状态常量及其标志位获取方法
public class ThreadPoolExecutor extends AbstractExecutorService {
// 线程池状态控制位
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
// 偏移量，高3位存线程池的状态，其他29位存线程数
private static final int COUNT_BITS = Integer.SIZE - 3;
private static final int CAPACITY = (1 << COUNT_BITS) - 1;
// 线程池运行状态 11100000000000000000000000000000
private static final int RUNNING = -1 << COUNT_BITS;
// 线程池关闭状态，拒绝新线程，等待池中、工作队列中线程完成 00000000000000000000000000000000 ；
private static final int SHUTDOWN = 0 << COUNT_BITS;
// 线程池停止状态，拒绝新线程，会中断池中、工作队列中线程 00100000000000000000000000000000；
private static final int STOP = 1 << COUNT_BITS;
// 整理状态，线程池与工作队列都已经空了 01000000000000000000000000000000
private static final int TIDYING = 2 << COUNT_BITS;
// 终止状态 01100000000000000000000000000000
private static final int TERMINATED = 3 << COUNT_BITS;
// 灵巧的从32进制位中取出需要的状态码
private static int runStateOf(int c) { return c & ~CAPACITY; }
private static int workerCountOf(int c) { return c & CAPACITY; }
private static int ctlOf(int rs, int wc) { return rs | wc; }
关键属性
// 工作队列
private final BlockingQueue<Runnable> workQueue;
// 独占重入锁，用于锁住并发操作
private final ReentrantLock mainLock = new ReentrantLock();
// 线程池
private final HashSet<Worker> workers = new HashSet<Worker>();
// 重入锁条件
private final Condition termination = mainLock.newCondition();
// 获取的最大池大小
private int largestPoolSize;
// 已经完成的任务
private long completedTaskCount;
// 线程工厂
private volatile ThreadFactory threadFactory;
// 拒绝策略
private volatile RejectedExecutionHandler handler;
// 线程活跃时间，超过则回收，allowCoreThreadTimeOut为false的时候，针对的是>corePoolSize的那一部分
private volatile long keepAliveTime;
// 是否可以回收核心线程，空闲时间，设置为true后，核心线程也会在>keepAliveTime时被回收
private volatile boolean allowCoreThreadTimeOut;
// 池核心线程数
private volatile int corePoolSize;
// 池最大线程数
private volatile int maximumPoolSize;
// 默认的拒绝策略，策略为拒绝新任务，且抛出异常
private static final RejectedExecutionHandler defaultHandler =
new AbortPolicy();
工作线程
继承了AQS接口，实现自定义的锁机制
private final class Worker
extends AbstractQueuedSynchronizer
implements Runnable
{
private static final long serialVersionUID = 6138294804551838833L;
// 运行任务的线程
final Thread thread;
// 执行的第一个任务
Runnable firstTask;
// 当前工作者，已经执行完成的任务
volatile long completedTasks;
Worker(Runnable firstTask) {
// 锁状态为-1，原因是，直到runWorker前不也中断，在runWorker，将state由-1->0
setState(-1); // inhibit interrupts until runWorker
this.firstTask = firstTask;
this.thread = getThreadFactory().newThread(this);
}
public void run() {
runWorker(this);
}
protected boolean isHeldExclusively() {
return getState() != 0;
}
protected boolean tryAcquire(int unused) {
if (compareAndSetState(0, 1)) {
setExclusiveOwnerThread(Thread.currentThread());
return true;
}
return false;
}
protected boolean tryRelease(int unused) {
setExclusiveOwnerThread(null);
setState(0);
return true;
}
public void lock() { acquire(1); }
public boolean tryLock() { return tryAcquire(1); }
public void unlock() { release(1); }
public boolean isLocked() { return isHeldExclusively(); }
void interruptIfStarted() {
Thread t;
if (getState() >= 0 && (t = thread) != null && !t.isInterrupted()) {
try {
t.interrupt();
} catch (SecurityException ignore) {
}
}
}
}
executor
public void execute(Runnable command) {
if (command == null)
throw new NullPointerException();
// 获取线程状态
int c = ctl.get();
// 判断线程数是否小于核心线程数
if (workerCountOf(c) < corePoolSize) {
// 创建工作线程，关联任务
if (addWorker(command, true))
return;
c = ctl.get();
}
// 大于核心数、线程池是否是在运行，RUNING状态，且加入工作队列
if (isRunning(c)
&& workQueue.offer(command)) {
// 入队成功后，需要重新检查，是否池还在RUNING，不在的话需要删除入队的任务
int recheck = ctl.get();
if (! isRunning(recheck) && remove(command))
// 并启用拒绝策略
reject(command);
// 如果线程池空了，则需要创建一个工作线程来执行任务。
else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}
// 如果入队失败，则代表工作队列满了，则启用拒绝策略
else if (!addWorker(command, false))
reject(command);
}
submit
submit与execute的区别主要是有任务的返回结果，ThreadPoolExecutor没有对其重写，用的是父类的AbstractExecutorService
public Future<?> submit(Runnable task) {
if (task == null) throw new NullPointerException();
RunnableFuture<Void> ftask = newTaskFor(task, null);
execute(ftask);
return ftask;
}
public <T> Future<T> submit(Runnable task, T result) {
if (task == null) throw new NullPointerException();
RunnableFuture<T> ftask = newTaskFor(task, result);
execute(ftask);
return ftask;
}
public <T> Future<T> submit(Callable<T> task) {
if (task == null) throw new NullPointerException();
RunnableFuture<T> ftask = newTaskFor(task);
execute(ftask);
return ftask;
}
addWorker
private boolean addWorker(Runnable firstTask, boolean core) {
// 标号
retry:
// 自旋
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
/*
* 有两种情况可以创建线程，接收新任务，所以才会有以下两个判断
* 1.线程池是runing状态。
* 2.线程池是shutdown状态,但是此时还可以接收工作队列中的任务
*/
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty()))
return false;
// 自旋增加线程数
for (;;) {
int wc = workerCountOf(c);
// 当前工作线程数是否大于允许最大容量
if (wc >= CAPACITY ||
// 当前线程是否是核心线程,是核心线程
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
if (compareAndIncrementWorkerCount(c))
// 退出循环到标号位置
break retry;
c = ctl.get(); // Re-read ctl
// 线程池状态是否已经改变
if (runStateOf(c) != rs)
continue retry;
// else CAS failed due to workerCount change; retry inner loop
}
}
// 线程数增加后，需要创建线程，为了保证原子性且hashMap是非线程安全的，故加锁
boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try {
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 ||
// 这个是shutdown的时候留给执行工作队列的条件
(rs == SHUTDOWN && firstTask == null)) {
// 如果线程已经启动了抛出异常（不是Worker启动的），因为我们还没有调用
if (t.isAlive()) // precheck that t is startable
throw new IllegalThreadStateException();
// 加入线程池，即hashSet中
workers.add(w);
// 记录历史最大的线程数
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
if (workerAdded) {
// 启动线程，内部run方法调用runWorker
t.start();
workerStarted = true;
}
}
} finally {
if (! workerStarted)
// 如果线程启动失败了，需要对应处理
addWorkerFailed(w);
}
return workerStarted;
}
runWorker
// Worker 线程中run调用了 runWorker
public void run() {
runWorker(this);
}
final void runWorker(Worker w) {
// 获取工作线程
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
// 清空初始的任务
w.firstTask = null;
// 将锁状态state由-1改为0，即可以中断，其他线程可以获取改worker
w.unlock(); // allow interrupts
boolean completedAbruptly = true;
try {
// 如果task不为空，则代表工作线程关联的任务还没执行，需要执行。
while (task != null ||
// 线程池中的任务处理完了，才会处理缓冲队列中的任务
// 如果task为空，则从工作队列中获取任务，此处会一直循环，直到工作缓冲队列里面的任务全部执行完
(task = getTask()) != null) {
// 获取任务之后，进行加锁，防止在任务执行期间，其他线程调用了shutdown（只会中断被阻塞挂起的线程）后，正在执行的任务被中断。
w.lock();
//如果池停止，确保线程被中断
if ((runStateAtLeast(ctl.get(), STOP) ||
// 二次操作，重新设置中断标志状态
(Thread.interrupted() &&
runStateAtLeast(ctl.get(), STOP))) &&
!wt.isInterrupted())
// 中断线程
wt.interrupt();
try {
// 空方法，留给自己重写自定义特性的
beforeExecute(wt, task);
Throwable thrown = null;
try {
// 调用任务的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 {
// 空方法，留给自己重写自定义特性的
afterExecute(task, thrown);
}
} finally {
task = null;
w.completedTasks++;
w.unlock();
}
}
// 设置改任务是正常执行完成的
completedAbruptly = false;
} finally {
/*
* 任务执行完成之后，需要做一些操作
* 比如移除hashSet中的Worker，完成任务数的累计、空闲线程的回收，资源的处理等等
*/
processWorkerExit(w, completedAbruptly);
}
}
processWorkerExit
任务完成后，移除对应的工作者，缩小线程池
private void processWorkerExit(Worker w, boolean completedAbruptly) {
// 如果任务不是正常完成的，则将线程池线程数置为0
if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted
// 内部是循环CAS减
decrementWorkerCount();
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
// 累计完成的任务数，移除完成的工作者
completedTaskCount += w.completedTasks;
workers.remove(w);
} finally {
mainLock.unlock();
}
// 尝试终止线程池
tryTerminate();
// 缩小线程池，如果线程池是 RUNNING或者SHUTDOWN状态，则保证至少有一个线程执行任务
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);
}
}
getTask
获取工作队列中的任务，未完待续
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.
// 1.如果池状态为SHUTDOWN，且队列为空，（SHUTDOWN的时候，会把队列任务处理完）
// 2.如果池状态STOP、TYDING、TERMINATE（STOP不在接收与处理任务，会中断正在处理的任务）
if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
// 重置线程池数为0
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;
}
}
}
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