[libvirt] Memory free in libvirt JNA
Benjamin Wang (gendwang)
gendwang at cisco.com
Fri Oct 12 02:05:08 UTC 2012
Hi Claudio,
Thanks for you informing about new JNA version. I try to use JNA provided API. It works well. The updated code is as following:
public SchedParameter[] getSchedulerParameters() throws LibvirtException {
IntByReference nParams = new IntByReference();
SchedParameter[] returnValue = new SchedParameter[0];
- String scheduler = libvirt.virDomainGetSchedulerType(VDP, nParams);
+ Pointer pScheduler = libvirt.virDomainGetSchedulerType(VDP,
+ nParams);
processError();
- if (scheduler != null) {
+ if (pScheduler != null) {
+ String scheduler = pScheduler.getString(0);
+ Native.free(Pointer.nativeValue(pScheduler));
virSchedParameter[] nativeParams = new virSchedParameter[nParams.getValue()];
returnValue = new SchedParameter[nParams.getValue()];
libvirt.virDomainGetSchedulerParameters(VDP, nativeParams, nParams);
If there is no issue. I recommend to use this solution to enhance all JNA code.
BTW:
Not all the returned String should be freed by JNA. For example, In Domain Class, the result returned by the method getName/ getUUIDString
can't be freed. Because the reference were not allocated temporarily. We must analyze case by case.
B.R.
Benjamin Wang
-----Original Message-----
From: Claudio Bley [mailto:cbley at av-test.de]
Sent: 2012年10月11日 23:36
To: Benjamin Wang (gendwang)
Cc: veillard at redhat.com; libvir-list at redhat.com; Yang Zhou (yangzho)
Subject: Re: [libvirt] Memory free in libvirt JNA
At Thu, 11 Oct 2012 08:37:23 +0000,
Benjamin Wang (gendwang) wrote:
>
> Hi Claudio,
> Sorry for my late response.
> I have gone through Claudio's solution. It's good. But I think this is not a common solution. There are two points:
> 1. This solution must use Pointerbyreference to encapsulate the
> Pointer. This is not clean.
Yes, as I said, this adds another level of indirection --- which is pretty useless in Java.
> 2. Libvirt provides virFree method. But a common library could not
> provide memory management functions.
Sorry, I don't get your point here.
> My proposal is as following:
> 1. Add a new Class Libc.java
> public interface Libc extends Library{
> Libc INSTANCE = (Libc) Native.loadLibrary("c", Libc.class);
>
> public void free(Pointer p);
> }
Not every platform has a shared library called "c". On Windows this would be msvcrt.dll for the Microsoft runtime. So, you would need to branch on the platform to load whatever library seems appropriate.
Also, I just discovered that since version 3.3.0 JNA provides a public free method itself.
Since I get crashes when using callback functions with JNA 3.2.7 in certain circumstances it is better just to require a newer version of JNA, IMHO.
I'll post a few patches with improvements and memory fixes tomorrow.
--
AV-Test GmbH, Henricistraße 20, 04155 Leipzig, Germany
Phone: +49 341 265 310 19
Web:<http://www.av-test.org>
Eingetragen am / Registered at: Amtsgericht Stendal (HRB 114076) Geschaeftsfuehrer (CEO): Andreas Marx, Guido Habicht, Maik Morgenstern
More information about the libvir-list
mailing list