java多线程源码解析
一.interface Executor 最顶层接口
1.1
void execute(Runnable command);
二.class Executors 为这些 Executor 提供了便捷的工厂方法。
1.newFixedThreadPool 固定个数的线程池
public static ExecutorService newFixedThreadPool(int nThreads) { // 1.1 调用ThreadPoolExecutor return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());//1.2 使用linkedBlockingQueue }
1.1 调用ThreadPoolExecutor()构造方法
//1.1.1 参数说明 public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
//1.1.2 调用另一个构造方法
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, Executors.defaultThreadFactory(), defaultHandler); }
1.1.1 参数说明*
corePoolSize 核心线程数
maximumPoolSize 最大线程数
keepAliveTime 线程存活时间
unit
BlockingQueue 队列
1.1.2 调用基础的构造方法
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) { 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; }
没什么好说的，就是一些参数校验，异常处理。
1.2 linkedBlockingQueue
看名字就知道，这是一个阻塞队列。 阻塞队列我会另写文章，此处仅继续往下走 不向上挖。
public LinkedBlockingQueue() { this(Integer.MAX_VALUE);// 1.2.1调用LinkedBlockingQueue(int) 构造方法 }
1.2.1调用LinkedBlockingQueue(int) 构造方法
public LinkedBlockingQueue(int capacity) { if (capacity <= 0) throw new IllegalArgumentException(); this.capacity = capacity; last = head = new Node<E>(null); }
很明显，构造了一个最大整型2的32次方-1的队列
*对于这些参数的含义，我想应该在execute方法中去一探究竟。
先说结论
1.如果正在运行的线程数量小于 corePoolSize，那么马上创建线程运行这个任务；
2.如果正在运行的线程数量大于或等于 corePoolSize，那么将这个任务放入队列。
3.如果这时候队列满了，而且正在运行的线程数量小于 maximumPoolSize，那么还是要创建线程运行这个任务；（此时队列里面的任务还在队列里面，也就是跨过了队列里面的任务，创建了新的线程运行当前任务）
4.如果队列满了，而且正在运行的线程数量大于或等于 maximumPoolSize，那么线程池会抛出异常，告诉调用者“我不能再接受任务了”。
public void execute(Runnable command) {
if (command == null)
throw new NullPointerException();
int c = ctl.get();// 1.1
if (workerCountOf(c) < corePoolSize) {// 当运行线程数小于corePoolSize
if (addWorker(command, true)) // 1.2 addWorker 创建成功则返回，失败则继续
return;
c = ctl.get();
}
if (isRunning(c) && workQueue.offer(command)) { // 1.3 offer() 是向队列添加一个新元素，当队列满返回false，区别于add()也是添加一个新元素，队列满抛出unchecked异常
int recheck = ctl.get();// 二次检查
if (! isRunning(recheck) && remove(command))// 1.4recheck>0, remove 删除任务，返回boolean
reject(command); //拒绝该任务
else if (workerCountOf(recheck) == 0) //1.5 recheck=0时，
addWorker(null, false);
}
else if (!addWorker(command, false))// 添加失败，拒绝
reject(command);
}
1.1 ct1 为-2的29次方, -536870912
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
private static int ctlOf(int rs, int wc) { return rs | wc; }
private static final int RUNNING = -1 << COUNT_BITS;
private static final int COUNT_BITS = Integer.SIZE - 3;
public static final int SIZE = 32;
1.2
private boolean addWorker(Runnable firstTask, boolean core) {
retry:// label标签，可以在循环嵌套时使用，可以在内层循环直接跳出外层循环
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())) // 检查队列是否为空
return false;
for (;;) {
int wc = workerCountOf(c);
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))// 当前运行线程大于等于容量，或者根据core，判断大于等于核心线程数or最大线程数
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;
}
1.3 ctl.get()<0 且队列能成功添加一个新任务
private static final int SHUTDOWN = 0 << COUNT_BITS;
private static boolean isRunning(int c) {
return c < SHUTDOWN;
}
1.4 ctl.get>0 且队列能删除改任务 则拒绝任务
1.5 ctl ==0 , addWorker(null, false)
private static final int CAPACITY = (1 << COUNT_BITS) - 1;
private static int workerCountOf(int c) { return c & CAPACITY; }
2.newSingleThreadExecutor corePoolSize 和maximumPoolSize都为1 的线程池
public static ExecutorService newSingleThreadExecutor() { return new FinalizableDelegatedExecutorService (new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>())); }
3.newCachedThreadPool corePoolSize 为0，maximumPoolSize都为最大整型数的线程池，即都放在队列中
public static ExecutorService newCachedThreadPool() { return new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>());//注意此处为SynchronousQueue,看源码其实是创建了TransferStack() }
4.newScheduledThreadPool
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) { return new ScheduledThreadPoolExecutor(corePoolSize); }
public ScheduledThreadPoolExecutor(int corePoolSize) { super(corePoolSize, Integer.MAX_VALUE, 0, NANOSECONDS, new DelayedWorkQueue());//注意此处为DelayedWorkQueue,初始容量为16的阻塞延迟队列？ }
三.class ThreadPoolExecutor extends AbstractExecutorService 提供一个可扩展的线程池实现
四.interface ExecutorService extends Executor 更广泛的接口
五.abstract class AbstractExecutorService extends ExecutorService
