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From "Tingpeng Wu" <wutingp...@gmail.com>
Subject Re: problem about System.loadLibrary and object's address
Date Sun, 29 Apr 2007 12:51:46 GMT
xiaofeng, very thank you for your help and valuable time. I will try your suggestion next.
----- Original Message ----- 
From: "Xiao-Feng Li" <xiaofeng.li@gmail.com>
To: <dev@harmony.apache.org>
Sent: Sunday, April 29, 2007 8:36 PM
Subject: Re: problem about System.loadLibrary and object's address


> On 4/29/07, LvJimmy,Jing <firepure@gmail.com> wrote:
>> 2007/4/29, Tingpeng Wu <wutingpeng@gmail.com>:
>> >
>> > ----- Original Message -----
>> > From: "LvJimmy,Jing" <firepure@gmail.com>
>> > To: <dev@harmony.apache.org>
>> > Sent: Sunday, April 29, 2007 5:24 PM
>> > Subject: Re: problem about System.loadLibrary and object's address
>> >
>> >
>> > > 2007/4/29, Tingpeng Wu <wutingpeng@gmail.com>:
>> > >> 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.
>> >
>>
>> Got it, I remember we've already discussed this problem (free() in
>> java) and IIRC, some expert mark this problem as "mission impossible"
>> ... :)
>> However study something about GC may benefit your thesis. :)
> 
> Jimmy, it's possible to insert free() automatically in jitted code to
> reclaim some short-lived objects. This can be a supplementary to the
> GC, and probably improve the overall performance. Tingpeng had
> previous discussions with me on this topic actually.
> 
> TingPeng, the runtime helper is a way in DRLVM for the VM to provide
> JIT certain supports, e.g.,  exception throwing, etc.  One of the
> important usages of runtime helper is to provide a way of fast native
> method invocation. That is, when you know a native method never causes
> GC, you probably can use a runtime helper for JIT to generate code to
> invoke this native method directly without going through the JNI
> stuff. This makes native call fast.
> 
> You can find runtime helper code in jit_runtime_support related files.
> Please go search VM_RT_AASTORE in vm source code, you will see in
> vmcore/src/util/ia32/base/jit_runtime_support_ia32.cpp how aastore can
> implemented in native code to support JIT.    VM_RT_GC_HEAP_WRITE_REF
> is an example for write barrier native implementation
> gc_heap_slot_write_ref().
> 
> Please let me know if you have any further questions.
> 
> Thanks. xiaofeng
> 
>> > >
>> > >> 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" <xiaofeng.li@gmail.com>
>> > >> To: <dev@harmony.apache.org>
>> > >> 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 <wutingpeng@gmail.com> 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" <xiaofeng.li@gmail.com>
>> > >> >> To: <dev@harmony.apache.org>
>> > >> >> 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 <wutingpeng@gmail.com> 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
>> > >
>>
>>
>> --
>>
>> Best Regards!
>>
>> Jimmy, Jing Lv
>> China Software Development Lab, IBM
>>
> 
> 
> -- 
> http://xiao-feng.blogspot.com
>
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