继承关系
public class ThreadPoolExecutor extends AbstractExecutorService {
public abstract class AbstractExecutorService implements ExecutorService {
public interface ExecutorService extends Executor {
public interface Executor {
void execute(Runnable command);
}
常用变量
- corePoolSize 核心线程数
- maximumPoolSize最大线程数 = 临时线程 + 核心线程
- workQueue 工作队列
- threadFactory 线程工厂，创建线城池的时候初始化默认的线程工厂
- handler 任务拒绝策略，初始化时默认是defaultHandler ，是AbortPolicy()
- largestPoolSize 历史线程池最大线程数量
private volatile int corePoolSize;
private volatile int maximumPoolSize;
private int largestPoolSize;
private final BlockingQueue<Runnable> workQueue;
private volatile ThreadFactory threadFactory;
private volatile RejectedExecutionHandler handler;
private static final RejectedExecutionHandler defaultHandler =
new AbortPolicy();
线程池状态
ctl记录状态，int类型的二进制前三位作为标识
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
private static final int COUNT_BITS = Integer.SIZE - 3; //32 - 3
// runState is stored in the high-order bits
private static final int RUNNING = -1 << COUNT_BITS;//111
private static final int SHUTDOWN = 0 << COUNT_BITS;///000
private static final int STOP = 1 << COUNT_BITS;//001
private static final int TIDYING = 2 << COUNT_BITS;//010
private static final int TERMINATED = 3 << COUNT_BITS;//011
private static final int CAPACITY = (1 << COUNT_BITS) - 1;//00011111 11111111 11111111 11111111
private static int ctlOf(int rs, int wc) { return rs | wc; }
private static int workerCountOf(int c) { return c & CAPACITY; }
根据 workerCountOf(int c) ,后29位用于记录线程数
private static int workerCountOf(int c) { return c & CAPACITY; }
execute方法
运行一个线程
public void execute(Runnable command) {
if (command == null)
int c = ctl.get();
if (workerCountOf(c) < corePoolSize) {//小于核心线程池的数量
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))//添加队列失败，执行拒绝策略
reject(command);
}
remove(command)
public boolean remove(Runnable task) {
boolean removed = workQueue.remove(task);
tryTerminate(); // In case SHUTDOWN and now empty
return removed;
}
addWorker(command, true)
添加一个任务并创建线程执行，如果成功启动线程，返回true
private boolean addWorker(Runnable firstTask, boolean core) {
retry://标号，break retry 会跳出循环
for (;;) {//不停尝试添加
int c = ctl.get();
int rs = runStateOf(c);
// 线程池关闭 或者 线程队列不为空，添加失败
if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty()))
return false;
for (;;) {
int wc = workerCountOf(c);
// 线程数到达上限，添加失败
if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
if (compareAndIncrementWorkerCount(c))//当前线程数加1成功，跳出循环
break retry;
c = ctl.get(); // Re-read ctl
if (runStateOf(c) != rs)//线程池状态发生改变，重新循环
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();//队列添加线程的过程需要同步
try {
// Recheck while holding lock.
// Back out on ThreadFactory failure or if
// shut down before lock acquired.
int rs = runStateOf(ctl.get());
//如何线程池正在运行，或者线程池关闭，添加的线程为null，则可以继续添加线程
if (rs < SHUTDOWN ||
(rs == SHUTDOWN && firstTask == null)) {
if (t.isAlive()) // precheck that t is startable这时候还没有启动，如果启动了就错误了
throw new IllegalThreadStateException();
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)//记录线程池的最大线程数
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
if (workerAdded) {
t.start();//运行线程
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
}
compareAndIncrementWorkerCount(c)，尝试将当前线程数增加1个
private boolean compareAndIncrementWorkerCount(int expect) {
return ctl.compareAndSet(expect, expect + 1);
}
Worker内部类
添加成功返回true
private final class Worker
extends AbstractQueuedSynchronizer
implements Runnable
{
/** 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;
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;
}
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(); }
void interruptIfStarted() {
Thread t;
if (getState() >= 0 && (t = thread) != null && !t.isInterrupted()) {
try {
t.interrupt();
} catch (SecurityException ignore) {
}
}
}
}
Work继承runable接口，重写了run方法，调用runWorker方法
runWorker(Worker w)
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) {//当前线程或者从队列中取线程
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);
}
}
getTask()
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;
}
}
}
reject(command)
- ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常。
- ThreadPoolExecutor.DiscardPolicy：也是丢弃任务，但是不抛出异常。
- ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面的任务，然后重新尝试执行任务（重复此过程）
- ThreadPoolExecutor.CallerRunsPolicy：由调用线程处理该任务
final void reject(Runnable command) {
handler.rejectedExecution(command, this);
}
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