----- Original Message -----
From: "LvJimmy，Jing" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Sunday, April 29, 2007 5:24 PM
Subject: Re: problem about System.loadLibrary and object's address
> 2007/4/29, Tingpeng Wu <[EMAIL PROTECTED]>:
>> Hi, xiaofeng,
>>
>> 1. I also feel very unnatural to call it through MyRuntime class, but I
>> don't know how to call it directly. Since drlvm needs HotSpot to help it to
>> compile the java source code, if I don't call it though an instance, the
>> HotSpot couldn't distinguish it. If I let the Jit to add the free() call in
>> a future time, I will not need it any more.
>>
>
> :) Java static method can be called as SomeClass.StaticMethod, so your
> program can be written as (it is nothing related with compiler)
> public static void main(String[] args)
> {
> set(10);
> System.out.println(get());
> }
>
>> 2. I added an method named "unsigned int get_object_addr(jobject jobj)" in
>> object_handle.cpp to return the address of jobj . I can call it directly to
>> get the object address in free() method. Since I could not assure whether it
>> can get the right address, so I add the get_obj_addr() for test purpose. I
>> will delete it if it can work corredtly.
>>
>
> Ah, I don't catch well here. Why do you need a free() function here?
> If you alloc a java object (no matter in java or native), you can just
> leave it alone and let GC do everything for you. Free() is too c-style
> for Java developer :)
> In the other way, if you want to alloc some memory for other use, for
> an example, char array in c/c++, you can just keep its address(you can
> keep a jlong as void* ) and free it at last(you'd better free in this
> case or you'll get memory leak). It is such easier to keep/pass a
> jlong value than jobject handle.
>
My thesis is to redesign the heap layout, and provide the free() method to
support reclaiming the object explicitly. Then in jit module, I will add some
analysis to insert some free call to reclaim the dead object in advance. The
purpose is to try to improve the efficiency of program's execution.
>
>> 3. Another quesetion: where is runtime helper you speak of? I am afraid I
>> need do some investigation on it.
>>
>> Thanks,
>> tingpeng
>> ----- Original Message -----
>> From: "Xiao-Feng Li" <[EMAIL PROTECTED]>
>> To: <[email protected]>
>> Sent: Sunday, April 29, 2007 4:05 PM
>> Subject: Re: problem about System.loadLibrary and object's address
>>
>>
>> > Tingpeng,
>> >
>> > 1. Your native is static native, why do you call it through an instance?
>> > 2. You probably need to use runtime helper for the object direct free
>> > in Java app, because the default JNI call path will save the object
>> > handle (and passes the reference address as a root entry during GC
>> > enumeration). For your purpose, there is no GC happening in free(),
>> > so it probably works with a stale object reference (freed) in the
>> > object handle.
>> > 3. You can use free() directly to retrieve its object address from the
>> > handle. Why do you need the get_obj_addr() method?
>> >
>> > Thanks,
>> > xiaofeng
>> >
>> > On 4/29/07, Tingpeng Wu <[EMAIL PROTECTED]> wrote:
>> >> Thanks, xiaofeng,
>> >> My test program is simple as follows:
>> >>
>> >> public class JNItest
>> >>
>> >> {
>> >>
>> >> static
>> >>
>> >> {
>> >>
>> >> System.loadLibrary("goodluck");
>> >>
>> >> }
>> >>
>> >>
>> >>
>> >> public native static int get();
>> >>
>> >> public native static void set(int i);
>> >>
>> >>
>> >>
>> >> public static void main(String[] args)
>> >>
>> >> {
>> >>
>> >> JNItest test = new JNItest();
>> >>
>> >> test.set(10);
>> >>
>> >> System.out.println(test.get());
>> >>
>> >> }
>> >>
>> >> }
>> >>
>> >> Then I use javah to produce JNItest.h and implement two method in
>> >> JNItest.cpp. Then use them to build goodluck.dll. I use the latest verson
>> >> of drlvm to test it, there is still an error which reports "Vm launcher
>> >> meets error and needs shut up (this is translated from chinese)".
>> >>
>> >> The reason I asked the second problem is I want to get the address of obj
>> >> in java to support the reclaimation. I plan to
>> >> MyRuntime class, which has a native method,
>> >> My thought now is as follows:
>> >> 1. provide a new class named MyRuntime which has two native methods.
>> >> class MyRuntime
>> >> {
>> >> static
>> >> {
>> >> System.loadLibrary("runtime");
>> >> }
>> >>
>> >> //public native static void alloc(……);
>> >>
>> >> public native static void get_obj_addr(Object obj);
>> >>
>> >> //public native static void free(Object obj);
>> >> }
>> >>
>> >> 2. export the get_object_addr(jobject jobj) in vmcore to support
>> >> MyRuntime.get_obj_addr(Object obj)
>> >> 3. export the free(unsigned size, void* address) in gc to support
>> >> MyRuntime.free(Object obj)
>> >> 4. if above is right, I can call MyRuntime.free(obj) in java method.
>> >>
>> >>
>> >>
>> >> Is it feasible to get address that way to support the reclaimation method?
>> >>
>> >> Thanks,
>> >> tingpeng
>> >>
>> >> ----- Original Message -----
>> >> From: "Xiao-Feng Li" <[EMAIL PROTECTED]>
>> >> To: <[email protected]>
>> >> Sent: Sunday, April 29, 2007 11:06 AM
>> >> Subject: Re: problem about System.loadLibrary and object's address
>> >>
>> >>
>> >> > Tingpeng, can you post your program if there is no legal issue? (e.g.,
>> >> > open a JIRA issue and attach your code there).
>> >> >
>> >> > For your second question, itis pretty the core part of JVM native
>> >> > interface design. Yes, the handle is used to access Java object
>> >> > indirectly. The idea is to support object movement during GC, then the
>> >> > real new address of the same object can be stored to the handle. It's
>> >> > not supposed to be used everywhere in the JVM, because that may break
>> >> > the protocol of JNI, causing GC to fail to update the object new
>> >> > address, e.g., if it is put into a register by your C compiler. You
>> >> > can access it in two ways: either always use JNI interface, or
>> >> > guarantee there is GC happening when you access it.
>> >> >
>> >> > Thanks,
>> >> > xiaofeng
>> >> >
>> >> > On 4/29/07, 吴廷鹏 <[EMAIL PROTECTED]> wrote:
>> >> >> Hi, all,
>> >> >> when I use drlvm to execute my program, I found that when program has
>> >> >> System.loadLibrary call, there is always an error which reports
>> >> >> "java.lang.outofmemoryerror <no stack trace available>". The same
>> >> >> program can run on Hotspot. Why this happens and how to solve it?
>> >> >>
>> >> >> Another question, I read the implementation code of Object.clone
>> >> >> method in Object_generic.cpp.
>> >> >>
>> >> >> jobject object_clone(JNIEnv *jenv, jobject jobj)
>> >> >> {
>> >> >> ObjectHandle h = (ObjectHandle) jobj;
>> >> >>
>> >> >> //aquire the target address and assign it to variable named result
>> >> >>
>> >> >> memcpy(result, h->object, size);
>> >> >>
>> >> >> }
>> >> >> According to my comprehension, h->object is the address of java
>> >> >> object. Is it ture? Does this means I can use the same way to get the
>> >> >> address of object in vmcore's other place provided the necessary head
>> >> >> file is included?
>> >> >>
>> >> >> Thanks,
>> >> >> tingpeng
>> >> >>
>> >> >
>> >> >
>> >> > --
>> >> > http://xiao-feng.blogspot.com
>> >> >
>> >
>> >
>> > --
>> > http://xiao-feng.blogspot.com
>> >
>
>
> --
>
> Best Regards!
>
> Jimmy, Jing Lv
> China Software Development Lab, IBM
>
