實戰java高併發程序設計第三章(一)
1. 同步控制
synchronized的擴展:重入鎖
同步控制不只有synchronized配合object.wait()以及object.notify(),也有加強版的reentrantLock(重入鎖)java
public class ReenterLock implements Runnable{
public static ReentrantLock lock=new ReentrantLock();
public static int i=0;
@Override
public void run() {
for(int j=0;j<10000000;j++){
lock.lock();
lock.lock(); //此處演示重入性
try{
i++;
}finally{
lock.unlock(); //退出臨界區必須解鎖
lock.unlock();
}
}
}
public static void main(String[] args) throws InterruptedException {
ReenterLock tl=new ReenterLock();
Thread t1=new Thread(tl);
Thread t2=new Thread(tl);
t1.start();t2.start();
t1.join();t2.join();
System.out.println(i); //計算結果爲 20000000
}
}
咱們來看下reentrantlock相比synchronized鎖有何優勢:算法
中斷響應
面對死鎖,彷佛synchronized沒有任何主動解決策略,而reentrantlock則能夠輕鬆解決緩存
public class IntLock implements Runnable {
public static ReentrantLock lock1 = new ReentrantLock();
public static ReentrantLock lock2 = new ReentrantLock();
int lock;
/**
* 控制加鎖順序，方便構造死鎖
* @param lock
*/
public IntLock(int lock) {
this.lock = lock;
}
@Override
public void run() {
try {
if (lock == 1) {
lock1.lockInterruptibly(); //可中斷的加鎖
try{
Thread.sleep(500);
}catch(InterruptedException e){}
lock2.lockInterruptibly();
} else {
lock2.lockInterruptibly();
try{
Thread.sleep(500);
}catch(InterruptedException e){}
lock1.lockInterruptibly();
}
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println(Thread.currentThread().getName()+":線程被中斷");
} finally {
if (lock1.isHeldByCurrentThread())
lock1.unlock();
if (lock2.isHeldByCurrentThread())
lock2.unlock();
System.out.println(Thread.currentThread().getName()+":線程退出");
}
}
public static void main(String[] args) throws InterruptedException {
IntLock r1 = new IntLock(1);
IntLock r2 = new IntLock(2);
Thread t1 = new Thread(r1,"線程1");
Thread t2 = new Thread(r2,"線程2");
t1.start();t2.start();
Thread.sleep(1000);
//中斷其中一個線程
t2.interrupt();
}
}
// 輸出結果:
// java.lang.InterruptedException
// at //java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireInterruptibly(AbstractQueuedSynchronizer.java:898)
// at //java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(AbstractQueuedSynchronizer.java:1222)
// at java.util.concurrent.locks.ReentrantLock.lockInterruptibly(ReentrantLock.java:335)
// at geym.conc.ch3.synctrl.IntLock.run(IntLock.java:31)
// at java.lang.Thread.run(Thread.java:745)
// 線程2:線程被中斷
// 線程2:線程退出
// 線程1:線程退出
由上可知,當t1,t2造成死鎖時,能夠主動利用中斷來解開,但完成任務的只有t1,t2被中斷. 而若是換成synchronized則將沒法進行中斷多線程
鎖申請等待時限
lock1.tryLock(); //嘗試獲取鎖,得到當即返回true,未得到當即返回false lock1.tryLock(5, TimeUnit.SECONDS); //嘗試獲取鎖,5秒內未得到則返回false,得到返回true
public class TryLock implements Runnable {
public static ReentrantLock lock1 = new ReentrantLock();
public static ReentrantLock lock2 = new ReentrantLock();
int lock;
public TryLock(int lock) {
this.lock = lock;
}
@Override
public void run() {
if (lock == 1) {
while (true) {
if (lock1.tryLock()) {
try {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
}
if (lock2.tryLock()) {
try {
System.out.println(Thread.currentThread()
.getId() + ":My Job done");
return;
} finally {
lock2.unlock();
}
}
} finally {
lock1.unlock();
}
}
}
} else {
while (true) {
if (lock2.tryLock()) {
try {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
}
if (lock1.tryLock()) {
try {
System.out.println(Thread.currentThread()
.getId() + ":My Job done");
return;
} finally {
lock1.unlock();
}
}
} finally {
lock2.unlock();
}
}
}
}
}
public static void main(String[] args) throws InterruptedException {
TryLock r1 = new TryLock(1);
TryLock r2 = new TryLock(2);
Thread t1 = new Thread(r1);
Thread t2 = new Thread(r2);
t1.start();
t2.start();
}
}
// 15:My Job done
// 14:My Job done
使用trylock能夠有效地避免產生死鎖框架
公平鎖
synchronized鎖爲非公平鎖,而reentrantLock既能夠是公平鎖也能夠是非公平鎖
非公平鎖容易產生飢餓,公平鎖先進先出,但效率不敵非公平鎖dom
public ReentrantLock(boolean fair)
重入鎖的搭檔Condition
Condition和object.wait(),object.notify()方法相似
condition的基本方法以下:ide
void await() throws InterruptedException; //使當前線程等待,釋放鎖,能響應signal和signalAll方法,響應中斷 void awaitUninterruptibly(); //相似 await,但不響應中斷 long awaitNanos(long nanosTimeout)throws InterruptedException; //等待一段時間 boolean await (long time,TimeUnit unit)throws InterruptedException; boolean awaitUntil(Date deadline)throws InterruptedException; void signal()； //喚醒一個等待中的線程 void signalAll(); //喚醒全部等待中的線程
JDK內部就有不少對於ReentrantLock的使用,如ArrayBlockingQueue函數
//在 ArrayBlockingQueue中的一些定義
boolean fair = true;
private final ReentrantLock lock = new ReentrantLock(fair);
private final Condition notEmpty = lock.newCondition();
private final Condition notFull = lock.newCondition();
//put(方法的實現
public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lockInterruptibly(); //put方法作同步
try {
try {
while (count == items.length) //隊列已滿
notFull.await(); //等待隊列有足夠的空間
} catch (InterruptedException ie) {
notFull.signal();
throw ie;
}
insert(e); //notFull被通知時,說明有足夠的空間
} finally {
lock.unlock();
}
}
private void insert(E x) {
items[putIndex] = x;
putIndex = inc(putIndex);
++count;
notFull.signal(); //通知take方法的線程,隊列已有數據
}
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly(); //對take()方法作同步
try {
try {
while (count == 0) //若是隊列爲空
notEmpty.await(); //則消費者隊列要等待一個非空的信號
} catch (InterruptedException ie) {
notEmpty.signal();
throw ie;
}
E x = extract();
return x;
} finally {
lock.unlock();
}
}
private E extract() {
final E[] items = this.items;
E x = items[takeIndex];
items[takeIndex] = null;
takeIndex = inc(takeIndex);
--count;
notFull.signal(); //通知put線程隊列已有空閒空間
return x;
}
多線程同時訪問:信號量(semaphore)
同步鎖只能容許一個線程進行訪問,信號量能夠指定多個線程同時訪問同一個資源.工具
//構造方法
public Semaphore(int permits) //傳入int表示能同時訪問的線程數
public Semaphore(int permits, boolean fair) //線程數,是否公平鎖
//實例方法
public void acquire() throws InterruptedException //獲取一個訪問權限,會阻塞線程,會被打斷
public void acquireUninterruptibly() //獲取一個訪問權限,會阻塞線程,不會被打斷
public boolean tryAcquire() //獲取一個訪問權限,當即返回
public boolean tryAcquire(long timeout, TimeUnit unit) //獲取一個訪問權限,嘗試一段時間
public void release() //釋放一個訪問權限
public class SemapDemo implements Runnable {
final Semaphore semp = new Semaphore(5);
@Override
public void run() {
try {
semp.acquire();
Thread.sleep(2000);
System.out.println(Thread.currentThread().getId() + ":done!");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
semp.release(); //使用完後要釋放,不然會引發信號量泄漏
}
}
public static void main(String[] args) {
ExecutorService exec = Executors.newFixedThreadPool(20);
final SemapDemo demo = new SemapDemo();
for (int i = 0; i < 20; i++) {
exec.submit(demo);
}
}
}
//輸出結果
//每次輸出5個結果,對應信號量的5個許可
讀寫鎖ReadWriteLock
讀寫鎖適用於讀多寫少的場景,讀讀之間爲並行,讀寫之間爲串行,寫寫之間也爲串行
public class ReadWriteLockDemo {
private static Lock lock=new ReentrantLock();
private static ReentrantReadWriteLock readWriteLock=new ReentrantReadWriteLock(); //獲取讀寫鎖
private static Lock readLock = readWriteLock.readLock(); //讀鎖
private static Lock writeLock = readWriteLock.writeLock(); //寫鎖
private int value;
public Object handleRead(Lock lock) throws InterruptedException{
try{
lock.lock(); //模擬讀操做
Thread.sleep(1000); //讀操做的耗時越多，讀寫鎖的優點就越明顯
return value;
}finally{
lock.unlock();
}
}
public void handleWrite(Lock lock,int index) throws InterruptedException{
try{
lock.lock(); //模擬寫操做
Thread.sleep(1000);
value=index;
}finally{
lock.unlock();
}
}
public static void main(String[] args) {
final ReadWriteLockDemo demo=new ReadWriteLockDemo();
Runnable readRunnale=new Runnable() {
@Override
public void run() {
try {
demo.handleRead(readLock);
// demo.handleRead(lock);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Runnable writeRunnale=new Runnable() {
@Override
public void run() {
try {
demo.handleWrite(writeLock,new Random().nextInt());
// demo.handleWrite(lock,new Random().nextInt());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
for(int i=0;i<18;i++){
new Thread(readRunnale).start();
}
for(int i=18;i<20;i++){
new Thread(writeRunnale).start();
}
}
}
//結果:
//讀寫鎖明顯要比單純的鎖要更快結束,說明讀寫鎖確實提高很多效率
倒計數器CountDownLatch
讓一個線程等待,知道倒計時結束
public class CountDownLatchDemo implements Runnable {
static final CountDownLatch end = new CountDownLatch(10); //構造倒計時器,倒計數爲10
static final CountDownLatchDemo demo=new CountDownLatchDemo();
@Override
public void run() {
try {
//模擬檢查任務
Thread.sleep(new Random().nextInt(10)*1000);
System.out.println("check complete");
end.countDown(); //倒計時器減1
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws InterruptedException {
ExecutorService exec = Executors.newFixedThreadPool(10);
for(int i=0;i<10;i++){
exec.submit(demo);
}
//等待檢查
end.await(); //主線程阻塞,待其餘線程所有完成後再喚醒主線程
//發射火箭
System.out.println("Fire!");
exec.shutdown();
}
}
循環柵欄CyclicBarrier
循環柵欄相似於倒計時器,可是計數器能夠反覆使用,cyclicBarrier比CountDownLatch稍微強大些,能夠傳入一個barrierAction,barrierAction指每次完成計數便出發一次
public CyclicBarrier(int parties,Runnable barrierAction) //構造方法
public class CyclicBarrierDemo {
public static class Soldier implements Runnable {
private String soldier;
private final CyclicBarrier cyclic;
Soldier(CyclicBarrier cyclic, String soldierName) {
this.cyclic = cyclic;
this.soldier = soldierName;
}
public void run() {
try {
//等待全部士兵到齊
cyclic.await(); //觸發一次循環柵欄,達到計數器後纔會進行下一步工做
doWork();
//等待全部士兵完成工做
cyclic.await(); //再次觸發循環柵欄,達到計數器後纔會進行下一步工做
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}
void doWork() {
try {
Thread.sleep(Math.abs(new Random().nextInt()%10000)); //模擬工做
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(soldier + ":任務完成");
}
}
public static class BarrierRun implements Runnable { //用於傳入CyclicBarrier的構造方法,做爲達到計數器數值後的觸發任務, 能夠被屢次調用
boolean flag;
int N;
public BarrierRun(boolean flag, int N) {
this.flag = flag;
this.N = N;
}
public void run() {
if (flag) {
System.out.println("司令:[士兵" + N + "個，任務完成！]");
} else {
System.out.println("司令:[士兵" + N + "個，集合完畢！]");
flag = true;
}
}
}
public static void main(String args[]) throws InterruptedException {
final int N = 10;
Thread[] allSoldier=new Thread[N];
boolean flag = false;
CyclicBarrier cyclic = new CyclicBarrier(N, new BarrierRun(flag, N));
//設置屏障點，主要是爲了執行這個方法
System.out.println("集合隊伍！");
for (int i = 0; i < N; ++i) {
System.out.println("士兵 "+i+" 報道！");
allSoldier[i]=new Thread(new Soldier(cyclic, "士兵 " + i));
allSoldier[i].start();
}
}
}
注意: 一旦其中一個被interrupt後,極可能會拋出一個interruptExpection和9個BrokenBarrierException,表示該循環柵欄已破損,防止其餘線程進行無所謂的長久等待
線程阻塞工具LockSupport
LockSupport是一個很是實用的線程阻塞工具,不須要獲取某個對象的鎖(如wait),也不會拋出interruptedException異常
public static void park() //掛起當前線程, public static void park(Object blocker) //掛起當前線程,顯示阻塞對象,parking to wait for <地址值>
public class LockSupportDemo {
public static Object u = new Object();
static ChangeObjectThread t1 = new ChangeObjectThread("t1");
static ChangeObjectThread t2 = new ChangeObjectThread("t2");
public static class ChangeObjectThread extends Thread {
public ChangeObjectThread(String name){
super.setName(name);
}
@Override
public void run() {
synchronized (u) {
System.out.println("in "+getName());
LockSupport.park(this);
}
}
}
public static void main(String[] args) throws InterruptedException {
t1.start();
Thread.sleep(100);
t2.start();
LockSupport.unpark(t1);
LockSupport.unpark(t2); //即便unpark發生在park前,也可使程序正常結束
t1.join();
t2.join();
}
}
LockSupport使用了相似信號量的機制,它爲每一個線程準備一個許可,若是許可可用,park當即返回,而且消費這個許可(轉爲不可用),若是許可不可用,就會阻塞,而unpark方法就是使一個許可變爲可用 locksupport.park()能夠相應中斷,可是不會拋出interruptedException,咱們能夠用Thread.interrupted等方法中獲取中斷標記.
public class LockSupportIntDemo {
public static Object u = new Object();
static ChangeObjectThread t1 = new ChangeObjectThread("t1");
static ChangeObjectThread t2 = new ChangeObjectThread("t2");
public static class ChangeObjectThread extends Thread {
public ChangeObjectThread(String name){
super.setName(name);
}
@Override
public void run() {
synchronized (u) {
System.out.println("in "+getName());
LockSupport.park();
if(Thread.interrupted()){ //檢測到中斷位,並清除中斷狀態
System.out.println(getName()+" 被中斷了");
}
if (Thread.currentThread().isInterrupted()){ //中斷狀態已被清除,沒法檢測到
System.out.println(1);
}
}
System.out.println(getName()+"執行結束");
}
}
public static void main(String[] args) throws InterruptedException {
t1.start();
Thread.sleep(100);
t2.start();
t1.interrupt();
LockSupport.unpark(t2);
}
}
//輸出:
//in t1
//t1 被中斷了
//t1執行結束
//in t2
//t2執行結束
Guava和Limiter限流
限流算法通常有兩種:漏桶算法和令牌桶算法 漏桶算法: 利用緩存區,全部請求進入系統,都在緩存區中保存,而後以固定的流速流出緩存區進行處理. 令牌桶算法: 桶中存放令牌,每一個請求拿到令牌後才能進行處理,若是沒有令牌,請求要麼等待,要麼丟棄.RateLimiter就是採用這種算法
public class RateLimiterDemo {
static RateLimiter limiter = RateLimiter.create(2); //每秒處理2個請求
public static class Task implements Runnable {
@Override
public void run() {
System.out.println(System.currentTimeMillis());
}
}
public static void main(String args[]) throws InterruptedException {
for (int i = 0; i < 50; i++) {
limiter.acquire(); //過剩流量會等待
new Thread(new Task()).start();
}
}
}
// 某些場景傾向於丟棄過剩流量,tryAcquire則是當即返回,不會阻塞
// for (int i = 0; i < 50; i++) {
// if(!limiter.tryAcquire()) {
// continue;
// }
// new Thread(new Task()).start();
// }
2. 線程池
Executors框架
Executor框架提供了各類類型的線程池,主要有如下工廠方法:性能
//固定線程數量,當有新任務提交時,若池中有空閒線程則當即執行,若沒有空閒線程,任務會被暫存在一個任務隊列中,直到有空閒線程 public static ExecutorService newFixedThreadPool(int nThreads) //返回只有一個線程的線程池,多餘任務被保存到一個任務隊列中,線程空閒時,按先入先出的順序執行隊列中的任務 public static ExecutorService newSingleThreadPoolExecutor() //線程數量不固定,優先使用空閒線程,多餘任務會建立新線程 public static ExecutorService newCachedThreadPool() //線程數量爲1,給定時間執行某任務,或週期性執行任務 public static ScheduledExecutorService newSingleThreadScheduledExecutor() //線程數量能夠指定,定時或週期性執行任務 public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize)
計劃任務:newScheduledThreadPool主要方法
//給定時間,對任務進行一次調度
public ScheduledFuture<?> schedule(Runnable command,long delay, TimeUnit unit);
//週期調度,以任務完成後間隔固定時間調度下一個任務,(二者相加)
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,long initialDelay,
long delay,
TimeUnit unit);
//週期調度,兩個任務開始的時間差爲固定間隔,若是任務時間大於間隔時間則以任務時間爲準(二者取其大者)
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,long initialDelay,
long period,
TimeUnit unit);
注意: 任務異常時後續全部任務都將中止調度,所以必須保證全部任務異常均被正常處理.
- 核心線程池 ThreadPoolExecutor
ThreadPoolExecutor構造函數:
public ThreadPoolExecutor(int corePoolSize, //核心線程池大小
int maximumPoolSize, //最大線程池大小
long keepAliveTime, //線程池中超過corePoolSize數目的空閒線程最大存活時間；能夠allowCoreThreadTimeOut(true)使得核心線程有效時間
TimeUnit unit, //keepAliveTime時間單位
BlockingQueue<Runnable> workQueue, //阻塞任務隊列
ThreadFactory threadFactory, //新建線程工廠
RejectedExecutionHandler handler ) //當提交任務數超過maxmumPoolSize+workQueue之和時，任務會交給RejectedExecutionHandler來處理
workQueue指被提交可是未執行的任務隊列,是BlockingQueue接口的對象
1.直接提交隊列:SynchronousQueue,該隊列沒有容量,每一個插入操做對應一個刪除操做,即提交的任務老是會交給線程執行,若是沒有空閒進程,則建立新線程,數量達最大則執行拒絕策略,通常須要設置很大的maximumPoolSize
2.有界任務隊列:ArrayBlockingQueue,有新任務時,若線程池的實際線程數小於corePoolSize,優先建立新線程,若大於corePoolSize,加入到等待隊列,若隊列已滿,不大於maximumPoolSize前提下,建立新線程執行;當且僅當等待隊列滿時纔會建立新線程,不然數量一直維持在corePoolSize
3.無界任務隊列:LinkedBlockingQueue,小於corePoolSize時建立線程,達到corePoolSize則加入隊列直到資源消耗殆盡
4.優先任務隊列:PriorityBlockingQueue,特殊無界隊列,老是保證高優先級的任務先執行.
Executors分析
newFixedThreadPool: corePoolSize=maximumPoolSize,線程不會超過corePoolSize,使用LinkedBlockingQueue newSingleThreadPoolExecutor: newFixedThreadPool的弱化版,corePoolSize只有1 newCachedThreadPool: corePoolSize=0,maximumPoolSize爲無窮大,空閒線程60秒回收,使用SynchronousQueue隊列
ThreadPoolExecutor的execute()方法執行邏輯
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) { //檢查是否小於corePoolSize
if (addWorker(command, true)) //添加線程,執行任務
return;
c = ctl.get();
}
if (isRunning(c) && workQueue.offer(command)) { //添加進隊列
int recheck = ctl.get();
if (! isRunning(recheck) && remove(command)) //雙重校驗
reject(command);
else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}
else if (!addWorker(command, false)) //提交線程池失敗
reject(command); //拒絕執行
}
拒絕策略
**AbortPolicy**:該策略會直接拋出異常,阻止系統正常工做。 **CallerRunsPolicy**:只要線程池未關閉,該策略直接在調用者線程中,運行當前被丟棄的任務。顯然這樣作不會真的丟棄任務,可是,任務提交線程的性能極有可 能會急劇降低。 任務,並嘗試再次提交當前任務。 **DiscardOldestPolicy**:該策略將丟棄最老的一個請求,也就是即將被執行的一個 **DiscardPolicy**:該策略默默地丟棄沒法處理的任務,不予任何處理。若是容許任務丟失,我以爲這多是最好的一種方案了吧!
自定義ThreadFactory
public static void main(String[] args) throws InterruptedException {
MyTask task = new MyTask();
ExecutorService es = new ThreadPoolExecutor(5, 5,
0L, TimeUnit.MILLISECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactory(){
@Override
public Thread newThread(Runnable r) { //自定義建立線程的方法
Thread t= new Thread(r);
t.setDaemon(true);
System.out.println("create "+t);
return t;
}
}
);
for (int i = 0; i < 5; i++) {
es.submit(task);
}
Thread.sleep(2000);
}
擴展線程池
public class ExtThreadPool {
public static class MyTask implements Runnable {
public String name;
public MyTask(String name) {
this.name = name;
}
@Override
public void run() {
System.out.println("正在執行" + ":Thread ID:" + Thread.currentThread().getId()
+ ",Task Name=" + name);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) throws InterruptedException {
ExecutorService es = new ThreadPoolExecutor(5, 5, 0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()) {
@Override
protected void beforeExecute(Thread t, Runnable r) {
System.out.println("準備執行：" + ((MyTask) r).name);
}
@Override
protected void afterExecute(Runnable r, Throwable t) {
System.out.println("執行完成：" + ((MyTask) r).name);
}
@Override
protected void terminated() {
System.out.println("線程池退出");
}
};
for (int i = 0; i < 5; i++) {
MyTask task = new MyTask("TASK-GEYM-" + i);
es.execute(task);
Thread.sleep(10);
}
es.shutdown(); //等待全部任務執行完畢後再關閉
}
}
異常堆棧消息
線程池中的異常堆棧可能不會拋出,須要咱們本身去包裝
public class TraceThreadPoolExecutor extends ThreadPoolExecutor {
public TraceThreadPoolExecutor(int corePoolSize, int maximumPoolSize,
long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
@Override
public void execute(Runnable task) {
super.execute(wrap(task, clientTrace(), Thread.currentThread()
.getName()));
}
@Override
public Future<?> submit(Runnable task) {
return super.submit(wrap(task, clientTrace(), Thread.currentThread()
.getName()));
}
private Exception clientTrace() {
return new Exception("Client stack trace");
}
private Runnable wrap(final Runnable task, final Exception clientStack,
String clientThreadName) {
return new Runnable() {
@Override
public void run() {
try {
task.run(); //外層包裹trycatch,便可打印出異常
} catch (Exception e) {
clientStack.printStackTrace();
throw e;
}
}
};
}
}
Fork/Join框架
相似於mapreduce,用於大數據量,fork()創造子線程,join表示等待,
public class CountTask extends RecursiveTask<Long>{
private static final int THRESHOLD = 10000; //任務分解規模
private long start;
private long end;
public CountTask(long start,long end){
this.start=start;
this.end=end;
}
@Override
public Long compute(){
long sum=0;
boolean canCompute = (end-start)<THRESHOLD; //表示計算極限10000,超出此值須要使用forkjoin
if(canCompute){
for(long i=start;i<=end;i++){
sum +=i;
}
}else{
//分紅100個小任務
long step=(start+end)/100;
ArrayList<CountTask> subTasks=new ArrayList<CountTask>();
long pos=start;
for(int i=0;i<100;i++){
long lastOne=pos+step;
if(lastOne>end)lastOne=end; //最後一個任務可能小於step,故須要此步
CountTask subTask=new CountTask(pos,lastOne); //子任務
pos+=step+1; //調整下一個任務
subTasks.add(subTask);
subTask.fork(); //fork子任務
}
for(CountTask t:subTasks){
sum+=t.join(); //聚合任務
}
}
return sum;
}
public static void main(String[]args){
ForkJoinPool forkJoinPool = new ForkJoinPool();
CountTask task = new CountTask(0,200000000000L);
ForkJoinTask<Long> result = forkJoinPool.submit(task);
try{
long res = result.get();
System.out.println("sum="+res);
}catch(InterruptedException e){
e.printStackTrace();
}catch(ExecutionException e){
e.printStackTrace();
}
}
}
注意: 若是任務的劃分層次不少,一直得不到返回,可能有兩種緣由: 1.系統內線程數量越積越多,致使性能嚴重降低 2.函數調用層次變多,致使棧溢出
Guava對線程池的拓展
1.特殊的DirectExecutor線程池
Executor executor=MoreExecutors.directExecutor(); // 僅在當前線程運行,用於抽象
2.Daemon線程池
提供將普通線程轉換爲Daemon線程.不少狀況下,咱們不但願後臺線程池阻止程序的退出
public class MoreExecutorsDemo2 {
public static void main(String[] args) {
ThreadPoolExecutor exceutor = (ThreadPoolExecutor)Executors.newFixedThreadPool(2);
MoreExecutors.getExitingExecutorService(exceutor);
exceutor.execute(() -> System.out.println("I am running in " + Thread.currentThread().getName()));
}
}
3.future模式擴展待續....
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