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我正在为我的应用程序实现网络线程管理器。我创建了一个JUnit测试,迅速请求,并通过调用下面两个方法释放一个网线指标:Java同步帮助请求
protected static final List <Integer> currThreads = new ArrayList <Integer>();
protected static int maxThreads = 5;
protected static int lastGrantedId = 0;
public static synchronized int reqNewThread(){
if (currThreads.size() >= maxThreads) return -1;
++lastGrantedId;
currThreads.add(lastGrantedId);
return lastGrantedId;
}
public static void threadFinished(final int threadId) throws InternalError{
if (threadId == -1) return;
synchronized (currThreads) {
boolean works = currThreads.remove(Integer.valueOf(threadId));
assert works : ("threadId: " + threadId);
}
}
线程完成自己的工作后,currThreads
不是空的,但reqNewThread
和threadFinished
具有相同的调用次数和remove()
总是产生true
。如果我同步整个threadFinished
方法,它工作正常。问题是 - 为什么?唯一使用的全局变量已经同步了,不是吗?
JUnit4测试代码:
final int iters = 15;
final Runnable getAndFree = new GetAndFree(iters);
final int sz = 15;
final Thread[] t = new Thread[sz];
for (int i = 0; i < sz; i++)
t[i] = new Thread(getAndFree);
for (int i = 0; i < sz; i++)
t[i].start();
for (int i = 0; i < sz; i++)
t[i].join();
assertEquals(0, currThreads.size());
仪线程来源:
private class GetAndFree implements Runnable {
int iters;
public GetAndFree(int iters){
this.iters = iters;
}
@Override
public void run(){
try {
int id = -1;
for (int i = 0; i < iters; i++) {
while ((id = reqNewThread()) == -1) {
Thread.sleep(25);
};
System.out.println("Strarted: " + id);
Thread.sleep((long)(Math.random() * 10));
threadFinished(id);
System.out.println("Finished: " + id);
} // for
} catch(final Exception ex) {
ex.printStackTrace();
}
}
}
确实。谢谢:)我是个白痴。我会尽快接受你的回答。 – 2011-04-08 10:36:47