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Java线程池ThreadPoolExecutor源码解析

發(fā)布時(shí)間：2023/12/29 java 36 coder

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Java線程池ThreadPoolExecutor源碼解析

1.ThreadPoolExecutor的構(gòu)造實(shí)現(xiàn)

以jdk8為準(zhǔn)，常說線程池有七大參數(shù)，通常而言，有四個(gè)參數(shù)是比較重要的

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

corePoolSize:核心線程數(shù),具體含義理解代碼
maximumPoolSize:最大線程數(shù)
keepAliveTime:線程空閑的存活時(shí)間
unit:時(shí)間單位
BlockingQueue:阻塞隊(duì)列,用來保存等待執(zhí)行的任務(wù)

接下來去看完整參數(shù)的構(gòu)造實(shí)現(xiàn):

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;
    }

ThreadFactory:線程工廠,用來創(chuàng)造線程

RejectedExecutionHandler:拒絕策略

如果核心線程數(shù)等其他參數(shù)非法化就會(huì)拋出相應(yīng)的異常

 if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();

之后進(jìn)行初始化賦值

 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;

注:acc是一個(gè)成員變量,用來管理線程池中線程的訪問控制上下文,其實(shí)現(xiàn)類是AccessControlContext

2.線程池的執(zhí)行execute

public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();
        
        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);
    }

總共大致分為三步:要想理解線程池的執(zhí)行,要先去理解控制字段其具體含義

private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
private static final int COUNT_BITS = Integer.SIZE - 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; }

先聲明線程池的五種狀態(tài),再看其他字段方法具體執(zhí)行了其他什么操作

RUNNING: -1 << COUNT_BITS，即高3位為111
SHUTDOWN: 0 << COUNT_BITS，即高3位為000
STOP : 1 << COUNT_BITS，即高3位為001
TIDYING : 2 << COUNT_BITS,即高3位為010
TERMINATED: 3 << COUNT_BITS,即高3位為011

至于其每種空置狀態(tài)的具體意義,根據(jù)英文釋義結(jié)合代碼具體理解,而非直接理解,通過位移位的操作將高3位與低29位分離開來,高三位表示此時(shí)整個(gè)線程池的運(yùn)行狀態(tài),低29位表示線程池中線程的數(shù)量,再去看execute執(zhí)行過程即可.

int c = ctl.get(); 
if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }

用于獲取此時(shí)線程中的線程數(shù),如果小于核心線程數(shù),就添加任務(wù),添加任務(wù)成功則返回,失敗則重新獲取控制字段,addworker后續(xù)了解,復(fù)雜的東西簡(jiǎn)單化,理解大致操作思想最為核心.

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);
        }

根據(jù)控制字段c去判斷線程池的運(yùn)行狀態(tài)是否正在運(yùn)行,如果添加任務(wù)成功則不會(huì)執(zhí)行失敗,或者說此時(shí)線程數(shù)有可能已經(jīng)大于了核心線程數(shù)也有可能走到這,所以會(huì)將任務(wù)添加到阻塞隊(duì)列中去,然后重新去獲得控制字段,再去做校驗(yàn),如果此時(shí)線程池不是正在運(yùn)行的狀態(tài)并且刪除任務(wù)成功,這一步主要是為了防止阻塞隊(duì)列添加任務(wù)成功這個(gè)過程,可能線程池不運(yùn)行了,那么這時(shí)候就需要將添加的那個(gè)任務(wù)刪除,并對(duì)他執(zhí)行拒絕策略,又或者是此時(shí)線程池中的線程數(shù)已經(jīng)為0,說明沒有線程在工作了,因此添加一個(gè)空任務(wù),至于第二個(gè)參數(shù)在addWorker中在做說明

else if (!addWorker(command, false))
            reject(command);

字面意思就是添加任務(wù)失敗,執(zhí)行拒絕策略,則是為了應(yīng)對(duì)線程池已經(jīng)到了滿負(fù)載的狀態(tài)

3.線程池的任務(wù)添加addworker

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;
    }

代碼量很長(zhǎng),但是大致可分為兩部分,且邏輯很清晰

這里使用了標(biāo)簽語法,前半段大致是是否需要添加線程做一系列準(zhǔn)備
```
 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
            }
        }
```
1. 獲取控制字段c:這個(gè)字段包含了運(yùn)行狀態(tài)信息和線程池?cái)?shù)量信息,是一個(gè)復(fù)合字段,而rs則是獲取高三位的線程池狀態(tài)信息
2. 根據(jù)前面線程池狀態(tài)信息,運(yùn)行RUNNING值最小,因此判斷線程池如果處于非運(yùn)行的狀態(tài),則去判斷是否處于關(guān)閉的狀態(tài),判斷第一個(gè)任務(wù)是否為空,隊(duì)列不為空,但是由于前面取反操作,其真正含義是:如果線程池的狀態(tài)不是 SHUTDOWN，或者任務(wù)隊(duì)列為空，或者有待執(zhí)行的任務(wù)，那么就不會(huì)拒絕新任務(wù)的提交,否則就返回false,表示添加任務(wù)失敗
3. 接下來死循環(huán)表示需要去添加執(zhí)行的任務(wù),首先獲取線程池中的線程數(shù),關(guān)鍵的地方在這,如果此時(shí)的線程數(shù)大于等于容量或者(這里根據(jù)傳遞的參數(shù)core來選則比較的目標(biāo)是核心線程數(shù)還是最大線程數(shù)),比較失敗,則說明超過了接受的范疇,添加任務(wù)失敗,如果沒有失敗,則通過底層CAS操作使得線程數(shù)加1,然后直接結(jié)束調(diào)用,跳出循環(huán),,如果CAS失敗,則說明ctl字段受到了變化,此期間有其他任務(wù)參與,重新獲取此字段,去判斷一下重新獲取的ctl字段和之前的rs字段是否相等,這是為了保障多線程情況下出現(xiàn)的一種并發(fā)競(jìng)爭(zhēng)問題導(dǎo)致的線程數(shù)發(fā)生錯(cuò)亂.
至此,上半部分的核心已經(jīng)解決,下半部分此時(shí)真正去實(shí)現(xiàn)任務(wù)的添加,通過線程池中的內(nèi)部類Worker去實(shí)現(xiàn)
```
  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. 兩個(gè)布爾類型暫時(shí)不用管,大致猜測(cè)意思即可,將firstask任務(wù)交付給worker,由worker內(nèi)部的thread線程去執(zhí)行,因此需要去理解worker的實(shí)現(xiàn)
  
  3.1Worker內(nèi)部的工作者
  
  3.11構(gòu)造方法實(shí)現(xiàn)
```
Worker(Runnable firstTask) {
    setState(-1); // inhibit interrupts until runWorker
    this.firstTask = firstTask;
    this.thread = getThreadFactory().newThread(this);
}
```
  接收一個(gè)Runnable參數(shù)做為任務(wù)進(jìn)行初始化,這里用到了AQS的一些實(shí)現(xiàn),然后通過線程工廠創(chuàng)造一個(gè)新的線程,賦予給內(nèi)部的成員變量引用
  - 還有一些鎖的一些操作,后續(xù)再看
2. 如果工作者的內(nèi)部線程已經(jīng)被創(chuàng)造好,實(shí)現(xiàn)就緒,要先獲得線程池的互斥鎖,然后對(duì)接下來的操作進(jìn)行互斥訪問
3. 重新獲取最新的線程池的運(yùn)行狀態(tài),只有當(dāng)線程池處于運(yùn)行狀態(tài)或者處于關(guān)閉狀態(tài)但沒有待執(zhí)行的任務(wù)時(shí)，才能將新工作線程添加到線程池中,也就是worker中去,因此一個(gè)worker內(nèi)部具備一個(gè)thread,如果想要實(shí)現(xiàn)許多線程去完成線程池的相應(yīng)操作,需要將worker封裝成集合,因此線程池內(nèi)部還有一成員變量:
```
private final HashSet<Worker> workers = new HashSet<Worker>();
```
  這樣就確保了每一個(gè)worker都是獨(dú)一無二的,不會(huì)重復(fù)的,也就意味著每一個(gè)線程都不一樣.
4. 而最后一個(gè)largestPoolSize則是保留歷史的最大線程數(shù)的,用來記錄,至此就已經(jīng)添加成功了,只不過此時(shí)還沒有執(zhí)行
5. 之后解鎖,用之前標(biāo)志位workerAdded表示添加成功,然后啟動(dòng)線程,也就是去執(zhí)行這個(gè)任務(wù),再用另一個(gè)標(biāo)志workerStarted表示啟動(dòng)成功.
6. 最后則是檢查是否有什么異常在啟動(dòng)期間,如果沒啟動(dòng)成功,則調(diào)用addWorkerFiled方法去處理
  
  3.12 addWorkerFailed方法
```
private void addWorkerFailed(Worker w) {
    final ReentrantLock mainLock = this.mainLock;
    mainLock.lock();
    try {
        if (w != null)
            workers.remove(w);
        decrementWorkerCount();
        tryTerminate();
    } finally {
        mainLock.unlock();
    }
}
```
  - 緊接上文,也就是啟動(dòng)失敗的話,會(huì)將執(zhí)行任務(wù)的workerremove(底層通過HashMap實(shí)現(xiàn)鍵的刪除),然后減少線程數(shù),等待一會(huì),這個(gè)過程是互斥的,因?yàn)闋砍兜娇刂谱侄?/li>
7. 至此,添加任務(wù)如果成功,則進(jìn)行執(zhí)行,如果成功開啟執(zhí)行,則成功返回
因此,根據(jù)線程池的執(zhí)行添加流程,大致可以將此過程通過繪圖的方式表現(xiàn)出來:

4.工作者的run方法是如何運(yùn)行的

在worker中還有一個(gè)方法

  public void run() {
            runWorker(this);
        }

是其執(zhí)行的具體操作

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);
        }
    }

上鎖之前的操作都很容易看懂,處了getTask,這個(gè)方法用來獲取阻塞隊(duì)列中的任務(wù),后續(xù)再理解
1. 首先看第一段if,就是用來查看此時(shí)線程池的狀態(tài),如果不處于關(guān)閉或者運(yùn)行的狀態(tài),或者線程處于中斷的狀態(tài),則確保線程中斷
2. 接下來是一部分異常和錯(cuò)誤的處理以及執(zhí)行一些前置任務(wù)和一些后置任務(wù)
3. 最后完成的任務(wù)數(shù)加一,解鎖,將標(biāo)志位是否中斷,改為false,表示執(zhí)行成功.

5.獲取任務(wù)的getTask方法

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.
        if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
            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;
        }
    }
}

首先標(biāo)志位用來判斷是否超時(shí)，默認(rèn)情況下不超時(shí)，跟之前的參數(shù)掛鉤，后續(xù)再看，然后進(jìn)入死循環(huán)，不斷循環(huán)去執(zhí)行后續(xù)操作
獲取控制位c和rs運(yùn)行狀態(tài)，之后的if操作含義是如果線程池處于關(guān)閉的狀態(tài)或者此時(shí)隊(duì)列為空，就說明沒有任務(wù)需要處理了，此時(shí)讓線程池中的線程數(shù)減一，返回，另一種情況則是線程池的狀態(tài)處于關(guān)閉狀態(tài)之上，則說明線程池現(xiàn)在不執(zhí)行任務(wù)了，不需要管隊(duì)列中是否還有任務(wù)存在，則同上減一，返回。
然后重新獲取線程池的線程數(shù)，接下來的time布爾這個(gè)字段有些作用，后面的allowCoreThreadTimeOut是一個(gè)控制字段,用來表示線程是否允許超時(shí)而返回的一個(gè)字段,如:線程池中的核心線程如果因?yàn)殚L(zhǎng)時(shí)間沒有得到任務(wù)的滋養(yǎng),就如同線程之間會(huì)發(fā)生饑餓一樣,因此存在一個(gè)字段用來控制超時(shí)是否生效.因此如果線程數(shù)大于核心線程數(shù)或者開啟超時(shí)控制字段,就說明會(huì)執(zhí)行超時(shí)退出.
接下來的if判斷是用來執(zhí)行遞減線程數(shù)的一個(gè)操作,底層采取CAS就不多說了,wc > maximumPoolSize:用來表示如果大于了最大線程數(shù),說明需要減少線程數(shù),至于為什么會(huì)出現(xiàn)這種情況,等會(huì)理解.(timed && timedOut):說明開啟超時(shí)退出,且上一次獲取任務(wù)因超時(shí)返回,這個(gè)需看后面代碼理解.上面的兩個(gè)條件滿足其中之一即可.wc > 1 || workQueue.isEmpty())而這個(gè)操作則是為了減少不必要的線程開銷,如果阻塞隊(duì)列為空說明沒有任務(wù),那自然不需要多余的線程數(shù)去執(zhí)行,因此會(huì)發(fā)生接下來的操作,遞減線程數(shù),然后跳到下一次循環(huán).
之后接下來就是從阻塞隊(duì)列中獲取任務(wù)的核心了,第一步是根據(jù)超時(shí)控制字段來決定行為方式,允許超時(shí)退出的話,通過poll方式,不允許則通過take方式,兩種方式大致是一個(gè)等待一定時(shí)間,如果為空是前提.另一個(gè)是無限等待,會(huì)阻塞線程.其具體實(shí)現(xiàn)通過阻塞隊(duì)列的真正實(shí)現(xiàn)類別去實(shí)現(xiàn).如果獲取到了任務(wù),就返回,如果沒有則timeout設(shè)置為true,表示沒有接受到任務(wù),因此前文的timeout就理解了.

通常而言線程池中的線程數(shù)是不允許超過最大線程數(shù)的,但通常而言這是一種機(jī)制的完整性和規(guī)范,假如是自定義線程池的情況下,就有可能出現(xiàn)這種情況,另外一種是本人推測(cè)雖然由于增加工作線程數(shù)的操作底層是通過CAS去實(shí)現(xiàn)的,底層是原子性的,同時(shí)進(jìn)行CAS操作就有可能導(dǎo)致ABA問題出現(xiàn),或者操作失敗,或者不斷自旋的可能,

6.任務(wù)的提交submit

眾所周知,任務(wù)需要進(jìn)行提交給線程池,再有線程池去執(zhí)行,而Runnable接口實(shí)現(xiàn)的run方法是沒有返回值的,而在線程中Callable通常具備返回值,且配備Future去接受結(jié)果.因此submit具備不同的操作

這里以AbstractExecutorService(線程池的父類)接口為例:

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;
    }

RunnableFuture接口的實(shí)現(xiàn)類FutureTask,總而言之就是轉(zhuǎn)換為一個(gè)Runnable,然后進(jìn)行提交,最后返回一個(gè)future,至于FutureTask具體內(nèi)容自行詳解.

7.線程池的關(guān)閉

public void shutdown() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            checkShutdownAccess();
            advanceRunState(SHUTDOWN);
            interruptIdleWorkers();
            onShutdown(); // hook for ScheduledThreadPoolExecutor
        } finally {
            mainLock.unlock();
        }
        tryTerminate();
    }

實(shí)現(xiàn)邏輯也很清楚,檢查是否可以關(guān)閉線程,然后設(shè)置線程的狀態(tài),interruptIdleWorkers()這個(gè)方法算是關(guān)鍵的,他會(huì)去中斷worker;onShutdown是一個(gè)空方法,留給子類去實(shí)現(xiàn)的.

 private void interruptIdleWorkers() {
        interruptIdleWorkers(false);
    }

private void interruptIdleWorkers(boolean onlyOne) {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (Worker w : workers) {
                Thread t = w.thread;
                if (!t.isInterrupted() && w.tryLock()) {
                    try {
                        t.interrupt();
                    } catch (SecurityException ignore) {
                    } finally {
                        w.unlock();
                    }
                }
                if (onlyOne)
                    break;
            }
        } finally {
            mainLock.unlock();
        }
    }

他會(huì)去遍歷集合workers,獲取每一個(gè)worker的工作線程,然后嘗試去中斷,最后結(jié)束.

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