[英]Java Lock Condition Wait and Notify: IllegalMonitorStateException
I am new to Java. 我是Java新手。 I just read the "core java" book.
我刚刚读了“核心Java”书。 I met a issue about 'Condition & Lock'.
我遇到了有关“条件与锁定”的问题。
I typed a piece of code from the book to the eclipse to do some practice. 我输入了从书本到日食的一段代码来进行一些练习。
When I run the code ,the line of "sufficientFund.wait();" 当我运行代码时,“ sufficientFund.wait();”行 throws an IllegalMonitorStateException.
引发IllegalMonitorStateException。 Why here has an exception?
为什么这里有例外?
I hava googled for a while, I know that "This method should only be called by a thread that is the owner of this object's monitor." 我已经搜索了一段时间,我知道“该方法只能由作为该对象监视器的所有者的线程调用。” I think the current thread has the lock, because the 'bankLock.lock();'
我认为当前线程具有锁定,因为“ bankLock.lock();” is executed just before wait().
在wait()之前执行。 I think the correct behavior of the code is, the current thread should be hung at the sufficientFund.wait(), but it didn't.
我认为代码的正确行为是,当前线程应该挂在足够的Fund.wait()上,但事实并非如此。
package com.first.java;
import java.util.Scanner;
import java.util.concurrent.locks.*;
public class BankTranf {
private static final int NACCOUNT = 3;
public static final double INITAL_BALANCE = 1000;
public static void main(String[] args) {
Bank bank = new Bank(NACCOUNT, INITAL_BALANCE);
for (int i = 0; i < NACCOUNT; i++) {
TransferRunnable transferRunnable = new TransferRunnable(bank, i, INITAL_BALANCE);
Thread thread = new Thread(transferRunnable);
thread.start();
}
System.out.println("press any key to exit.");
Scanner in = new Scanner(System.in);
in.nextLine();
System.exit(0);
}
}
class Bank {
private final double[] account;
private Lock bankLock;
private Condition sufficientFund;
public Bank(int n, double initialBanlance) {
account = new double[n];
for (int i = 0; i < account.length; i++) {
account[i] = initialBanlance;
}
bankLock = new ReentrantLock();
sufficientFund = bankLock.newCondition();
}
public void transfer(int from, int to, double amount) {
bankLock.lock();
try {
while (account[from] < amount) {
System.out.println(Thread.currentThread().getName() + " does'nt hava enough money");
sufficientFund.wait();
}
System.out.println(Thread.currentThread());
account[from] -= amount;
System.out.printf("%10.2f from %d to %d ", amount, from, to);
account[to] += amount;
System.out.printf(" Total balance: %10.2f%n", getTotalBalance());
sufficientFund.signalAll();
} catch (Exception ex) {
ex.printStackTrace();
} finally {
bankLock.unlock();
}
}
public double getTotalBalance() {
double d = 0;
bankLock.lock();
try {
for (double n : account) {
d += n;
}
return d;
} finally {
bankLock.unlock();
}
}
public int size() {
return account.length;
}
}
class TransferRunnable implements Runnable {
private Bank bank;
private int fromAccount;
private double maxAmount;
private int DELAY = 10;
public TransferRunnable(Bank b, int from, double max) {
bank = b;
this.fromAccount = from;
this.maxAmount = max;
}
@Override
public void run() {
try {
while (true) {
int toAcount = (int) (bank.size() * Math.random());
double amount = maxAmount * Math.random();
bank.transfer(fromAccount, toAcount, amount);
Thread.sleep(4000/* (int)(DELAY*Math.random()) */);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
I also tried another way, I remove all the Lock and Condition, instead of using "synchronized", the code was running as I expected. 我还尝试了另一种方法,即删除了所有的Lock和Condition,而不是使用“ synchronized”,而是代码按预期运行。
public synchronized void transfer(int from, int to, double amount) {
//bankLock.lock();
try {
while (account[from] < amount) {
System.out.println(Thread.currentThread().getName() + " does'nt hava enough money");
wait();
}
System.out.println(Thread.currentThread());
account[from] -= amount;
System.out.printf("%10.2f from %d to %d ", amount, from, to);
account[to] += amount;
System.out.printf(" Total balance: %10.2f%n", getTotalBalance());
notifyAll();
} catch (Exception ex) {
ex.printStackTrace();
} finally {
}
}
public synchronized double getTotalBalance() {
double d = 0;
try {
for (double n : account) {
d += n;
}
return d;
} finally {
}
}
请注意, Condition
作为Java中的任何类都扩展了Object
,因此它具有从Object
继承的wait
方法,我相信您在这里错误地调用了该方法,您要在条件上等待的方法是Condition#await
而不是wait
。
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