Jimmy,Jing Lv wrote:
Hi,
2009/7/9 Regis <xu.re...@gmail.com>
Regis wrote:
Regis Xu (JIRA) wrote:
[
https://issues.apache.org/jira/browse/HARMONY-6257?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel]
Regis Xu updated HARMONY-6257:
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Attachment: HARMONY-6257.diff
[classlib][luni] - Optimize OSMemory.get/setByteArray
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Key: HARMONY-6257
URL: https://issues.apache.org/jira/browse/HARMONY-6257
Project: Harmony
Issue Type: Improvement
Components: Classlib
Affects Versions: 5.0M10
Reporter: Regis Xu
Attachments: HARMONY-6257.diff
in getByteArray, use SetByteArrayRegion to avoid memory copy from java
to native
in setByteArray, Get/ReleasePrimitiveArrayCritical instead of
GetByteArrayElements/ReleaseByteArrayElements to avoid memory copy.
I just found in OSMemory.c, get/setByteArray do some unnecessary memory
copies between Java and native.
In getByteArray, GetByteArrayElements copy data from java to native, and
then ReleaseByteArrayElements do the reverse, I think using
SetByteArrayRegion is enough.
+1 for this fix
In setByteArray, I found JNI calls
GetPrimitiveArrayCritical/ReleasePrimitiveArrayCritical could get a pointer
to the primitive array without any copy, but seems they has some side
effects (on GC?), I don't have much confidence that they can apply here. I
hope some one can give some advices about this patch. Thanks.
According to HARMONY-1634, ReleasePrimitiveArrayCritical should be called every
time, whether "isCopy" is true or not. I'll update patch soon.
As I know, use this GetPrimitiveArrayCritical is something like entering the
"critical region", the spec reads:
After calling GetPrimitiveArrayCritical, the native code should not run for
an extended period of time before it calls ReleasePrimitiveArrayCritical. We
must treat the code inside this pair of functions as running in a "critical
region." Inside a critical region, native code must not call other JNI
functions, or any system call that may cause the current thread to block and
wait for another Java thread. (For example, the current thread must not call
read on a stream being written by another Java thread.)
thus it may potentially stall GC, as well as other jni critical section is
Maybe only critical section on the same primitive array would be blocked?
delayed, so this may cause another performance degradation.
In this case, the critical section is very small, it should not be a problem, I
think.
So the question is, how key is this improvement, and what benchmark show
its improvement? I am not sure, it may be in some environment/situations,
e.g. in some small heap environment, this modification may be a little
slower? We'd better do some more benchmarks?
Yes, I have tested on a internal benchmark, I can't say much details, but it
based on real complicated applications and heavily used
DirectByteBuffer.get/put(). And after this patch, it boost 2-3%.
It's also possible to write a micro benchmark, but as you said it's hard to
simulate all the environment/situations.
The patch passed all luni and nio tests, if no one objected, I'd like to
commit it.
--
Best Regards,
Regis.
--
Best Regards,
Regis.
