线程池参数动态调整

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线程池的参数动态调整

总结：
线程池类 ThreadPoolExecutor 中已经提供了对应的方法，允许动态修改线程池参数：
1、动态修改核心数
当 allowCoreThreadTimeOut 参数设置为 true 的时候，
核心线程在空闲了 keepAliveTime 的时间后也会被回收的，
相当于线程池自动给你动态修改了
public void setCorePoolSize(int corePoolSize) { 

if (corePoolSize < 0)
throw new IllegalArgumentException();
int delta = corePoolSize - this.corePoolSize;
this.corePoolSize = corePoolSize;
if (workerCountOf(ctl.get()) > corePoolSize)
interruptIdleWorkers();
else if (delta > 0) { 

int k = Math.min(delta, workQueue.size());
while (k-- > 0 && addWorker(null, true)) { 

if (workQueue.isEmpty())
break;
}
}
}
2、动态修改最大线程数
public void setMaximumPoolSize(int maximumPoolSize) { 

if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize)
throw new IllegalArgumentException();
this.maximumPoolSize = maximumPoolSize;
if (workerCountOf(ctl.get()) > maximumPoolSize)
interruptIdleWorkers();
}
3、动态修改存活时间
public void setKeepAliveTime(long time, TimeUnit unit) { 

if (time < 0)
throw new IllegalArgumentException();
if (time == 0 && allowsCoreThreadTimeOut())
throw new IllegalArgumentException("Core threads must have nonzero keep alive times");
long keepAliveTime = unit.toNanos(time);
long delta = keepAliveTime - this.keepAliveTime;
this.keepAliveTime = keepAliveTime;
if (delta < 0)
interruptIdleWorkers();
}
4、动态修改线程工厂
public void setThreadFactory(ThreadFactory threadFactory) { 

if (threadFactory == null)
throw new NullPointerException();
this.threadFactory = threadFactory;
}
5、动态修改拒绝策略
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { 

if (handler == null)
throw new NullPointerException();
this.handler = handler;
}
6、可以发现是没有提供方法修改线程队列的，这是因为线程队列的 capacity 参数被 final 所修饰了
private final int capacity;
但是我们可以自定义线程队列，然后把 capacity 参数去掉 final 修饰即可。
操作起来也非常方便，把 LinkedBlockingQueue 粘贴一份出来，修改个名字，
然后把 capacity 参数的 final 修饰符去掉，并提供其对应的 get/set 方法
private volatile int capacity;
public int getCapacity() { 

return capacity;
}
public void setCapacity(int capacity) { 

this.capacity = capacity;
}