public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler)
参数说明
| 参数 | 说明 |
|---|---|
| corePoolSize | 核心线程数，也指线程池的基本大小。当任务提交时，即时有其他空闲线程也会创建一个新线程执行任务，直到线程数等于 corePoolSize |
| maximumpoolSize | 线程池最大数量。如果队列满并且创建的线程数小于最大线程数，则会创建新的现场执行任务。对于无界队列无用 |
| keepAliveTime | 工作线程活动保持时间。当工作线程空闲后，在 keepAliveTime 内没有重新执行任务，则会被销毁 |
| unit | keepAliveTime的单位 |
| workQueue | 任务队列，用以保存等待执行的任务的阻塞队列 |
| threadFactory | 先创创建工厂 |
| handler | 饱和策略，当队列和线程池满后，说明线程池处于饱和状态。 |
-
常用的阻塞队列
- ArrayBlockingQueue
- LinkedBlockingQueue
- SynchronousQueue
- PriorityBlockingQueue
-
常用的饱和策略
- AbortPolicy
- CallerRunsPolicy
- DiscardOldestPolicy
- DiscardPolicy
常见的线程池，用线程池工具类 Executors 创建
| 线程池 | corePoolSize | maximumPoolSize | keepAliveTime | unit | workQueue | threadFactory | handler |
|---|---|---|---|---|---|---|---|
| FixedThreadPool | 自定义 | 等于 corePoolSize | 0 | MILLISECONDS | LinkedBlockingQueue | Executors$DefaultThreadFactory | AbortPolicy |
| SingleThreadExecutor | 1 | 1 | 0 | MILLISECONDS | LinkedBlockingQueue | 自定义或Executors$DefaultThreadFactory | AbortPolicy |
| CachedThreadPool | 0 | Integer.MAX_ VALUE | 60 | SECONDS | SynchronousQueue | 自定义或Executors$DefaultThreadFactory | AbortPolicy |
默认的构造函数
@Executors
public static ExecutorService newFixThreadPool(int nThreads);
public static ExecutorService newFixThreadPool(int nThreads, ThreadFactory threadFactory)
public static ExecutorService newSingleThreadExecutor();
public static ExecutorService newSingleThreadExecutor(ThreadFactory factory);
public static ExecutorService newCachedThreadPool();
public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory)
FixThread 介绍：
从参数构造可以看出来 FixThread 内的线程全都是核心线程，使用的队列是无界阻塞队列 LinkedBlockingQueue，因此 FixThread 会从无界队列中反复获取任务交由核心线程执行
SingleThreadExecutor:
其核心线程数和最大线程数被设置为 1，任务队列使用无界队列 LinkedBlockingQueue，因此该线程池会反复从 LinkedBlockingQueue 中获取任务来执行，每次执行一个
CachedThreadPool:
其核心线程数为 0，最大线程数为Integer.MAX_VALUE，并且 keepAliveTime 设置为 60 秒，使用的是没有容量的 SynchronousQueue，因此每提交一个任务，如果没有多余的线程可以使用，那么每次都会创建一个线程去执行任务。于是乎如果任务的提交速度远大于任务的执行速度，那么会因为创建过多线程而耗尽 CPU。
线程池：
无论是 FixThread 还是 SingleThreadExecutor 还是 CacherThreadPool，其内部都是ThreadPoolExecutor对象，参数介绍在上面已经说明了。当执行一个任务时，需要调用 execute(Runnable)@ThreadPoolExecutor
public void execute(Runnable command){
if(command == null){
throw new NullPointException();
}
//默认值是 e0000000
int c= ctl.get();
//从 workerCountOf(c)返回 c&1ffffffff，因此线程最大为 0x1fffffff
if(workerCountOf(c) < corePoolSize){
//当线程数小于 corePoolSize，则
if(addWorker(command, true)){
c = ctl.get();
}
}
//如果线程池是 Running 的并且任务入队成功
if(isRunning(c) && workQueue.offer(command)){
int recheck = ctl.get();
//如果线程池非 Running 并且任务出队成功，则执行拒绝策略
if(!isRunning(recheck) && remove(command)){
reject(command);
}else if(workerCountOf(recheck) == 0){
//
addWorker(null,false);
}
}else if(!addWorker(command, flase)){
reject(command);
}
}
看一些参数说明
//初始值是 e0000000,最高位表示线程池状态，低 7 位表示线程数，
//如 e 代表 RUNNING,0 代表 SHUTDOWN,2代表 STOP,4代表 TIDYING,6代表 TERMINATED
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
//29
private static final int COUNT_BITS = Integer.SIZE - 3;
//1fffffff
private static final int CAPACITY = (1 << COUNT_BITS) - 1;
// runState is stored in the high-order bits
0xe0000000
private static final int RUNNING = -1 << COUNT_BITS;
0x0
private static final int SHUTDOWN = 0 << COUNT_BITS;
0x20000000
private static final int STOP = 1 << COUNT_BITS;
0x40000000
private static final int TIDYING = 2 << COUNT_BITS;
0x6000000
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; }
private boolean addWorker(Runnable firstTask, boolean core){
retry:
for(;;){
int c= ctl.get();
int rs=runStateOf(c);
//runstateOf()是做 mask 操作，取出线程池状态
//mask是 e00000000,
//SHUTWODN是非 RUNNING状态的最小值，如果>=SHUTDOWN表示线程池非 RUNNING
if(rs >= SHUTDOWN &&
!(rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty())){
return false;
}
for(;;){
int wc = wokerCountOf(c);
//线程池当前线程数量大于线程池容量 或
//如果是用核心线程执行且大于核心线程数阈值
//或是用非核心线程执行且大于非核心线程数阈值
if(wc >= CAPACITY
|| wc>=(core? corePoolSize : maximumPoolSize)){
return false;
}
//CAS 增加线程池线程数，则否重试
if(compareAndIncrementWorkerCount(c)){
break retry;
}
//? re-check
c = ctl.get();
if(runStateOf(c) != rs){
continue retry;
}
}
}
//以下是为了增加工作线程
boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try{
//将 Runnable 封装为 Worker，内部用线程工厂类创建线程
w = new Worker(firstTask);
final Thread t = w.thread;
if(t!=null){
final RenntrantLock mainLock = this.mainLock;
//锁
mainLock.lock();
try{
int rs = runStateOf(ctl.get());
if(rs < SHUTDOWN
||(rs == SHUTDOWN && firstTask == null)){
if(t.isAlive()){
throw new IllegalThreadStateException();
}
workers.add(w);
int s = workers.size();
if(s>largestPoolSize){
largestPoolSize = s;
}
workerAdded = true;
}
}finally{
main.unlock();
}
if(workerAdded){
//开始工作
t.start();
workerStarted = true;
}
}
}finally{
if(!workStarted){
addWorkerFailed(w);
}
}
return workerStated;
}
@ThreadPoolExecutor$Worker
Worker(Runnable firstTask){
setState(-1);
this.firstTask = firstTask;
this.thread=getThreadFactory().newThread(this);
}
//当在 addWorker()中调用 Worker.thread.start()则会调用 run()@Worker
public void run(){
runWorker(this);
}
final void runWorker(Worker w){
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock();
boolean completedAbruptly = true;
try{
//循环取任务并且执行
while(task !=null || (task = getTask) !=null){
w.lock();
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(Exception x){
throw x;
}finally {
afterExecute(task, thrown);
}
}finally{
task = null
w.completedTasks++;
w.unlock;
}
}
completedAbruptly = false;
}finally{
processWorkerExit(w, completedAbruptly);
}
}
//从任务队列取出任务
private Runnable getTask(){
boolean timeOut = false;
for(;;){
int c = ctl.get();
int rs = runStateOf(c);
if(rs>= SHUTDOWN && (rs >= STOP)||workQueue.isEmpty()){
decrementWorkerCount();
return null;
}
int wc = workerCountOf(c);
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.pool(keepALiveTime, TimeUnit.NANOSECOND):
workQueue.take();
if(r !=null){
return r;
}
timeOut = true;
}catch(InterruptedException retry){
timeOut = false;
}
}
}
。。。
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