[RFC]: Linkage Error fix.

[Andrew Haley]

On 15/04/11 20:55, Deepak Bhole wrote:

> Did you look into how URLCloassLoader and others mitigate the problem?
> If I am not mistaken, all class load requests go through JNLPClassLoader,
> and synchronizing on each such call can get expensive.

In 1.6 ClassLoader.loadClass() is a synchronized method anyway.

There's something of a myth about the expense of synchronization that
isn't usually justified by actual measurements.  It's usually only a
compareAndSwap, and there is little pain for uncontended cases.
Avoiding synchronization with more complex schemes may actually be
slower; you have to measure it.

> OTOH, if URLClassLoader is doing the same, we are not impacting the
> performance any further so it'd be okay.

This is exactly how ClassLoader does it in 1.7.  However,
ClassLoader's code is a bit more clear:

    protected Class<?> loadClass(String name, boolean resolve)
        throws ClassNotFoundException
    {
        synchronized (getClassLoadingLock(name)) {

where

    protected Object getClassLoadingLock(String className) {
        Object lock = this;
        if (parallelLockMap != null) {
            Object newLock = new Object();
            lock = parallelLockMap.putIfAbsent(className, newLock);
            if (lock == null) {
                lock = newLock;
            }
        }
        return lock;
    }

Andrew.