import java.util.LinkedList; import java.util.List; import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock;  public class DdqThreadPool {     private static final class DdqThread extends Thread {         private Runnable runnable;         private final ReentrantLock reentrantLock = new ReentrantLock();         private final Condition condition = reentrantLock.newCondition();          public void setRunnable(Runnable runnable) {             try {                 reentrantLock.lock();                 this.runnable = runnable;                 condition.signalAll();             } catch (Exception exception) {                 throw new RuntimeException(exception);             } finally {                 reentrantLock.unlock();             }         }          @Override         public void run() {             while (true) {                 try {                     reentrantLock.lock();                     while (runnable == null) condition.await();                     runnable.run();                     runnable = null;                 } catch (Exception exception) {                     throw new RuntimeException(exception);                 } finally {                     reentrantLock.unlock();                 }             }          }     }      private List threads;      private AtomicInteger threadSize;      private DdqThreadPool(List ddqThreads) {         this.threads = ddqThreads;         this.threadSize = new AtomicInteger(ddqThreads.size());     }      public static DdqThreadPool newDdqThreadPool(int maxThreadSize) {         if (maxThreadSize < 1) throw new IllegalArgumentException("线程数量必须大于0");         List ddqThreads = new LinkedList<>();         for (int idx = 0; idx < maxThreadSize; idx++) {             DdqThread ddqThread = new DdqThread();             ddqThread.start();             ddqThreads.add(ddqThread);         }         return new DdqThreadPool(ddqThreads);     }      public void execute(Runnable runnable) {         if (runnable == null) throw new IllegalArgumentException("runnable不能为null");         int oldThreadSize1 = threadSize.get();         if (oldThreadSize1 < 1) return;         if (!threadSize.compareAndSet(oldThreadSize1, oldThreadSize1 - 1)) return;         DdqThread idleThread = threads.remove(0);         idleThread.setRunnable(runnable);         //以下三段代码可能还存在bug，因为idleThread.setRunnable(runnable)后，由于是异步执行，可能会存在着线程没执行完，但是忙碌线程又被添加回了可用线程集合         int oldThreadSize2;         while (!threadSize.compareAndSet((oldThreadSize2 = threadSize.get()), oldThreadSize2 + 1)) ;         threads.add(idleThread);     } }  

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