我遇到了Java 6的ThreadPoolExecutor一個奇怪的問題 . 我不時地動態更改了corePoolSize，我觀察到線程池沒有處理應該完成的任務 .

例如，如果我有4個corePoolSize并且隊列中有許多任務等待，那么執行程序最多處理3個，有時甚至是2個 .

在調查問題的時候，我注意到當我增加或減少corePoolSize時我從未改變過maxPoolSize . 從我的申請開始，它一直是1 .

從來沒有在Java的文檔中找到一個聲明，提到maxPoolSize的效果小于核心 .

然后當我檢查源代碼時，我注意到在costructor和setCorePoolSize方法中，它會檢查maximumPoolSize小于corePoolSize的位置，如果是這樣，則拋出illegalArgumentException . 看看下面的代碼 .

構造函數

public ThreadPoolExecutor(

int corePoolSize,

int maximumPoolSize,

long keepAliveTime,

TimeUnit unit,

BlockingQueue workQueue,

ThreadFactory threadFactory,

RejectedExecutionHandler handler

) {

if (corePoolSize < 0 ||

maximumPoolSize <= 0 ||

maximumPoolSize < corePoolSize ||

keepAliveTime < 0)

throw new IllegalArgumentException();

if (workQueue == null || threadFactory == null || handler == null)

throw new NullPointerException();

this.corePoolSize = corePoolSize;

this.maximumPoolSize = maximumPoolSize;

this.workQueue = workQueue;

this.keepAliveTime = unit.toNanos(keepAliveTime);

this.threadFactory = threadFactory;

this.handler = handler;

}

設置最大池大小

public void setMaximumPoolSize(int maximumPoolSize) {

if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize)

throw new IllegalArgumentException();

final ReentrantLock mainLock = this.mainLock;

mainLock.lock();

try {

int extra = this.maximumPoolSize - maximumPoolSize;

this.maximumPoolSize = maximumPoolSize;

if (extra > 0 && poolSize > maximumPoolSize) {

try {

Iterator it = workers.iterator();

while (it.hasNext() &&

extra > 0 &&

poolSize > maximumPoolSize) {

it.next().interruptIfIdle();

--extra;

}

} catch (SecurityException ignore) {

// Not an error; it is OK if the threads stay live

}

}

} finally {

mainLock.unlock();

}

}

所以，顯然這是一個不受歡迎的情況 . 但是沒有檢查setCorePoolSize，導致maximumPoolSize最終小于corePoolSize，并且沒有記錄這種情況的影響 .

設置核心池大小

public void setCorePoolSize(int corePoolSize) {

if (corePoolSize < 0)

throw new IllegalArgumentException();

final ReentrantLock mainLock = this.mainLock;

mainLock.lock();

try {

int extra = this.corePoolSize - corePoolSize;

this.corePoolSize = corePoolSize;

if (extra < 0) {

int n = workQueue.size(); // don't add more threads than tasks

while (extra++ < 0 && n-- > 0 && poolSize < corePoolSize) {

Thread t = addThread(null);

if (t == null)

break;

}

}

else if (extra > 0 && poolSize > corePoolSize) {

try {

Iterator it = workers.iterator();

while (it.hasNext() &&

extra-- > 0 &&

poolSize > corePoolSize &&

workQueue.remainingCapacity() == 0)

it.next().interruptIfIdle();

} catch (SecurityException ignore) {

// Not an error; it is OK if the threads stay live

}

}

} finally {

mainLock.unlock();

}

}

難道你不認為應該有一種機制阻止這種情況結束嗎？

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