Re: [libvirt] Memory free in libvirt JNA
Hi,
I wrote a code to verify the memory leak problem as following.
C code in so:
void checkJNAMemLeak1(int **head, int *length)
{
long i = 0;
*head = (int *)malloc(sizeof(int) * 100000000);
for(i=0; i<100000000; i++)
{
(*head)[i] = 1;
}
*length = 100000000;
}
Java code:
public static void testJNAMemLeak1()
{
PointerByReference head = new PointerByReference();
IntByReference length = new IntByReference();
while(true)
{
libben.checkJNAMemLeak1(head, length);
System.out.println(length.getValue());
sleep(1);
}
}
When we check memory by top command, the virt and res will increase very quickly. When we
check with jconsole, there is no memory in Java heap. Even I execute GC manually by
jconsole. Nothing happen.
If I change java code as following:
public static void testJNAMemLeak1()
{
PointerByReference head = new PointerByReference();
IntByReference length = new IntByReference();
while(true)
{
libben.checkJNAMemLeak1(head, length);
System.out.println(length.getValue());
sleep(1);
libc.free(head.getValue());
}
}
public static void testJNAMemLeak1()
{
PointerByReference head = new PointerByReference();
IntByReference length = new IntByReference();
while(true)
{
libben.checkJNAMemLeak1(head, length);
System.out.println(length.getValue());
sleep(1);
libc.free(head.getValue());
}
}
Then everything works well. The virt and res will not increase.
I think we must provide the free functions for all the memory allocated by libvirt.
B.R.
Benjamin Wang
-----Original Message-----
From: Benjamin Wang (gendwang)
Sent: 2012年9月7日 15:22
To: libvir-list(a)redhat.com
Cc: 'veillard(a)redhat.com'; Yang Zhou (yangzho)
Subject: RE: Memory free in libvirt JNA
Hi,
Overview Part of JNA API describes as following:
1. Description1:
If the native method returns char* and actually allocates memory, a return type of Pointer
should be used to avoid leaking the memory. It is then up to you to take the necessary
steps to free the allocated memory.
2. Description2:
Declare the method as returning a Structure of the appropriate type, then invoke
Structure.toArray(int) to convert to an array of initialized structures of the appropriate
size. Note that your Structure class must have a no-args constructor, and you are
responsible for freeing the returned memory if applicable in whatever way is appropriate
for the called function.
And the example code shows as following:
// Original C code
struct Display* get_displays(int* pcount); void free_displays(struct Display* displays);
// Equivalent JNA mapping
Display get_displays(IntByReference pcount); void free_displays(Display[] displays); ...
IntByReference pcount = new IntByReference(); Display d = lib.get_displays(pcount);
Display[] displays = (Display[])d.toArray(pcount.getValue());
...
lib.free_displays(displays);
That's to say. All the memory allocated by native code must be freed explicitly in JNA
part. We must add some free memory methods to support the memory-freeing.
Any comments?
B.R.
Benjamin Wang
-----Original Message-----
From: Daniel Veillard [mailto:veillard@redhat.com]
Sent: 2012年8月20日 14:25
To: Benjamin Wang (gendwang)
Cc: stoty(a)tvnet.hu; Daniel.Schwager(a)dtnet.de
Subject: Re: Memory free in libvirt JNA
On Mon, Aug 20, 2012 at 05:15:45AM +0000, Benjamin Wang (gendwang) wrote:
Hi Veillard,
Thanks for your reply. I checked the current Libvirt-JNA
implementation. I find that a method named "free" defined in Domain
class which is used to free the domain object. If this is mandatory, that's to say,
we should a lot of methods into the current Libvirt-jna implementation to free the memory
which is allocated by libvirt API. Please correct me!
As far as I understat free() is aliased as finalize() on that object so the java runtime
will call free() automatically on garbage collection. I'm not a java expert, check
some Java litterature for more details about how this is done and the cases where
free() might be better called directly.
Daniel
--
Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
daniel(a)veillard.com | Rpmfind RPM search engine http://rpmfind.net/ http://veillard.com/
| virtualization library http://libvirt.org/