review request for 6791815

[David Holmes - Sun Microsystems]

Looks good to me.

Thanks,
David

Xiaobin Lu said the following on 01/13/09 09:44:
> 6791815:  Fix for 6471657 can cause deadlock on non-Solaris platforms 
> when initializing direct buffer support
> 
> Webrev: http://webrev.invokedynamic.info/xiaobin.lu/6791815/webrev/
> 
> Details:
> 
> When mutiple threads call NewDirectByteBuffer using JNI, deadlock could 
> occur when thread A triggers the safepoint and thread B is busy waiting 
> for thread A to get finished. However, the current implementation 
> transfers thread B's state to be in VM state due to the fact that 
> os::yield_all call could result into a os::sleep call on Solaris. The 
> side effect of put thread B's state to be in VM state is that the 
> VMThread will wait for thread B to finish before putting all Java 
> threads to sleep. However, thread B is waiting for thread A to finish 
> and thread A is waiting for the VMThread to return. Hence, a deadlock 
> occurs.
> 
> The fix suggested by Tom is to put the ThreadInVMfromNative statement 
> inside the loop so that there is a Window that thread B could change 
> back its state to native and as a result, the VMThread could proceed to 
> bring all the threads to safepoint. This is based on the fact that 
> VMThread doesn't stop threads in native, the state check only occurs 
> during the state transition.
> 
> I've tried hard to come up a local test to reproduce the problem, but 
> without much luck. I have contacted the reporter so that I can give him 
> the VM to verify that the problem has been fixed. I am pretty sure it 
> has, but just to be safe.
> 
> Thanks,
> -Xiaobin
>