构造器类在Java反射中的线程安全 [英] Constructor class thread safety in Java reflection

问题描述

使用 Java 反射，可以实例化类的对象，即使通过私有构造函数

Using Java reflection, one can instantiate an object of a class, even via a private constructor, e.g. for

public class MyClass
{
    private MyClass(Object p1, String p2)
    {
        // Constructor with no modifications to static code
    }
}

one can do (in the same or any other class, exception handling omitted for simplification)

public static final Constructor myClass;

static
{
    myClass = MyClass.class.getConstructor(Object.class, String.class);
    myClass.setAccessible(true);
}

，然后创建 MyClass like

and then create new instances of MyClass like

    myClass.newInstance(new Object(), "Test");

是上述调用 newInstance（）由于 myClass 是静态的

Is the above call to newInstance() thread-safe, given that myClass is static?

推荐答案

code> Constructor.newInstance（）似乎不是严格的线程安全的;至少在我的openjdk-6实现中，我发现一个类 sun.reflect.NativeConstructorAccessorImpl 有一个字段定义为 private int numInvocations; 和稍后在这行代码： if（++ numInvocations> ReflectionFactory.inflationThreshold（））{ - 这可能会如预期的行为。

同样，在 Constructor 类本身中，方法 acquireConstructorAccessor（）记录为这里没有同步。

Calling Constructor.newInstance() does not seem to be strictly thread-safe; at least in my openjdk-6 implementation I find a class sun.reflect.NativeConstructorAccessorImpl having a field defined as private int numInvocations; and later on this line of code: if (++numInvocations > ReflectionFactory.inflationThreshold()) { - which may certainly behave otherwise as expected.
Also, in the Constructor class itself, the method acquireConstructorAccessor() is documented with "NOTE that there is no synchronization used here".

但是，狡猾的行为似乎并没有导致一个完全意外的行为，只做重复/不必要的事情，因此调用 newInstance（）并行不会导致某些东西被破坏。

But the dodgy behaviour does not seem to result in an overall unexpected behavior, only doing things repeatedly/unnecessarily, thus calling newInstance() in parallel would NOT result in something being screwed up.

显然，你仍然可以实例构造函数。

Obviously, you can still mess things up with what's done within the instance constructor.

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