2007/4/29, Tingpeng Wu <[EMAIL PROTECTED]>:
----- 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.
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. :)
> >> 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 >
-- Best Regards! Jimmy, Jing Lv China Software Development Lab, IBM
