ThreadPoolExecutor
概述
添加任务的流程
步骤 1：检查线程池状态
首先，ThreadPoolExecutor 会检查当前线程池的状态，确保线程池还没有关闭。如果线程池已经关闭，会抛出 RejectedExecutionException。
步骤 2：检查核心线程数
如果线程池的状态正常，ThreadPoolExecutor 会检查当前线程池中的线程数量是否小于核心线程数（corePoolSize）。如果是，会创建一个新的线程来执行任务。
步骤 3：检查任务队列
如果当前线程池中的线程数量已经达到核心线程数，ThreadPoolExecutor 会尝试将任务放入任务队列（workQueue）中。如果任务队列已满，会进入下一步。
步骤 4：检查最大线程数
如果任务队列已满，ThreadPoolExecutor 会检查当前线程池中的线程数量是否小于最大线程数（maximumPoolSize）。如果是，会创建一个新的非核心线程来执行任务。
步骤 5：执行拒绝策略
如果当前线程池中的线程数量已经达到最大线程数，并且任务队列也已满，ThreadPoolExecutor 会调用拒绝策略（RejectedExecutionHandler）来处理这个任务。默认的拒绝策略是 AbortPolicy，它会抛出 RejectedExecutionException。
Worker
Class Worker mainly maintains interrupt control state for threads running tasks, along with other minor bookkeeping.
Worker主要 维护 正在运行的线程的中断控制 及 其他次要的记录；
This class opportunistically extends AbstractQueuedSynchronizer to simplify acquiring and releasing a lock surrounding each task execution.
Worker继承扩展了AQS，目的是 简化获取和释放每个任务执行的锁；
This protects against interrupts that are intended to wake up a worker thread waiting for a task from instead interrupting a task being run.
We implement a simple non-reentrant mutual exclusion lock rather than use ReentrantLock because we do not want worker tasks to be able to reacquire the lock when they invoke pool control methods like setCorePoolSize.
实现了一个 不可重入互斥锁，因为不希望 当调用setCorePoolSize等方法时能够重新获取锁；
Additionally, to suppress interrupts until the thread actually starts running tasks, we initialize lock state to a negative value, and clear it upon start (in runWorker).
executor.execute(Runnable command)
/**
* executor.execute(Runnable command)
*
* java.util.concurrent.ThreadPoolExecutor#execute(java.lang.Runnable)
* public void execute(Runnable command) {
* if (command == null)
* throw new NullPointerException();
*
* int c = ctl.get();
* if (workerCountOf(c) < corePoolSize) { // 如果 正在运行的线程数 < corePoolSize，会开启一个新的core线程执行；
* if (addWorker(command, true)) // 如果 添加&启动新的core线程成功 -> 结束
* return;
* c = ctl.get();
* }
* if (isRunning(c) && workQueue.offer(command)) { // 如果 正在运行的线程数 >= corePoolSize，任务添加至阻塞队列成功
* int recheck = ctl.get();
* if (! isRunning(recheck) && remove(command)) //
* reject(command);
* else if (workerCountOf(recheck) == 0)
* addWorker(null, false); //
* }
* else if (!addWorker(command, false)) // 如果 正在运行的线程数 >= corePoolSize，阻塞队列已满 -> 添加非core线程
* reject(command); // 如果失败 -> 拒绝任务
* }
*
* java.util.concurrent.ThreadPoolExecutor#addWorker(java.lang.Runnable, boolean)
* private boolean addWorker(Runnable firstTask, boolean core) {
* retry:
* 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()))
* return false;
*
* for (;;) {
* int wc = workerCountOf(c);
* if (wc >= CAPACITY ||
* wc >= (core ? corePoolSize : maximumPoolSize))
* return false;
* if (compareAndIncrementWorkerCount(c)) // 如果新增WorkerCount成功 -> break遍历，执行下面的逻辑
* 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); // 构建新的Worker
* 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); // 将Worker添加至workers
* int s = workers.size();
* if (s > largestPoolSize)
* largestPoolSize = s;
* workerAdded = true;
* }
* } finally {
* mainLock.unlock();
* }
* if (workerAdded) {
* t.start(); // 启动线程
* workerStarted = true;
* }
* }
* } finally {
* if (! workerStarted)
* addWorkerFailed(w);
* }
* return workerStarted;
* }
*
*
* java.util.concurrent.ArrayBlockingQueue#offer(java.lang.Object)
*
* java.util.concurrent.ThreadPoolExecutor#reject(java.lang.Runnable)
* final void reject(Runnable command) {
* handler.rejectedExecution(command, this);
* }
*
*/
executor.submit(Runnable task)
/**
* executor.submit(Runnable task)
*
* java.util.concurrent.AbstractExecutorService#submit(java.lang.Runnable)
* public Future<?> submit(Runnable task) {
* if (task == null) throw new NullPointerException();
* RunnableFuture<Void> ftask = newTaskFor(task, null); // 将Runnable封装为FutureTask
* execute(ftask); // 执行任务
* return ftask;
* }
*
* java.util.concurrent.AbstractExecutorService#newTaskFor(java.lang.Runnable, java.lang.Object)
* protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
* return new FutureTask<T>(runnable, value);
* }
*
* java.util.concurrent.FutureTask#FutureTask(java.lang.Runnable, java.lang.Object)
* public FutureTask(Runnable runnable, V result) {
* this.callable = Executors.callable(runnable, result);
* this.state = NEW; // ensure visibility of callable
* }
*
* java.util.concurrent.Executor#execute(java.lang.Runnable)
* java.util.concurrent.ThreadPoolExecutor#execute(java.lang.Runnable)
* 和executor.execute(Runnable command)逻辑一致
*/
executor.submit(Callable<T> task)
/**
* executor.submit(Callable<T> task)
*
* java.util.concurrent.AbstractExecutorService#submit(java.util.concurrent.Callable)
* public <T> Future<T> submit(Callable<T> task) {
* if (task == null) throw new NullPointerException();
* RunnableFuture<T> ftask = newTaskFor(task); // 构建FutureTask
* execute(ftask); // 执行任务
* return ftask;
* }
*
* java.util.concurrent.AbstractExecutorService#newTaskFor(java.util.concurrent.Callable)
* protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
* return new FutureTask<T>(callable);
* }
*
* java.util.concurrent.FutureTask#FutureTask(java.util.concurrent.Callable)
* public FutureTask(Callable<V> callable) {
* if (callable == null)
* throw new NullPointerException();
* this.callable = callable;
* this.state = NEW; // ensure visibility of callable
* }
*
* java.util.concurrent.Executor#execute(java.lang.Runnable)
* java.util.concurrent.ThreadPoolExecutor#execute(java.lang.Runnable)
* 和executor.execute(Runnable command)逻辑一致
*/
runWorker如何被执行？
/**
* runWorker(Worker w) 如何被调用？
*
* 1、无论是 executor.submit(Callable<T> task)、executor.submit(Runnable task)、executor.execute(Runnable command)都会调用java.util.concurrent.ThreadPoolExecutor#execute(java.lang.Runnable)
* 2、在第一步中会调用java.util.concurrent.ThreadPoolExecutor#addWorker(java.lang.Runnable, boolean)， 会将被提交的任务封装为Worker
* a、Worker实现了Runnable，run方法即是Worker实际执行的任务
* b、new Worker时，构造方法中创建了新的线程，Worker的thread指向新的线程；
* c、在ThreadPoolExecutor#execute中，会将Worker指向的thread进行启动，此时将会执行Worker的run方法，run方法内部实现的是java.util.concurrent.ThreadPoolExecutor#runWorker(java.util.concurrent.ThreadPoolExecutor.Worker)
*/
public class ThreadPoolExecutor extends AbstractExecutorService {
private final class Worker extends AbstractQueuedSynchronizer implements Runnable{
final Thread thread;
Runnable firstTask;
Worker(Runnable firstTask) {
setState(-1); // inhibit interrupts until runWorker
this.firstTask = firstTask;
this.thread = getThreadFactory().newThread(this);
}
public void run() {
runWorker(this);
}
public void unlock() { release(1); }
public void lock() { acquire(1); }
protected boolean tryRelease(int unused) {
setExclusiveOwnerThread(null);
setState(0);
return true;
}
protected boolean tryAcquire(int unused) {
if (compareAndSetState(0, 1)) {
setExclusiveOwnerThread(Thread.currentThread());
return true;
}
return false;
}
public ThreadFactory getThreadFactory() {
return threadFactory;
}
}
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
// The queue used for holding tasks and handing off to worker threads.
private final BlockingQueue<Runnable> workQueue;
// Set containing all worker threads in pool. Accessed only when holding mainLock. 包含所有线程的Set，仅持有mainlock访问
private final HashSet<Worker> workers = new HashSet<Worker>();
// Tracks largest attained pool size. Accessed only under mainLock. 达到最大的线程数量，仅持有mainlock访问
private int largestPoolSize;
// Handler called when saturated or shutdown in execute. 当执行时线程池 饱和或关闭 时调用的拒绝策略
private volatile RejectedExecutionHandler handler;
// Timeout in nanoseconds for idle threads waiting for work. 空闲线程生存时间
// Threads use this timeout when there are more than corePoolSize present or if allowCoreThreadTimeOut. 当线程池的线程数量>corePoolSize时被使用
// Otherwise they wait forever for new work.
private volatile long keepAliveTime;
// Core pool size is the minimum number of workers to keep alive (and not allow to time out etc) unless allowCoreThreadTimeOut is set, in which case the minimum is zero.
// 线程池中 最小的保持活着的线程数量
private volatile int corePoolSize;
// Maximum pool size.
private volatile int maximumPoolSize;
// The default rejected execution handler
private static final RejectedExecutionHandler defaultHandler = new java.util.concurrent.ThreadPoolExecutor.AbortPolicy();
// Factory for new threads.
private volatile ThreadFactory threadFactory;
final void runWorker(Worker w) {
}
}
public class Executors {
static class DefaultThreadFactory implements ThreadFactory {
private static final AtomicInteger poolNumber = new AtomicInteger(1);
private final ThreadGroup group;
private final AtomicInteger threadNumber = new AtomicInteger(1);
private final String namePrefix;
DefaultThreadFactory() {
SecurityManager s = System.getSecurityManager();
group = (s != null) ? s.getThreadGroup() :
Thread.currentThread().getThreadGroup();
namePrefix = "pool-" +
poolNumber.getAndIncrement() +
"-thread-";
}
public Thread newThread(Runnable r) {
Thread t = new Thread(group, r, namePrefix + threadNumber.getAndIncrement(), 0);
if (t.isDaemon())
t.setDaemon(false);
if (t.getPriority() != Thread.NORM_PRIORITY)
t.setPriority(Thread.NORM_PRIORITY);
return t;
}
}
public static ThreadFactory defaultThreadFactory() {
return new Executors.DefaultThreadFactory();
}
}
ThreadFactory
构建方式
引入：com.google.guava包
ThreadFactory namedThreadFactory = new ThreadFactoryBuilder().setNameFormat("demo-pool-%d").build();
链路
execute(Runnable command)
// java.util.concurrent.ThreadPoolExecutor.execute add core线程 -> add Queue -> add 非core线程
/**
* Executes the given task sometime in the future.The task may execute in a new thread or in an existing pooled thread.
* 执行给定的任务；可能在 新线程或已存在的线程 中执行；
* @param command
*/
public void execute(Runnable command) {
int c = ctl.get();
// If fewer than corePoolSize threads are running, try to start a new thread with the given command as its first task.
// 如果 运行的线程数 < 核心线程数 -> 创建一个新的core线程执行该任务
if (workerCountOf(c) < corePoolSize) {
if (addWorker(command, true))
return;
c = ctl.get();
}
// 如果 线程数 >= core && 线程池正在运行 && 任务添加队列成功 ->
if (isRunning(c) && workQueue.offer(command)) {
int recheck = ctl.get();
if (! isRunning(recheck) && remove(command))
reject(command);
else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}
// 添加非core线程， 如果失败 -> 拒绝任务
else if (!addWorker(command, false))
reject(command);
}
// java.util.concurrent.ThreadPoolExecutor.addWorker
/**
* Checks if a new worker can be added with respect to current pool state and the given bound (either core or maximum).
* 检测 当前线程池的state和边界，一个新的线程是否能被添加
*/
private boolean addWorker(Runnable firstTask, boolean core) {
retry:
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()))
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); // 将提交的Runnable封装为一个Worker（创建一个新的线程）
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); // 将新建的worker添加到workers
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
if (workerAdded) {
t.start(); // 如果worker创建成功 -> 启动该worker线程
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
}
// java.util.concurrent.ThreadPoolExecutor.Worker.run
public void run() {
runWorker(this);
}
// java.util.concurrent.ThreadPoolExecutor.runWorker
/**
* Main worker run loop. Repeatedly gets tasks from queue and executes them
*/
final void runWorker(Worker w) {
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock(); // allow interrupts // 使用AQS的独占模式释放lock
boolean completedAbruptly = true;
try {
while (task != null || (task = getTask()) != null) {
w.lock(); // 使用AQS的独占模式获取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 {
beforeExecute(wt, task); // 任务执行前
Throwable thrown = null;
try {
task.run(); // 任务执行
} 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); // 任务执行后
}
} finally {
task = null;
w.completedTasks++;
w.unlock(); // 使用AQS的独占模式释放lock
}
}
completedAbruptly = false;
} finally {
processWorkerExit(w, completedAbruptly);
}
}
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