On 12/03/2010 11:52 PM, Mandy Chung wrote:
Fix for 6977034: Thread.getState() very slow
Webrev at:
http://cr.openjdk.java.net/~mchung/6977034/webrev.00/
Hi Mandy,
you can use Integer.highestOneBit instead of the loop.
Also, setMapElement should be a pure function, i.e without the side
effect on array.
In that case,
setMapElement(map, JVMTI_THREAD_STATE_TERMINATED, TERMINATED);
can be transformed to
map[JVMTI_THREAD_STATE_TERMINATED] = highestJVMTIStateBit(TERMINATED);
so the access to the array element is not far from the creation
of the array so the VM can remove array bound checks even if
highestJVMTIStateBit is not inlined.
This is an improvement to map a Thread's threadStatus field to
Thread.State. The VM updates the Thread.threadStatus field directly
at state transition with the value as defined in JVM TI [1]. The
java.lang.Thread.getState() implementation can directly access the
threadStatus value and do a direct lookup from an array of
Thread.State. The threadStatus value is a bit vector and we would
have to create an array of a minimum of 1061 (0x425) elements to do
direct mapping. I took the approach to use the first highest order
bit set to 1 in the masked threadStatus value as the index to the
Thread.State element and only caches 32 elements (could be fewer). I
wrote a micro-benchmark measuring the Thread.getState of a thread in
different state that shows 1.7X to 6X speedup (see below). There is
possibly some issue with my micro-benchmark that I didn't observe the
14X speed up as Doug did in his experiment. However, I'd like to get
this reviewed and pushed to the repository so that anyone can do more
experiment on the performance measurement.
Thanks
Mandy
P.S. The discussion on this thread can be found at [2] [3].
[1]
http://download.java.net/jdk7/docs/platform/jvmti/jvmti.html#GetThreadState
[2]
http://mail.openjdk.java.net/pipermail/core-libs-dev/2010-July/004567.html
[3]
http://mail.openjdk.java.net/pipermail/core-libs-dev/2010-August/004721.html
JDK 7 b120 (in ms) With fix (in ms) Speed up
main 46465 22772 2.04
NEW 50676 29921 1.69
RUNNABLE 42202 14690 2.87
BLOCKED 72773 12296 5.92
WAITING 48811 13041 3.74
TIMED_WAITING 45737 12849 3.56
TERMINATED 40314 16376 2.46
Rémi
