public void execute(Runnable command) {
//如果提交的任务为空，则抛出空指针异常
if (command == null)
throw new NullPointerException();
//获取线程池的状态和线程池中线程的数量
int c = ctl.get();
//线程池中的线程数量小于corePoolSize的值
if (workerCountOf(c) < corePoolSize) {
//重新开启线程执行任务
if (addWorker(command, true))
return;
c = ctl.get();
}
//如果线程池处于RUNNING状态，则将任务添加到阻塞队列中
if (isRunning(c) && workQueue.offer(command)) {
//再次获取线程池的状态和线程池中线程的数量，用于二次检查
int recheck = ctl.get();
//如果线程池没有未处于RUNNING状态，从队列中删除任务
if (! isRunning(recheck) && remove(command))
//执行拒绝策略
reject(command);
//如果线程池为空，则向线程池中添加一个线程
else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}
//任务队列已满，则新增worker线程，如果新增线程失败，则执行拒绝策略
else if (!addWorker(command, false))
reject(command);
}

//线程池中的线程数量小于corePoolSize的值
if (workerCountOf(c) < corePoolSize) {
//重新开启线程执行任务
if (addWorker(command, true))
return;
c = ctl.get();
}

if (isRunning(c) && workQueue.offer(command)) 

//再次获取线程池的状态和线程池中线程的数量，用于二次检查
int recheck = ctl.get();
//如果线程池没有未处于RUNNING状态，从队列中删除任务
if (! isRunning(recheck) && remove(command))
//执行拒绝策略
reject(command);
//如果线程池为空，则向线程池中添加一个线程
else if (workerCountOf(recheck) == 0)
addWorker(null, false);

//任务队列已满，则新增worker线程，如果新增线程失败，则执行拒绝策略
else if (!addWorker(command, false))
reject(command);

private boolean addWorker(Runnable firstTask, boolean core) {
//标记重试的标识
retry:
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
// 检查队列是否在某些特定的条件下为空
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
 firstTask == null &&
 ! workQueue.isEmpty()))
return false;
//下面循环的主要作用为通过CAS方式增加线程的个数
for (;;) {
//获取线程池中的线程数量
int wc = workerCountOf(c);
//如果线程池中的线程数量超出限制，直接返回false
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
//通过CAS方式向线程池新增线程数量
if (compareAndIncrementWorkerCount(c))
//通过CAS方式保证只有一个线程执行成功，跳出最外层循环
break retry;
//重新获取ctl的值
c = ctl.get(); 
//如果CAS操作失败了，则需要在内循环中重新尝试通过CAS新增线程数量
if (runStateOf(c) != rs)
continue retry;
}
}

//跳出最外层for循环，说明通过CAS新增线程数量成功
//此时创建新的工作线程
boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try {
//将执行的任务封装成worker
w = new Worker(firstTask);
final Thread t = w.thread;
if (t != null) {
//独占锁，保证操作workers时的同步
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
//此处需要重新检查线程池状态
//原因是在获得锁之前可能其他的线程改变了线程池的状态
int rs = runStateOf(ctl.get());

if (rs < SHUTDOWN ||
(rs == SHUTDOWN && firstTask == null)) {
if (t.isAlive())
throw new IllegalThreadStateException();
//向worker中添加新任务
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
//将是否添加了新任务的标识设置为true
workerAdded = true;
}
} finally {
//释放独占锁
mainLock.unlock();
}
//添加新任成功，则启动线程执行任务
if (workerAdded) {
t.start();
//将任务是否已经启动的标识设置为true
workerStarted = true;
}
}
} finally {
//如果任务未启动或启动失败，则调用addWorkerFailed(Worker)方法
if (! workerStarted)
addWorkerFailed(w);
}
//返回是否启动任务的标识
return workerStarted;
}

// 检查队列是否在某些特定的条件下为空
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
 firstTask == null &&
 ! workQueue.isEmpty()))
return false;

for (;;) {
//获取线程池中的线程数量
int wc = workerCountOf(c);
//如果线程池中的线程数量超出限制，直接返回false
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
//通过CAS方式向线程池新增线程数量
if (compareAndIncrementWorkerCount(c))
//通过CAS方式保证只有一个线程执行成功，跳出最外层循环
break retry;
//重新获取ctl的值
c = ctl.get(); 
//如果CAS操作失败了，则需要在内循环中重新尝试通过CAS新增线程数量
if (runStateOf(c) != rs)
continue retry;
}

//跳出最外层for循环，说明通过CAS新增线程数量成功
//此时创建新的工作线程
boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try {
//将执行的任务封装成worker
w = new Worker(firstTask);
final Thread t = w.thread;
if (t != null) {
//独占锁，保证操作workers时的同步
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
//此处需要重新检查线程池状态
//原因是在获得锁之前可能其他的线程改变了线程池的状态
int rs = runStateOf(ctl.get());

if (rs < SHUTDOWN ||
(rs == SHUTDOWN && firstTask == null)) {
if (t.isAlive())
throw new IllegalThreadStateException();
//向worker中添加新任务
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
//将是否添加了新任务的标识设置为true
workerAdded = true;
}
} finally {
//释放独占锁
mainLock.unlock();
}
//添加新任成功，则启动线程执行任务
if (workerAdded) {
t.start();
//将任务是否已经启动的标识设置为true
workerStarted = true;
}
}
} finally {
//如果任务未启动或启动失败，则调用addWorkerFailed(Worker)方法
if (! workerStarted)
addWorkerFailed(w);
}
//返回是否启动任务的标识
return workerStarted;

private void addWorkerFailed(Worker w) {
//获取独占锁
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
//如果Worker任务不为空
if (w != null)
//将任务从workers集合中移除
workers.remove(w);
//通过CAS将任务数量减1
decrementWorkerCount();
tryTerminate();
} finally {
//释放锁
mainLock.unlock();
}
}

final void reject(Runnable command) {
handler.rejectedExecution(command, this);
}

private volatile RejectedExecutionHandler handler;

package java.util.concurrent;
public interface RejectedExecutionHandler {
 void rejectedExecution(Runnable r, ThreadPoolExecutor executor);
}

public class CustomPolicy implements RejectedExecutionHandler {
public CustomPolicy() { }
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
if (!e.isShutdown()) {
System.out.println("使用调用者所在的线程来执行任务")
r.run();
}
}
}

new ThreadPoolExecutor(0, Integer.MAX_VALUE,
 60L, TimeUnit.SECONDS,
 new SynchronousQueue<Runnable>(),
 Executors.defaultThreadFactory(),
 new CustomPolicy());