java.lang.IllegalMonitorStateException:(m = null)无法获取监视器

问题描述

为什么会发生这种情况?事实是，监视器对象肯定不是null，但仍然经常会遇到此异常:

Why may this happen? The thing is that monitor object is not null for sure, but still we get this exception quite often:

java.lang.IllegalMonitorStateException: (m=null) Failed to get monitor for (tIdx=60)
        at java.lang.Object.wait(Object.java:474)
        at ...

引发此问题的代码是一个简单的池解决方案:

The code that provokes this is a simple pool solution:

    public Object takeObject() {
        Object obj = internalTakeObject();
        while (obj == null) {
            try {
                available.wait();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            obj = internalTakeObject();
        }
        return obj;
    }

    private Object internalTakeObject() {
        Object obj = null;
        synchronized (available) {
            if (available.size() > 0) {
                obj = available.keySet().iterator().next();
                available.remove(obj);
                synchronized (taken) {
                    taken.put(obj, Boolean.valueOf(true));
                }
            }
        }
        return obj;
    }

    public void returnObject(Object obj) {
        synchronized (taken) {
            taken.remove(obj);
        }
        synchronized (available) {
            if (available.size() < size) {
                available.put(obj, Boolean.valueOf(true));
                available.notify();
            }
        }
    }

我想念什么吗?

编辑:该异常发生在available.wait();行中.

EDIT: The exception happens in available.wait(); line.

推荐答案

有关Object.wait的信息，请参见javadoc.

See the javadoc for Object.wait.

尤其是当前线程必须拥有该对象的监视器."和"[throws] IllegalMonitorStateException-如果当前线程不是对象监视器的所有者."也就是说，您需要在将要调用的对象上进行同步.

in particular "The current thread must own this object's monitor." and "[throws] IllegalMonitorStateException - if the current thread is not the owner of the object's monitor." That is, you need to synchronize on the object you are going to call wait on.

因此您的代码应为:

synchronized (available) {
    available.wait();
}

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