URGENT (XS) RFR: 8149697: Fix for 8145725 is broken

[Daniel D. Daugherty]

Thumbs up!

Dan


On 2/11/16 1:37 PM, David Holmes wrote:
> bug: https://bugs.openjdk.java.net/browse/JDK-8149697
>
> webrev: http://cr.openjdk.java.net/~dholmes/8149697/webrev/
>
> In the refactoring for 8145725 a check of _cur_index was moved outside 
> the mutex block, but this was wrong as the value could be changed by a 
> parking thread. As per the existing comment we needed to check the 
> saved 'index' instead:
>
> --- old/src/os/linux/vm/os_linux.cpp    2016-02-11 15:23:59.696802390 
> -0500
> +++ new/src/os/linux/vm/os_linux.cpp    2016-02-11 15:23:57.440675175 
> -0500
> @@ -5756,7 +5756,7 @@
>    int index = _cur_index;
>    status = pthread_mutex_unlock(_mutex);
>    assert_status(status == 0, status, "invariant");
> -  if (s < 1 && _cur_index != -1) {
> +  if (s < 1 && index != -1) {
>      // thread is definitely parked
>      status = pthread_cond_signal(&_cond[index]);
>      assert_status(status == 0, status, "invariant");
>
> This could introduce spurious wakeups for a parking thread.
>
> Thanks,
> David