Synchronization on the local variables

if (foo.needsProcessing()) {
    synchronized (foo) {
        foo.process();  // foo's state may be changed here
    }
}

I think there is a race condition in the above fragment that could result in foo.process() occasionally being called twice on the same object. It should be:

synchronized (foo) {
    if (foo.needsProcessing()) {
        foo.process();  // foo's state may be changed here
    }
}

Is this really that bad to synchronize on locals?

It is not bad to synchronize on locals per se. The real issues are:

• whether the different threads are synchronizing on the correct objects to achieve proper synchronization, and

• whether something else could cause problems by synchronizing on those objects.