = false;
            }
        }
    }
   private void processWorkerExit(Worker w, boolean completedAbruptly) {
        if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted
            decrementWorkerCount();
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            completedTaskCount += w.completedTasks;
            // 這里才真正將worker刪除
            workers.remove(w);
        } finally {
            mainLock.unlock();
        }
        tryTerminate();
        int c = ctl.get();
        if (runStateLessThan(c, STOP)) {
            if (!completedAbruptly) {
                int min = allowCoreThreadTimeOut ? 0 : corePoolSize;
                if (min == 0 && ! workQueue.isEmpty())
                    min = 1;
                if (workerCountOf(c) >= min)
                    return; // replacement not needed
            }
            addWorker(null, false);
        }
    }