xiaofeng, very thank you for your help and valuable time. I will try your suggestion next. ----- Original Message ----- From: "Xiao-Feng Li" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Sunday, April 29, 2007 8:36 PM Subject: Re: problem about System.loadLibrary and object's address
> On 4/29/07, LvJimmy，Jing <[EMAIL PROTECTED]> wrote: >> 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. :) > > 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" <[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 >> > > > -- > http://xiao-feng.blogspot.com >
