CSDN地址：https://blog.csdn.net/Eclipse_2019/article/details/127382473
我们先看下初始化5个参数
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), defaultHandler);
}
public ThreadPoolExecutor(int corePoolSize, //主线程数
int maximumPoolSize, //最大线程数
long keepAliveTime, //线程存活时间 （除主线程外，其他的线程在没有任务执行的时候需要回收，多久后回收）
TimeUnit unit, //存活时间的时间单位
BlockingQueue workQueue, //阻塞队列，我们需要执行的task都在该队列
ThreadFactory threadFactory, //生成thread的工厂
RejectedExecutionHandler handler) { //拒绝饱和策略，当队列满了并且线程个数达到 maximunPoolSize 后采取的策略
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.acc = System.getSecurityManager() == null ?
null :
AccessController.getContext();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
} 
public void execute(Runnable command) {
if (command == null) //如果要执行的任务是空的，异常
throw new NullPointerException();
/*
* Proceed in 3 steps:
*
* 1. If fewer than corePoolSize threads are running, try to
* start a new thread with the given command as its first
* task. The call to addWorker atomically checks runState and
* workerCount, and so prevents false alarms that would add
* threads when it shouldn't, by returning false.
*
* 2. If a task can be successfully queued, then we still need
* to double-check whether we should have added a thread
* (because existing ones died since last checking) or that
* the pool shut down since entry into this method. So we
* recheck state and if necessary roll back the enqueuing if
* stopped, or start a new thread if there are none.
*
* 3. If we cannot queue task, then we try to add a new
* thread. If it fails, we know we are shut down or saturated
* and so reject the task.
*/
int c = ctl.get();//111000...000
//高三位代表线程池的状态，低29位代表线程池中的线程数量
//如果线程数小于主线程数，添加线程
if (workerCountOf(c) < corePoolSize) {
if (addWorker(command, true))
return;
c = ctl.get();
}
//如果超过主线程数，将任务添加至workqueue 阻塞队列
if (isRunning(c) && workQueue.offer(command)) {
int recheck = ctl.get();
//再判断一次运行状态，如果线程池不处于running状态，则把刚加进队列的任务移除，如果移除成功则往下走进行拒绝
if (! isRunning(recheck) && remove(command))
reject(command);
//接着上一个条件，如果移除失败则判断是否有工作线程，如果当前线程池线程空，则添加一个线程
else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}
//如果超过主线程数且添加阻塞队列失败，则增加非核心线程，如果添加非核心线程也失败，则拒绝
else if (!addWorker(command, false))
reject(command);
}private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));//111000...000
private static final int COUNT_BITS = Integer.SIZE - 3;//29
private static final int CAPACITY = (1 << COUNT_BITS) - 1;//00011111 11111111 11111111 11111111
//00000000 00000000 00000000 00000001 << 29 =
//00100000 00000000 00000000 00000000 -1 =
//00011111 11111111 11111111 11111111
// runState is stored in the high-order bits
private static final int RUNNING = -1 << COUNT_BITS; //11100000 ... 000
//-1 原码: 10000000 00000000 00000000 00000001
//-1 反码: 11111111 11111111 11111111 11111110
//-1 补码: 11111111 11111111 11111111 11111111 <<29=
// 11100000 0000000 00000000 00000000
private static final int SHUTDOWN = 0 << COUNT_BITS;//00000000 ... 000
private static final int STOP = 1 << COUNT_BITS;//001 0000 ... 000
private static final int TIDYING = 2 << COUNT_BITS;//010 0000 ... 000
private static final int TERMINATED = 3 << COUNT_BITS;//011 0000 ... 000
1、RUNNING
(1) 状态说明：线程池处在RUNNING状态时，能够接收新任务，以及对已添加的任务进行处理。
(02) 状态切换：线程池的初始化状态是RUNNING。换句话说，线程池被一旦被创建，就处于RUNNING状态，并且线程池中的任务数为0！
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
2、 SHUTDOWN
(1) 状态说明：线程池处在SHUTDOWN状态时，不接收新任务，但能处理已添加的任务。
(2) 状态切换：调用线程池的shutdown()接口时，线程池由RUNNING -> SHUTDOWN。
3、STOP
(1) 状态说明：线程池处在STOP状态时，不接收新任务，不处理已添加的任务，并且会中断正在处理的任务。
(2) 状态切换：调用线程池的shutdownNow()接口时，线程池由(RUNNING or SHUTDOWN ) -> STOP。
4、TIDYING
(1) 状态说明：当所有的任务已终止，ctl记录的”任务数量”为0，线程池会变为TIDYING状态。当线程池变为TIDYING状态时，会执行钩子函数terminated()。terminated()在ThreadPoolExecutor类中是空的，若用户想在线程池变为TIDYING时，进行相应的处理；可以通过重载terminated()函数来实现。
(2) 状态切换：当线程池在SHUTDOWN状态下，阻塞队列为空并且线程池中执行的任务也为空时，就会由 SHUTDOWN -> TIDYING。
当线程池在STOP状态下，线程池中执行的任务为空时，就会由STOP -> TIDYING。
5、 TERMINATED
(1) 状态说明：线程池彻底终止，就变成TERMINATED状态。
(2) 状态切换：线程池处在TIDYING状态时，执行完terminated()之后，就会由 TIDYING -> TERMINATED。
private static int runStateOf(int c) { return c & ~CAPACITY; }
private static int workerCountOf(int c) { return c & CAPACITY; }//CAPACITY:000111...111
private static int ctlOf(int rs, int wc) { return rs | wc; }private boolean addWorker(Runnable firstTask, boolean core) {
retry: //goto语句 叫demo
//自旋检查线程池的状态。阻塞队列是否为空等判断
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
// Check if queue empty only if necessary.
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty()))//如果线程池的运行状态是running的话直接跳过该条件语句往下走，如果是>=SHUTDOWN的话就往后判断（为什么不直接返回false不让他创建worker呢，因为在shutdown状态是可以创建线程去处理阻塞队列里的任务的）
//此时因为rs>=SHTDOWN了，所以会先判断是否等于SHUTDOWN，如果不等于就直接返回false不让创建worker，如果等于的话接着往下判断
//如果当前任务不为空直接返回false不让创建worker，（这里为什么当前任务为空就直接不让创建worker呢，就是因为shutdown状态不能再接收新任务。
//如果当前任务为空则判断阻塞队列是否为空，如果为空则返回false，不让创建worker，如果不为空就不走这个条件，接着往下走
return false;
//自旋
for (;;) {
int wc = workerCountOf(c);
//如果现有线程数大于最大值，或者大于等于最大线程数（主线程数）
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
//cas添加线程
if (compareAndIncrementWorkerCount(c))
break retry;
c = ctl.get(); // Re-read ctl
//如果失败了，继续外层循环判断
if (runStateOf(c) != rs)
continue retry;
// else CAS failed due to workerCount change; retry inner loop
}
}
boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try {
//开启一个线程，Worker实现了runnable接口
w = new Worker(firstTask);
final Thread t = w.thread;
if (t != null) {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
// Recheck while holding lock.
// Back out on ThreadFactory failure or if
// shut down before lock acquired.
int rs = runStateOf(ctl.get());
if (rs < SHUTDOWN ||
(rs == SHUTDOWN && firstTask == null)) {
if (t.isAlive()) // precheck that t is startable
throw new IllegalThreadStateException();
//添加至wokers
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
//添加成功
if (workerAdded) {
t.start(); //启动线程，会调用我们线程的run接口，也就是我们worker的run
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
} retry:
for (int i = 0; i < 3; i++) {
for (int j = 3; j < 10; j++) {
// if (j == 4) {
// break retry; //跳出外面循环
// }
if (j == 7) {
continue retry; //继续外面循环
}
System.out.println(i+":"+j);
}
}Worker(Runnable firstTask) {
setState(-1); // inhibit interrupts until runWorker 禁止中断，直到runWorker
this.firstTask = firstTask;
this.thread = getThreadFactory().newThread(this);
}final void runWorker(Worker w) {
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock(); // allow interrupts
boolean completedAbruptly = true;
try { //只要一直能获取到task，就一直会执行，不会关闭，所以线程也不会销毁，线程销毁只有当task为null
while (task != null || (task = getTask()) != null) {
w.lock();
// If pool is stopping, ensure thread is interrupted;
// if not, ensure thread is not interrupted. This
// requires a recheck in second case to deal with
// shutdownNow race while clearing interrupt
if ((runStateAtLeast(ctl.get(), STOP) ||
(Thread.interrupted() &&
runStateAtLeast(ctl.get(), STOP))) &&
!wt.isInterrupted())
wt.interrupt();
try {
//调用线程方法之前执行
beforeExecute(wt, task);
Throwable thrown = null;
try {
//调用task的run方法
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 {
//调用线程方法之后执行
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? //自旋获取
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
// Check if queue empty only if necessary. 必要时检查空，状态是否停止或者shutdown
if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
decrementWorkerCount();
return null;
}
//获取线程数量
int wc = workerCountOf(c);
// Are workers subject to culling?
//线程数大于主线程数时，或者allowCoreThreadTimeOut参数为true allowCoreThreadTimeOut默认为false
boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
//超过最大线程，或者timed为true ,&& wc大于1个，并且任务队列为空的时候
if ((wc > maximumPoolSize || (timed && timedOut))
&& (wc > 1 || workQueue.isEmpty())) {
//线程数-1，并且返回null，该线程结束
if (compareAndDecrementWorkerCount(c))
return null;
continue;
}
try {
//如果time是true，超过时间不阻塞，不然一直阻塞，不回收
Runnable r = timed ?
workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
//移除并返回队列头部的元素，如果为空，超过时间返回null
workQueue.take();
//移除并返回队列头部的元素，如果为空,一直阻塞
if (r != null)
return r;
timedOut = true;
} catch (InterruptedException retry) {
timedOut = false;
}
}
}页面更新：2024-06-10
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