重要属性
//ctl是一个原子整数，包含两个概念字段workerCount，指示线程的有效运行状态数，指示是否正在运行、正在关闭等,前29位标识线程数量，后3位标识状态
//workerCount是允许启动和不允许停止的工人数。该值可能与实际线程的实际数量不同，例如当线程工厂在被请求时无法创建线程时，以及退出线程在终止之前仍在执行簿记。用户可见池大小报告为工作集的当前大小。
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
//主要是对worker集合进行锁定,保证退出时的中断
private final ReentrantLock mainLock = new ReentrantLock();
//存放工作线程的地方
private final HashSet<Worker> workers = new HashSet<Worker>();
线程池的运行状态
RUNNING
接受新任务并处理排队的任务
SHUTDOWN
不接受新任务，但处理排队的任务
STOP
不接受新任务，不处理排队的任务,并且中断正在进行的任务
TIDYING
所有任务都已终止，workerCount为零，转换为状态整理的线程，将运行terminated（）钩子方法
TERMINATED
TERMINATED（）已完成
这些值之间的数字顺序很重要，以便进行有序比较。运行状态随时间单调地增加，但不必命中每个状态。过程是：
1.RUNNING -> SHUTDOWN 调用shutdown（）时，可能隐式地在finalize（）中
2.(RUNNING or SHUTDOWN) -> STOP 调用shutdownNow的时候
3.SHUTDOWN -> TIDYING 队列和线程池为空的时候
4.STOP -> TIDYING 当线程池为空的时候
5.TIDYING -> TERMINATED 当terminated（）钩子方法完成时
等待awaitTermination（）的线程将在状态达到TERMINATED时返回。
构造函数
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), defaultHandler);
}
execute方法
public void execute(Runnable command) {
if (command == null)
throw new NullPointerException();
int c = ctl.get();
//workerCountOf获取线程数量，判断是否小于核心线程数
if (workerCountOf(c) < corePoolSize) {
//创建核心线程
if (addWorker(command, true))
return;
c = ctl.get();
}
//核心线程满了就塞到阻塞队列里
if (isRunning(c) && workQueue.offer(command)) {
//再检查一遍如果不是运行状态就拒绝
int recheck = ctl.get();
if (! isRunning(recheck) && remove(command))
reject(command);
//如果工作线程是0，新增非核心线程池
else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}
//阻塞队列也塞不下了执行拒绝策略,就创建非核心线程，如果非核心线程创建失败就执行拒绝策略
else if (!addWorker(command, false))
reject(command);
}
//新建线程并添加到核心线程池中
//1.先增加数量2.添加到set 3.再运行方法
private boolean addWorker(Runnable firstTask, boolean core) {
retry:
for (;;) {
//rs线程的运行状态
int c = ctl.get();
int rs = runStateOf(c);
// Check if queue empty only if necessary.
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty()))
return false;
for (;;) {
int wc = workerCountOf(c);
//数量校验，如果没有通过返回false
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
//CAS增加workCount
if (compareAndIncrementWorkerCount(c))
break retry;
c = ctl.get(); // Re-read ctl
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 {
//新建work
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());
//这里判断一下线程池的运行状态
if (rs < SHUTDOWN ||
(rs == SHUTDOWN && firstTask == null)) {
if (t.isAlive()) // precheck that t is startable
throw new IllegalThreadStateException();
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
//worker添加成功开始运行
if (workerAdded) {
t.start();
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
}
Worker#run方法
final void runWorker(Worker w) {
//获取当前线程
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
//将任务置空
w.firstTask = null;
w.unlock(); // allow interrupts
boolean completedAbruptly = true;
try {
while (task != null || (task = getTask()) != null) {
//锁住自己 调用AQS的acquire(1)
w.lock();
//如果线程池的状态是STOPPING,确保线程已经被中断，如果没有中断，确保线程没有中断
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 {
//把worker从线程池踢出
processWorkerExit(w, completedAbruptly);
}
}
woker##getTask 工作线程拉取任务
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())) {
//woker-1
decrementWorkerCount();
return null;
}
int wc = workerCountOf(c);
// Are workers subject to culling?
boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
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;
}
}
}
