Re: [libvirt] Memory free in libvirt JNA
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@av-test.de]
Sent: 2012年10月11日 23:36
To: Benjamin Wang (gendwang)
Cc: veillard(a)redhat.com; libvir-list(a)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.
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