ThreadPoolExecutor

梦里梦外; 2021-12-21 05:55 234阅读 0赞

类图  
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Executor 接口

public interface Executor {
    
        /**
         * Executes the given command at some time in the future.  The command
         * may execute in a new thread, in a pooled thread, or in the calling
         * thread, at the discretion of the {@code Executor} implementation.
         *
         * @param command the runnable task
         * @throws RejectedExecutionException if this task cannot be
         * accepted for execution
         * @throws NullPointerException if command is null
         */
        void execute(Runnable command);
    }

## 创建线程池 ##

Executors

return new ThreadPoolExecutor(nThreads, nThreads,
                                          0L, TimeUnit.MILLISECONDS,
                                          new LinkedBlockingQueue<Runnable>());

ThreadPoolExecutor构造器

public ThreadPoolExecutor(int corePoolSize,
                                  int maximumPoolSize,
                                  long keepAliveTime,
                                  TimeUnit unit,
                                  BlockingQueue<Runnable> workQueue) {
            this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
                 Executors.defaultThreadFactory(), defaultHandler);
        }
    
        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.corePoolSize = corePoolSize;
            this.maximumPoolSize = maximumPoolSize;
            this.workQueue = workQueue;
            this.keepAliveTime = unit.toNanos(keepAliveTime);
            this.threadFactory = threadFactory;
            this.handler = handler;
        }

默认线程工厂  
Executors

public static ThreadFactory defaultThreadFactory() {
            return new DefaultThreadFactory();
        }
    
        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;
            }
        }

ThreadFactory 工厂接口

public interface ThreadFactory {
    
        /**
         * Constructs a new {@code Thread}.  Implementations may also initialize
         * priority, name, daemon status, {@code ThreadGroup}, etc.
         *
         * @param r a runnable to be executed by new thread instance
         * @return constructed thread, or {@code null} if the request to
         *         create a thread is rejected
         */
        Thread newThread(Runnable r);
    }

默认拒绝策略  
ThreadPoolExecutor

private static final RejectedExecutionHandler defaultHandler =
            new AbortPolicy();
    
        public static class AbortPolicy implements RejectedExecutionHandler {
            /**
             * Creates an {@code AbortPolicy}.
             */
            public AbortPolicy() { }
    
            /**
             * Always throws RejectedExecutionException.
             *
             * @param r the runnable task requested to be executed
             * @param e the executor attempting to execute this task
             * @throws RejectedExecutionException always
             */
            public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
                throw new RejectedExecutionException("Task " + r.toString() +
                                                     " rejected from " +
                                                     e.toString());
            }
        }

拒绝策略接口RejectedExecutionHandler

public interface RejectedExecutionHandler {
    
        /**
         * Method that may be invoked by a {@link ThreadPoolExecutor} when
         * {@link ThreadPoolExecutor#execute execute} cannot accept a
         * task.  This may occur when no more threads or queue slots are
         * available because their bounds would be exceeded, or upon
         * shutdown of the Executor.
         *
         * <p>In the absence of other alternatives, the method may throw
         * an unchecked {@link RejectedExecutionException}, which will be
         * propagated to the caller of {@code execute}.
         *
         * @param r the runnable task requested to be executed
         * @param executor the executor attempting to execute this task
         * @throws RejectedExecutionException if there is no remedy
         */
        void rejectedExecution(Runnable r, ThreadPoolExecutor executor);
    }

## 添加线程任务 ##

## 1，创建线程任务 ##

AbstractExecutorService

public Future<?> submit(Runnable task) {
            if (task == null) throw new NullPointerException();
            RunnableFuture<Void> ftask = newTaskFor(task, null);
            execute(ftask);
            return ftask;
        }
        
        protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
            return new FutureTask<T>(runnable, value);
        }

FutureTask  
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private static final int NEW          = 0;
        private static final int COMPLETING   = 1;
        private static final int NORMAL       = 2;
        private static final int EXCEPTIONAL  = 3;
        private static final int CANCELLED    = 4;
        private static final int INTERRUPTING = 5;
        private static final int INTERRUPTED  = 6;
        
        /** The underlying callable; nulled out after running */
        private Callable<V> callable;
        
        public FutureTask(Runnable runnable, V result) {
            this.callable = Executors.callable(runnable, result);
            this.state = NEW;       // ensure visibility of callable
        }

Executors

public static <T> Callable<T> callable(Runnable task, T result) {
            if (task == null)
                throw new NullPointerException();
            return new RunnableAdapter<T>(task, result);
        }
    
        static final class RunnableAdapter<T> implements Callable<T> {
            final Runnable task;
            final T result;
            RunnableAdapter(Runnable task, T result) {
                this.task = task;
                this.result = result;
            }
            public T call() {
                task.run();
                return result;
            }
        }

## 2，执行线程任务 ##

ThreadPoolExecutor实现execute方法

private static final int COUNT_BITS = Integer.SIZE - 3;//32-3
        private static final int CAPACITY   = (1 << COUNT_BITS) - 1;
    
        // runState is stored in the high-order bits
        private static final int RUNNING    = -1 << COUNT_BITS;
        private static final int SHUTDOWN   =  0 << COUNT_BITS;
        private static final int STOP       =  1 << COUNT_BITS;
        private static final int TIDYING    =  2 << COUNT_BITS;
        private static final int TERMINATED =  3 << COUNT_BITS;
    
        // Packing and unpacking ctl
        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; }
            
        public void execute(Runnable command) {
            if (command == null)
                throw new NullPointerException();
            /*
             * Proceed in 3 steps:
             *
             * 1. If fewer than corePoolSize threads are running, try to
             * start a new thread with the given command as its first
             * task.  The call to addWorker atomically checks runState and
             * workerCount, and so prevents false alarms that would add
             * threads when it shouldn't, by returning false.
             *
             * 2. If a task can be successfully queued, then we still need
             * to double-check whether we should have added a thread
             * (because existing ones died since last checking) or that
             * the pool shut down since entry into this method. So we
             * recheck state and if necessary roll back the enqueuing if
             * stopped, or start a new thread if there are none.
             *
             * 3. If we cannot queue task, then we try to add a new
             * thread.  If it fails, we know we are shut down or saturated
             * and so reject the task.
             */
            int c = ctl.get();
            if (workerCountOf(c) < corePoolSize) {
                if (addWorker(command, true))
                    return;
                c = ctl.get();
            }
            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);
            }
            else if (!addWorker(command, false))
                reject(command);
        }

添加任务，使用锁，添加成功到Worker的set集合，就执行任务，  
ThreadPoolExecutor

private final HashSet<Worker> workers = new HashSet<Worker>();
        
        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);
                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;
        }

ThreadPoolExecutor内部类Worker，也是用到了aqs，同时是runnable接口

private final class Worker
            extends AbstractQueuedSynchronizer
            implements Runnable
        {
            /**
             * This class will never be serialized, but we provide a
             * serialVersionUID to suppress a javac warning.
             */
            private static final long serialVersionUID = 6138294804551838833L;
    
            /** Thread this worker is running in.  Null if factory fails. */
            final Thread thread;
            /** Initial task to run.  Possibly null. */
            Runnable firstTask;
            /** Per-thread task counter */
            volatile long completedTasks;
    
            /**
             * Creates with given first task and thread from ThreadFactory.
             * @param firstTask the first task (null if none)
             */
            Worker(Runnable firstTask) {
                setState(-1); // inhibit interrupts until runWorker
                this.firstTask = firstTask;
                this.thread = getThreadFactory().newThread(this);
            }
    
            /** Delegates main run loop to outer runWorker  */
            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) {
                    }
                }
            }
        }

运行任务t.start();  
执行worker的run方法，调用firstTask的run方法

final void runWorker(Worker w) {
            Thread wt = Thread.currentThread();
            Runnable task = w.firstTask;
            w.firstTask = null;
            w.unlock(); // allow interrupts
            boolean completedAbruptly = true;
            try {
                while (task != null || (task = getTask()) != null) {
                    w.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);
                        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 {
                processWorkerExit(w, completedAbruptly);
            }
        }

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