ThreadPoolExecutor 白话概念
线程池里面有一个集合里面放的Worker对象 集合大小对应着核心线程数
1.如果工作线程数量小于核心线程数
会创建任务放进集合,之后启动Worker线程
2.工作线程数不小于核心线程数
往队列里面放任务
Worker线程启动之后
worker线程会调runWorker()方法
它会一直循环从队列里面取任务。然后调用它的Run方法取执行它。
线程池ThreadPoolExecutor分析
一、首先看ThreadPoolExecutor#execute(Runnable)提交任务方法
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);
- 判断超过核心线程数没 没超过addWorker (Worker对象也很关键)
- 创建任务或者workQuery.offer()队列里存放任务
- 判断超出限制拒绝任务
二、ThreadPoolExecutor#addWorker(Runnable firstTask, boolean core)添加工作线程方法
第1段 判断
retry:
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
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;
}
}
这段代码主要是为了判断当前线程池状态和限制数量，不正确进行重试，略过compareAndIncrementWorkerCount成功跳出最外层循环往下走。
第2段 才是这个方法的核心部分
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) {
mainLock.lock();
try {
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
if (workerAdded) {
t.start();
}
return workerStarted;
ThreadPoolExecutor里面有一个Set
三、Worker对象，本身也是一个对象
private final class Worker extends AbstractQueuedSynchronizer implements Runnable
final Thread thread;
Runnable firstTask;
volatile long completedTasks;
Worker(Runnable firstTask) {
setState(-1); // inhibit interrupts until runWorker
this.firstTask = firstTask;
this.thread = getThreadFactory().newThread(this);
}
public void run() {
runWorker(this);
}
final void runWorker(Worker w) {
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock(); // allow interrupts
boolean completedAbruptly = true;
while (task != null || (task = getTask()) != null) {
w.lock();
beforeExecute(wt, task);
task.run();
w.completedTasks++;
w.unlock();
}
}
这段代码运行一个线程 死循环 getTask()取Runnable调用他的Run()方法 其中getTask()是关键;
四、ThreadPoolExecutor#getTask() 从队列取任务方法
boolean timedOut = false; // Did the last poll() time out?
retry:
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);
Runnable r = timed ?
workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
workQueue.take();
if (r != null)
return r;
}
死循环从workQueue取Runnable任务返回
ThreadPoolExecutor ctl字段分析
static final int COUNT_BITS = Integer.SIZE - 3;
static final int CAPACITY = (1 << COUNT_BITS) - 1;
// runState is stored in the high-order bits
static final int RUNNING = -1 << COUNT_BITS;
static final int SHUTDOWN = 0 << COUNT_BITS;
static final int STOP = 1 << COUNT_BITS;
static final int TIDYING = 2 << COUNT_BITS;
static final int TERMINATED = 3 << COUNT_BITS;
static int runStateOf(int c) { return c & ~CAPACITY; }
static int workerCountOf(int c) { return c & CAPACITY; }
static int ctlOf(int rs, int wc) { return rs | wc; }
| 线程状态 | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- | 十进制数值 |
|---|---|---|---|---|---|---|---|---|---|
| RUNNING | 1110 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | -536870912 |
| SHUTDOWN | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0 |
| STOP | 0010 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 536870912 |
| TIDYING | 0100 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 1073741824 |
| TERMINATED | 0110 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 1610612736 |
| 字段 | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- | 十进制数值 |
|---|---|---|---|---|---|---|---|---|---|
| CAPACITY | 0001 | 1111 | 1111 | 1111 | 1111 | 1111 | 1111 | 1111 | 536870911 |
| ~CAPACITY | 1110 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | -536870912 |
由此二进制结果 分析
runStateOf() c & ~CAPACITY
相当于就是取前4位的值
workerCountOf() c & CAPACITY
相当就是取后面的值
ctl一个int型4个字节 4*8=32 位 里面存了两部分的值
前面4位存的是线程的5个状态,后面28位存的工作线程池的数量
int c = ctl.get();
int rs = runStateOf(c);
if (rs >= SHUTDOWN &&! (rs == SHUTDOWN &&firstTask == null &&! workQueue.isEmpty()));
这种rs >= SHUTDOWN 相当SHUTDOWN,STOP,TIDYING,TERMINATED这些字段是符合状态的。