前一篇博客介绍了构造参数分别是什么意思
现在介绍java线程池源码
1 init
线程池初始化，代码比较简单
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) {
if (corePoolSize < 0 || //核心线程数校验
maximumPoolSize <= 0 || //非核心线程数校验
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null) //必传参数校验
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;
}
2 线程池核心类Worker
线城池中，使用Worker来保证线程池线程的活跃，保证在没有任务执行时，也能保证线程资源不被释放掉
woker类实现了runable接口，本身就是一个线程
private final class Worker
extends AbstractQueuedSynchronizer
implements Runnable
{
private static final long serialVersionUID = 6138294804551838833L;
//worker运行的线程，是线程池中实际的线程，通过ThreadFactory生成
final Thread thread;
//线程池新增线程时的默认任务，可以为空
Runnable firstTask;
//已经执行过的线程任务数
volatile long completedTasks;
Worker(Runnable firstTask) {
setState(-1); // inhibit interrupts until runWorker
this.firstTask = firstTask;
this.thread = getThreadFactory().newThread(this);
}
//将执行方法委托给ThreadPoolExecuter
public void run() {
runWorker(this);
}
// Lock methods
//
// The value 0 represents the unlocked state.
// The value 1 represents the locked state.
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) {
}
}
}
}3 线程池新增任务
下面看源码
核心方法1 ThreadPoolExecuter.execute()
public void execute(Runnable command) {
if (command == null)
throw new NullPointerException();
int c = ctl.get();
//判断当前线程数量和最大核心线程数
if (workerCountOf(c) < corePoolSize) {//线程数<最大核心线程数
if (addWorker(command, true))//尝试创建新的worker，如果创建成功则直接返回
return;
c = ctl.get();//获取最新的的数量
}
if (isRunning(c) && workQueue.offer(command)) {//1 检查线程池状态
//2当前线程数>=最大核心线程数。
//3尝试将新增的线程放入blockingqueue
int recheck = ctl.get(); //对线程池状态进行二次校验，防止其他线程在offer期间对线程池状态进行了修改
if (! isRunning(recheck) && remove(command)) //二次校验，失败后将新增线程从blockingqueue移除
//二次校验成功则不移除，利用java&&的特性
reject(command); //校验失败进入过载策略
else if (workerCountOf(recheck) == 0) //二次校验成功，判断当前线程池线程数量是否归零，
//如果归零，则创建新的空worker，由worker去进行处理queue
//中的任务
addWorker(null, false);
}
else if (!addWorker(command, false))//如果queue.offer返回false，证明queue已经满了，
// 尝试创建非核心线程
reject(command); //创建失败则证明已经到达最大线程数，进去过载策略
}2 核心方法二 ThreadPoolExecuter.addWorker（）
private boolean addWorker(Runnable firstTask, boolean core) {
retry:
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);//获取当前线程池状态
// Check if queue empty only if necessary.
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty()))
return false;
for (;;) {
int wc = workerCountOf(c);
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
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 {
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();
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
if (workerAdded) {
t.start();
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
}