先上類圖:
各級(jí)類功能瀏覽
- Executors
工廠類河狐,負(fù)責(zé)創(chuàng)建各式各樣的Threadpoolexecutors出來
public static ExecutorService newFixedThreadPool(int nThreads)
public static ExecutorService newSingleThreadExecutor()
public static ExecutorService newCachedThreadPool()
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize)
- Executor
public interface Executor {
// 一個(gè)抽象方法
void execute(Runnable command);
}
- ExecutorService
增加一寫生命周期管理,任務(wù)提交增強(qiáng)處理等api。
public interface ExecutorService extends Executor {
void shutdown();
List<Runnable> shutdownNow();
boolean isShutdown();
boolean isTerminated();
boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException;
<T> Future<T> submit(Callable<T> task);
<T> Future<T> submit(Runnable task, T result);
Future<?> submit(Runnable task);
<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException;
<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException;
<T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException;
<T> T invokeAny(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
}
- AbstractExecutorService
提供了invokeAny, invokeAll,submit等方法的默認(rèn)實(shí)現(xiàn)馋艺。
- ScheduledExecutorService
提供了兩個(gè)叼逼定時(shí)任務(wù)方法栅干,一看就很親切
public <V> ScheduledFuture<V> schedule(Callable<V> callable,
long delay, TimeUnit unit);
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
long initialDelay,
long period,
TimeUnit unit);
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
long initialDelay,
long delay,
TimeUnit unit);
}
- ThreadPoolExecutor
這個(gè)叼逼在最后慢慢介紹
DelegatedExecutorService(圖是扣的,這筆我不認(rèn)識(shí)捐祠。碱鳞。。踱蛀。)
ThreadFactory
jdk提供的線程創(chuàng)建接口
有自己的默認(rèn)實(shí)現(xiàn)DefaultThreadFactory窿给,只是在創(chuàng)建線程時(shí)為線程添加了命名等。我們可以自己實(shí)現(xiàn)該接口實(shí)現(xiàn)自定義的任何創(chuàng)建線程的方法率拒。創(chuàng)建線程池時(shí)我們可以自定義填大。
- 圖中沒有,不得不提一下RunnableFuture這個(gè)類
public interface RunnableFuture<V> extends Runnable, Future<V> {
void run();
}
異步獲取線程池里線程執(zhí)行結(jié)果就靠他了G伍佟允华!
ThreadPoolExecutor規(guī)則
corePoolSize與maximumPoolSize 由于ThreadPoolExecutor 將根據(jù) corePoolSize和 maximumPoolSize設(shè)置的邊界自動(dòng)調(diào)整池大小,當(dāng)新任務(wù)在方法 execute(java.lang.Runnable) 中提交時(shí):
×绕(1)如果運(yùn)行的線程少于 corePoolSize靴寂,則創(chuàng)建新線程來處理請(qǐng)求,即使其他輔助線程是空閑的召耘;
“倬妗(2)如果設(shè)置的corePoolSize 和 maximumPoolSize相同,則創(chuàng)建的線程池是大小固定的污它,如果運(yùn)行的線程與corePoolSize相同剖踊,當(dāng)有新請(qǐng)求過來時(shí),若workQueue未滿衫贬,則將請(qǐng)求放入workQueue中德澈,等待有空閑的線程去從workQueue中取任務(wù)并處理
(3)如果運(yùn)行的線程多于 corePoolSize 而少于 maximumPoolSize固惯,則僅當(dāng)隊(duì)列滿時(shí)才創(chuàng)建新線程才創(chuàng)建新的線程去處理請(qǐng)求梆造;
(4)如果運(yùn)行的線程多于corePoolSize 并且等于maximumPoolSize葬毫,若隊(duì)列已經(jīng)滿了镇辉,則通過handler所指定的策略來處理新請(qǐng)求纵诞;
∠敖佟(5)如果將 maximumPoolSize 設(shè)置為基本的無界值(如 Integer.MAX_VALUE),則允許池適應(yīng)任意數(shù)量的并發(fā)任務(wù)
也就是說损敷,處理任務(wù)的優(yōu)先級(jí)為:
±谜(1) 核心線程corePoolSize > 任務(wù)隊(duì)列workQueue > 最大線程maximumPoolSize屹逛,如果三者都滿了础废,使用handler處理被拒絕的任務(wù)。
〖逶础(2)當(dāng)池中的線程數(shù)大于corePoolSize的時(shí)候色迂,多余的線程會(huì)等待keepAliveTime長(zhǎng)的時(shí)間,如果無請(qǐng)求可處理就自行銷毀手销。cache線程池使用SynchronousQueue歇僧,fixed使用LinkedBlockingQueue
區(qū)別:
a) cache,創(chuàng)業(yè)公司有特別多的活要干,那就有一個(gè)活來現(xiàn)在的人沒時(shí)間認(rèn)領(lǐng)就去招聘一個(gè)新人锋拖,后來活干完了少了诈悍,招聘進(jìn)來的人閑了,閑下來超過xxx時(shí)間后又把他們開除了兽埃。
b) fixed,創(chuàng)業(yè)公司有特別多的活要干侥钳,但是公司就這么幾個(gè)人,有任務(wù)來就排期吧柄错,反正這幾個(gè)人一個(gè)個(gè)處理舷夺。。售貌。给猾。隊(duì)列滿了之后的應(yīng)對(duì)策略(rejecthanlder)
a) 直接拋棄
b) 拋出異常
c) 主線程執(zhí)行
d) 將最老的線程踢出去,把這個(gè)線程放入隊(duì)列颂跨。
ThreadPoolExecutor源碼
1.小技巧敢伸,把線程數(shù)和線程池狀態(tài)存在一個(gè)原子整數(shù)中,通過cas原子更新
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
低29位存線程數(shù)恒削,高3位存runState(線程池生命周期),這樣runState有5個(gè)值,但是出于簡(jiǎn)單就考慮以下三個(gè)值:
RUNNING狀態(tài):線程池正常運(yùn)行池颈,可以接受新的任務(wù)并處理隊(duì)列中的任務(wù);
SHUTDOWN狀態(tài):不再接受新的任務(wù)钓丰,但是會(huì)執(zhí)行隊(duì)列中的任務(wù)躯砰;
STOP狀態(tài):不再接受新任務(wù),不處理隊(duì)列中的任務(wù)
提供幾個(gè)工具函數(shù)針對(duì)gictl這個(gè)變量操作:
/**
* 這個(gè)方法用于取出runState的值 因?yàn)镃APACITY值為:00011111111111111111111111111111
* ~為按位取反操作斑粱,則~CAPACITY值為:11100000000000000000000000000000
* 再同參數(shù)做&操作弃揽,就將低29位置0了,而高3位還是保持原先的值则北,也就是runState的值
*
* @param c
* 該參數(shù)為存儲(chǔ)runState和workerCount的int值
* @return runState的值
*/
private static int runStateOf(int c) {
return c & ~CAPACITY;
}
/**
* 這個(gè)方法用于取出workerCount的值
* 因?yàn)镃APACITY值為:00011111111111111111111111111111,所以&操作將參數(shù)的高3位置0了
* 保留參數(shù)的低29位痕慢,也就是workerCount的值
*
* @param c
* ctl, 存儲(chǔ)runState和workerCount的int值
* @return workerCount的值
*/
private static int workerCountOf(int c) {
return c & CAPACITY;
}
/**
* 將runState和workerCount存到同一個(gè)int中
* “|”運(yùn)算的意思是尚揣,假設(shè)rs的值是101000,wc的值是000111掖举,則他們位或運(yùn)算的值為101111
*
* @param rs
* runState移位過后的值快骗,負(fù)責(zé)填充返回值的高3位
* @param wc
* workerCount移位過后的值,負(fù)責(zé)填充返回值的低29位
* @return 兩者或運(yùn)算過后的值
*/
private static int ctlOf(int rs, int wc) {
return rs | wc;
}
// 只有RUNNING狀態(tài)會(huì)小于0
private static boolean isRunning(int c) {
return c < SHUTDOWN;
}
2. Worker
實(shí)現(xiàn)了互斥鎖但不可重入,所以沒有使用ReentrantLock方篮。
貼重要代碼:
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;
// 真正執(zhí)行的線程
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;
}
// 實(shí)現(xiàn)不可重入的互斥鎖
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(); }
}
3.開始從execute方法進(jìn)入
活動(dòng)線程小于corePoolSize的時(shí)候創(chuàng)建新的線程名秀;
活動(dòng)線程大于corePoolSize時(shí)都是先加入到任務(wù)隊(duì)列當(dāng)中;
任務(wù)隊(duì)列滿了再去啟動(dòng)新的線程藕溅,如果線程數(shù)達(dá)到最大值就拒絕任務(wù)匕得。
public void execute(Runnable command) {
if (command == null)
throw new NullPointerException();
int c = ctl.get();
// 活動(dòng)線程數(shù) < corePoolSize
if (workerCountOf(c) < corePoolSize) {
// 直接啟動(dòng)新的線程。第二個(gè)參數(shù)true:addWorker中會(huì)重新檢查workerCount是否小于corePoolSize
if (addWorker(command, true))
// 添加成功返回
return;
c = ctl.get();
}
// 活動(dòng)線程數(shù) >= corePoolSize
// runState為RUNNING && 隊(duì)列未滿
if (isRunning(c) && workQueue.offer(command)) {
int recheck = ctl.get();
// double check
// 非RUNNING狀態(tài) 則從workQueue中移除任務(wù)并拒絕
if (!isRunning(recheck) && remove(command))
reject(command);// 采用線程池指定的策略拒絕任務(wù)
// 線程池處于RUNNING狀態(tài) || 線程池處于非RUNNING狀態(tài)但是任務(wù)移除失敗
else if (workerCountOf(recheck) == 0)
// 這行代碼是為了SHUTDOWN狀態(tài)下沒有活動(dòng)線程了巾表,但是隊(duì)列里還有任務(wù)沒執(zhí)行這種特殊情況汁掠。
// 添加一個(gè)null任務(wù)是因?yàn)镾HUTDOWN狀態(tài)下,線程池不再接受新任務(wù)
addWorker(null, false);
// 兩種情況:
// 1.非RUNNING狀態(tài)拒絕新的任務(wù)
// 2.隊(duì)列滿了啟動(dòng)新的線程失敿摇(workCount > maximumPoolSize)
} else if (!addWorker(command, false))
reject(command);
}
addWorker(null, false);這一行考阱,這要結(jié)合addWorker一起來看。 主要目的是防止HUTDOWN狀態(tài)下沒有活動(dòng)線程了鞠苟,但是隊(duì)列里還有任務(wù)沒執(zhí)行這種特殊情況乞榨。
4.addWorker
private boolean addWorker(Runnable firstTask, boolean core) {
retry: for (;;) {
int c = ctl.get();
int rs = runStateOf(c);// 當(dāng)前線程池狀態(tài)
// Check if queue empty only if necessary.
// 這條語句等價(jià):rs >= SHUTDOWN && (rs != SHUTDOWN || firstTask != null ||
// workQueue.isEmpty())
// 滿足下列調(diào)價(jià)則直接返回false,線程創(chuàng)建失敗:
// rs > SHUTDOWN:STOP || TIDYING || TERMINATED 此時(shí)不再接受新的任務(wù)当娱,且所有任務(wù)執(zhí)行結(jié)束
// rs = SHUTDOWN:firtTask != null 此時(shí)不再接受任務(wù)吃既,但是仍然會(huì)執(zhí)行隊(duì)列中的任務(wù)
// rs = SHUTDOWN:firtTask == null見execute方法的addWorker(null,
// false),任務(wù)為null && 隊(duì)列為空
// 最后一種情況也就是說SHUTDONW狀態(tài)下趾访,如果隊(duì)列不為空還得接著往下執(zhí)行态秧,為什么?add一個(gè)null任務(wù)目的到底是什么扼鞋?
// 看execute方法只有workCount==0的時(shí)候firstTask才會(huì)為null結(jié)合這里的條件就是線程池SHUTDOWN了不再接受新任務(wù)
// 但是此時(shí)隊(duì)列不為空申鱼,那么還得創(chuàng)建線程把任務(wù)給執(zhí)行完才行。
if (rs >= SHUTDOWN && !(rs == SHUTDOWN && firstTask == null && !workQueue.isEmpty()))
return false;
// 走到這的情形:
// 1.線程池狀態(tài)為RUNNING
// 2.SHUTDOWN狀態(tài)云头,但隊(duì)列中還有任務(wù)需要執(zhí)行
for (;;) {
int wc = workerCountOf(c);
if (wc >= CAPACITY || wc >= (core ? corePoolSize : maximumPoolSize))
return false;
if (compareAndIncrementWorkerCount(c))// 原子操作遞增workCount
break retry;// 操作成功跳出的重試的循環(huán)
c = ctl.get(); // Re-read ctl
if (runStateOf(c) != rs)// 如果線程池的狀態(tài)發(fā)生變化則重試
continue retry;
// else CAS failed due to workerCount change; retry inner loop
}
}
// wokerCount遞增成功
boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try {
final ReentrantLock mainLock = this.mainLock;
w = new Worker(firstTask);
final Thread t = w.thread;
if (t != null) {
// 并發(fā)的訪問線程池workers對(duì)象必須加鎖
mainLock.lock();
try {
// Recheck while holding lock.
// Back out on ThreadFactory failure or if
// shut down before lock acquired.
int c = ctl.get();
int rs = runStateOf(c);
// RUNNING狀態(tài) || SHUTDONW狀態(tài)下清理隊(duì)列中剩余的任務(wù)
if (rs < SHUTDOWN || (rs == SHUTDOWN && firstTask == null)) {
if (t.isAlive()) // precheck that t is startable
throw new IllegalThreadStateException();
// 將新啟動(dòng)的線程添加到線程池中
workers.add(w);
// 更新largestPoolSize
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
// 啟動(dòng)新添加的線程捐友,這個(gè)線程首先執(zhí)行firstTask,然后不停的從隊(duì)列中取任務(wù)執(zhí)行
// 當(dāng)?shù)却齥eepAlieTime還沒有任務(wù)執(zhí)行則該線程結(jié)束溃槐。見runWoker和getTask方法的代碼匣砖。
if (workerAdded) {
t.start();// 最終執(zhí)行的是ThreadPoolExecutor的runWoker方法
workerStarted = true;
}
}
} finally {
// 線程啟動(dòng)失敗,則從wokers中移除w并遞減wokerCount
if (!workerStarted)
// 遞減wokerCount會(huì)觸發(fā)tryTerminate方法
addWorkerFailed(w);
}
return workerStarted;
}
5.runWorker方法
任務(wù)添加成功后實(shí)際執(zhí)行的是runWorker這個(gè)方法昏滴,這個(gè)方法非常重要猴鲫,簡(jiǎn)單來說它做的就是:
第一次啟動(dòng)會(huì)執(zhí)行初始化傳進(jìn)來的任務(wù)firstTask;
然后會(huì)從workQueue中取任務(wù)執(zhí)行谣殊,如果隊(duì)列為空則等待keepAliveTime這么長(zhǎng)時(shí)間拂共。
final void runWorker(Worker w) {
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
// Worker的構(gòu)造函數(shù)中抑制了線程中斷setState(-1)----AQS中設(shè)置了state為-1,unlock會(huì)把state重新置為0,所以這里需要unlock從而允許中斷
w.unlock();
// 用于標(biāo)識(shí)是否異常終止姻几,finally中processWorkerExit的方法會(huì)有不同邏輯
// 為true的情況:1.執(zhí)行任務(wù)拋出異常宜狐;2.被中斷势告。
boolean completedAbruptly = true;
try {
// 如果getTask返回null那么getTask中會(huì)將workerCount遞減,如果異常了這個(gè)遞減操作會(huì)在processWorkerExit中處理
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 {
// 任務(wù)執(zhí)行前可以插入一些處理抚恒,子類重載該方法
beforeExecute(wt, task);
Throwable thrown = null;
try {
task.run();// 執(zhí)行用戶任務(wù)
} catch (RuntimeException x) {
thrown = x;
throw x;
} catch (Error x) {
thrown = x;
throw x;
} catch (Throwable x) {
thrown = x;
throw new Error(x);
} finally {
// 和beforeExecute一樣咱台,留給子類去重載
afterExecute(task, thrown);
}
} finally {
task = null;
w.completedTasks++;
w.unlock();
}
}
completedAbruptly = false;
} finally {
// 結(jié)束線程的一些清理工作
processWorkerExit(w, completedAbruptly);
}
}
從上面的源碼上可以看出,這里叉入了兩個(gè)鉤子俭驮,執(zhí)行前后處理回溺,所以可以自己擴(kuò)展ThreadPoolExecutor實(shí)現(xiàn)一些增強(qiáng)功能,如暫停執(zhí)行(jdk8源碼注釋上就有這個(gè)例子):
class PausableThreadPoolExecutor extends ThreadPoolExecutor {
private boolean isPaused;
private ReentrantLock pauseLock = new ReentrantLock();
private Condition unpaused = pauseLock.newCondition();
public PausableThreadPoolExecutor(...) { super(...); }
protected void beforeExecute(Thread t, Runnable r) {
super.beforeExecute(t, r);
pauseLock.lock();
try {
while (isPaused) unpaused.await();
} catch (InterruptedException ie) {
t.interrupt();
} finally {
pauseLock.unlock();
}
}
public void pause() {
pauseLock.lock();
try {
isPaused = true;
} finally {
pauseLock.unlock();
}
}
public void resume() {
pauseLock.lock();
try {
isPaused = false;
unpaused.signalAll();
} finally {
pauseLock.unlock();
}
}
}}
6.getTask方法(這里實(shí)現(xiàn)了一只獲取不到任務(wù)表鳍,超時(shí)就終結(jié)掉線程)
private Runnable getTask() {
boolean timedOut = false; // Did the last poll() time out?
retry: for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
// Check if queue empty only if necessary.
// 1.rs > SHUTDOWN 所以rs至少等于STOP,這時(shí)不再處理隊(duì)列中的任務(wù)
// 2.rs = SHUTDOWN 所以rs>=STOP肯定不成立馅而,這時(shí)還需要處理隊(duì)列中的任務(wù)除非隊(duì)列為空
// 這兩種情況都會(huì)返回null讓runWoker退出while循環(huán)也就是當(dāng)前線程結(jié)束了,所以必須要decrement
// wokerCount
if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
// 遞減workerCount值
decrementWorkerCount();
return null;
}
// 標(biāo)記從隊(duì)列中取任務(wù)時(shí)是否設(shè)置超時(shí)時(shí)間
boolean timed; // Are workers subject to culling?
// 1.RUNING狀態(tài)
// 2.SHUTDOWN狀態(tài)譬圣,但隊(duì)列中還有任務(wù)需要執(zhí)行
for (;;) {
int wc = workerCountOf(c);
// 1.core thread允許被超時(shí)瓮恭,那么超過corePoolSize的的線程必定有超時(shí)
// 2.allowCoreThreadTimeOut == false && wc >
// corePoolSize時(shí),一般都是這種情況厘熟,core thread即使空閑也不會(huì)被回收屯蹦,只要超過的線程才會(huì)
timed = allowCoreThreadTimeOut || wc > corePoolSize;
// 從addWorker可以看到一般wc不會(huì)大于maximumPoolSize,所以更關(guān)心后面半句的情形:
// 1. timedOut == false 第一次執(zhí)行循環(huán)绳姨, 從隊(duì)列中取出任務(wù)不為null方法返回 或者
// poll出異常了重試
// 2.timeOut == true && timed ==
// false:看后面的代碼workerQueue.poll超時(shí)時(shí)timeOut才為true登澜,
// 并且timed要為false,這兩個(gè)條件相悖不可能同時(shí)成立(既然有超時(shí)那么timed肯定為true)
// 所以超時(shí)不會(huì)繼續(xù)執(zhí)行而是return null結(jié)束線程飘庄。(重點(diǎn):線程是如何超時(shí)的脑蠕??跪削?)
if (wc <= maximumPoolSize && !(timedOut && timed))
break;
// workerCount遞減谴仙,結(jié)束當(dāng)前thread
if (compareAndDecrementWorkerCount(c))
return null;
c = ctl.get(); // Re-read ctl
// 需要重新檢查線程池狀態(tài),因?yàn)樯鲜霾僮鬟^程中線程池可能被SHUTDOWN
if (runStateOf(c) != rs)
continue retry;
// else CAS failed due to workerCount change; retry inner loop
}
// ============== 以上這一坨都是生命周期判斷以及cas遞減workcount碾盐。
try {
// 1.以指定的超時(shí)時(shí)間從隊(duì)列中取任務(wù)
// 2.core thread沒有超時(shí)
Runnable r = timed ? workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) : workQueue.take();
if (r != null)
return r;
timedOut = true;// 超時(shí)
} catch (InterruptedException retry) {
timedOut = false;// 線程被中斷重試
}
}
}
7.processWorkerExit
private void processWorkerExit(Worker w, boolean completedAbruptly) {
// 正常的話再runWorker的getTask方法workerCount已經(jīng)被減一了
if (completedAbruptly)
decrementWorkerCount();
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
// 累加線程的completedTasks
completedTaskCount += w.completedTasks;
// 從線程池中移除超時(shí)或者出現(xiàn)異常的線程
workers.remove(w);
} finally {
mainLock.unlock();
}
// 嘗試停止線程池
tryTerminate();
int c = ctl.get();
// runState為RUNNING或SHUTDOWN
if (runStateLessThan(c, STOP)) {
// 線程不是異常結(jié)束
if (!completedAbruptly) {
// 線程池最小空閑數(shù)晃跺,允許core thread超時(shí)就是0,否則就是corePoolSize
int min = allowCoreThreadTimeOut ? 0 : corePoolSize;
// 如果min == 0但是隊(duì)列不為空要保證有1個(gè)線程來執(zhí)行隊(duì)列中的任務(wù)
if (min == 0 && !workQueue.isEmpty())
min = 1;
// 線程池還不為空那就不用擔(dān)心了
if (workerCountOf(c) >= min)
return; // replacement not needed
}
// 1.線程異常退出
// 2.線程池為空毫玖,但是隊(duì)列中還有任務(wù)沒執(zhí)行掀虎,看addWoker方法對(duì)這種情況的處理
addWorker(null, false);
}
}
8.tryTerminate
每個(gè)worker退出時(shí),都會(huì)嘗試終止線程池付枫。
final void tryTerminate() {
for (;;) {
int c = ctl.get();
// 以下狀態(tài)直接返回:
// 1.線程池還處于RUNNING狀態(tài)
// 2.SHUTDOWN狀態(tài)但是任務(wù)隊(duì)列非空
// 3.runState >= TIDYING 線程池已經(jīng)停止了或在停止了
if (isRunning(c) || runStateAtLeast(c, TIDYING) || (runStateOf(c) == SHUTDOWN && !workQueue.isEmpty()))
return;
// 只能是以下情形會(huì)繼續(xù)下面的邏輯:結(jié)束線程池烹玉。
// 1.SHUTDOWN狀態(tài),這時(shí)不再接受新任務(wù)而且任務(wù)隊(duì)列也空了
// 2.STOP狀態(tài)阐滩,當(dāng)調(diào)用了shutdownNow方法
// workerCount不為0則還不能停止線程池,而且這時(shí)線程都處于空閑等待的狀態(tài)
// 需要中斷讓線程“醒”過來春霍,醒過來的線程才能繼續(xù)處理shutdown的信號(hào)。
if (workerCountOf(c) != 0) { // Eligible to terminate
// runWoker方法中w.unlock就是為了可以被中斷,getTask方法也處理了中斷叶眉。
// ONLY_ONE:這里只需要中斷1個(gè)線程去處理shutdown信號(hào)就可以了址儒。
interruptIdleWorkers(ONLY_ONE);
return;
}
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
// 進(jìn)入TIDYING狀態(tài)
if (ctl.compareAndSet(c, ctlOf(TIDYING, 0))) {
try {
// 子類重載:一些資源清理工作
terminated();
} finally {
// TERMINATED狀態(tài)
ctl.set(ctlOf(TERMINATED, 0));
// 繼續(xù)awaitTermination
termination.signalAll();
}
return;
}
} finally {
mainLock.unlock();
}
// else retry on failed CAS
}
}
9.線程池的終止
- shutdown
public void shutdown() {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
// 線程池狀態(tài)設(shè)為SHUTDOWN,如果已經(jīng)至少是這個(gè)狀態(tài)那么則直接返回
advanceRunState(SHUTDOWN);
// 注意這里是中斷所有空閑的線程:runWorker中等待的線程被中斷 → 進(jìn)入processWorkerExit →
// tryTerminate方法中會(huì)保證隊(duì)列中剩余的任務(wù)得到執(zhí)行衅疙。
interruptIdleWorkers();
onShutdown(); // hook for ScheduledThreadPoolExecutor
} finally {
mainLock.unlock();
}
tryTerminate();
}
private void interruptIdleWorkers(boolean onlyOne) {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
for (Worker w : workers) {
Thread t = w.thread;
// w.tryLock能獲取到鎖莲趣,說明該線程沒有在運(yùn)行,因?yàn)閞unWorker中執(zhí)行任務(wù)會(huì)先lock饱溢,
// 因此保證了中斷的肯定是空閑的線程喧伞。
// Worker實(shí)現(xiàn)的是不可重入鎖,獲取鎖失敗就說明任務(wù)正在執(zhí)行中
if (!t.isInterrupted() && w.tryLock()) {
try {
t.interrupt();
} catch (SecurityException ignore) {
} finally {
w.unlock();
}
}
if (onlyOne)
break;
}
}
finally {
mainLock.unlock();
}
}
- shutdownnow
public List<Runnable> shutdownNow() {
List<Runnable> tasks;
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
// STOP狀態(tài):不再接受新任務(wù)且不再執(zhí)行隊(duì)列中的任務(wù)绩郎。
advanceRunState(STOP);
// 中斷所有線程
interruptWorkers();
// 返回隊(duì)列中還沒有被執(zhí)行的任務(wù)潘鲫。
tasks = drainQueue();
}
finally {
mainLock.unlock();
}
tryTerminate();
return tasks;
}
void interruptIfStarted() {
Thread t;
// 初始化時(shí)state == -1
if (getState() >= 0 && (t = thread) != null && !t.isInterrupted()) {
try {
t.interrupt();
} catch (SecurityException ignore) {
}
}
}