Java多线程同步块循环
我实现了示例程序,以确保每次执行特定进程的线程不超过5个。但结果并不像预期的那样Java多线程同步块循环,java,multithreading,thread-safety,thread-synchronization,Java,Multithreading,Thread Safety,Thread Synchronization,我实现了示例程序,以确保每次执行特定进程的线程不超过5个。但结果并不像预期的那样 public class MiscUtils{ private volatile static int count = 0; public synchronized static int getCount() { return count; } public synchronized static boolean incrementCounter() thro
public class MiscUtils{
private volatile static int count = 0;
public synchronized static int getCount() {
return count;
}
public synchronized static boolean incrementCounter() throws InterruptedException {
System.out.println("count - " + count);
while(MiscUtils.getCount() > 4) {
System.out.println(Thread.currentThread().getName() + " Sleeping..");
Thread.sleep(1000 * 5);
}
System.out.println("Thread acquired " + Thread.currentThread().getName());
if(count > 4) {
return false;
}
count++;
return true;
}
public synchronized static boolean decrementCounter() {
System.out.println("Decrement Called " + Thread.currentThread().getName());
count--;
return true;
}
public static void main(String[] args) throws InterruptedException {
Runnable r = new Runnable() {
@Override
public void run() {
try {
//System.out.println(new Date() + " :: Thread incremented");
MiscUtils.incrementCounter();
Thread.sleep(10 * 1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
MiscUtils.decrementCounter();
System.out.println(Thread.currentThread().getName());
}
};
int count = 10;
for(int i = 0; i < count; i++) {
Thread s = new Thread(r);
System.out.println(new Date() + "Thread " + i + " starting..");
s.start();
System.out.println(new Date() + "Thread " + i + " started..");
Thread.sleep(1 * 1000);
}
}
}
预期产量-
Mon Dec 30 19:29:20 IST 2019Thread 0 starting..
Mon Dec 30 19:29:20 IST 2019Thread 0 started..
count - 0
Thread acquired Thread-0
Mon Dec 30 19:29:21 IST 2019Thread 1 starting..
Mon Dec 30 19:29:21 IST 2019Thread 1 started..
count - 1
Thread acquired Thread-1
Mon Dec 30 19:29:22 IST 2019Thread 2 starting..
Mon Dec 30 19:29:22 IST 2019Thread 2 started..
count - 2
Thread acquired Thread-2
Mon Dec 30 19:29:23 IST 2019Thread 3 starting..
Mon Dec 30 19:29:23 IST 2019Thread 3 started..
count - 3
Thread acquired Thread-3
Mon Dec 30 19:29:24 IST 2019Thread 4 starting..
Mon Dec 30 19:29:24 IST 2019Thread 4 started..
count - 4
Thread acquired Thread-4
Mon Dec 30 19:29:25 IST 2019Thread 5 starting..
Mon Dec 30 19:29:25 IST 2019Thread 5 started..
count - 5
Thread-5 Sleeping..
Mon Dec 30 19:29:26 IST 2019Thread 6 starting..
Mon Dec 30 19:29:26 IST 2019Thread 6 started..
Mon Dec 30 19:29:27 IST 2019Thread 7 starting..
Mon Dec 30 19:29:27 IST 2019Thread 7 started..
Mon Dec 30 19:29:28 IST 2019Thread 8 starting..
Mon Dec 30 19:29:28 IST 2019Thread 8 started..
Mon Dec 30 19:29:29 IST 2019Thread 9 starting..
Mon Dec 30 19:29:29 IST 2019Thread 9 started..
Thread-5 Sleeping..
Thread-5 Sleeping..
Thread acquired Thread-5
Thread-6 Sleeping..
Thread acquired Thread-6
and so on...
从未调用DecrementCounter方法。另外,我希望同步块应该更新getCount方法中的count变量,以获取最新的值。但它总是返回值5。
请告诉我哪里出了问题。当您在类中同步静态方法时,这意味着它们都锁定在同一个监视器上,该监视器就是类本身
因此,当线程5进入while循环时,它将无限期地保持锁,而线程1-4仍在等待获取锁以进入递减计数器。代码的主要问题如下: 在Java中,同一个类中只有一个线程可以在静态同步方法内执行。[] 这意味着您的线程将在开始时保持MiscUtils.incrementCounter的执行。 它还将阻止MiscUtils.decrementCounter的执行。 计数达到值5后,线程-5将卡在循环中,而iscutils.getCount>4 然后,thread-5之后的所有线程都将启动,但将进入睡眠状态,因为同步静态方法MiscUtils.incrementCounter仍然与thread-5保持一致。 这肯定会导致无限循环
我希望这是一个明确的答案。该代码在MiscUtils中调用静态函数,您也可以添加该代码吗?第一块代码在名为MiscUtils的类中。。它引用的是相同的类静态方法..我想我需要重温java书籍DUnrelated,但也有一个错误:即使MiscUtils.incrementCounter返回false,也会调用MiscUtils.decrementCounter。是。那正是我被打动的地方。正如@Adwait所回答的,必须成功执行MiscUtils.incrementCounter,才能调用MiscUtils.decrementCounter。。
Mon Dec 30 19:29:20 IST 2019Thread 0 starting..
Mon Dec 30 19:29:20 IST 2019Thread 0 started..
count - 0
Thread acquired Thread-0
Mon Dec 30 19:29:21 IST 2019Thread 1 starting..
Mon Dec 30 19:29:21 IST 2019Thread 1 started..
count - 1
Thread acquired Thread-1
Mon Dec 30 19:29:22 IST 2019Thread 2 starting..
Mon Dec 30 19:29:22 IST 2019Thread 2 started..
count - 2
Thread acquired Thread-2
Mon Dec 30 19:29:23 IST 2019Thread 3 starting..
Mon Dec 30 19:29:23 IST 2019Thread 3 started..
count - 3
Thread acquired Thread-3
Mon Dec 30 19:29:24 IST 2019Thread 4 starting..
Mon Dec 30 19:29:24 IST 2019Thread 4 started..
count - 4
Thread acquired Thread-4
Mon Dec 30 19:29:25 IST 2019Thread 5 starting..
Mon Dec 30 19:29:25 IST 2019Thread 5 started..
count - 5
Thread-5 Sleeping..
Mon Dec 30 19:29:26 IST 2019Thread 6 starting..
Mon Dec 30 19:29:26 IST 2019Thread 6 started..
Mon Dec 30 19:29:27 IST 2019Thread 7 starting..
Mon Dec 30 19:29:27 IST 2019Thread 7 started..
Mon Dec 30 19:29:28 IST 2019Thread 8 starting..
Mon Dec 30 19:29:28 IST 2019Thread 8 started..
Mon Dec 30 19:29:29 IST 2019Thread 9 starting..
Mon Dec 30 19:29:29 IST 2019Thread 9 started..
Thread-5 Sleeping..
Thread-5 Sleeping..
Thread acquired Thread-5
Thread-6 Sleeping..
Thread acquired Thread-6
and so on...