0
我對JNI看起來並沒有太多運氣。我正在等待我買的一本書到達，但現在它是反覆試驗。使用java JNI GetFieldID和JNI一般
我正在使用JNI來實現一個Lua評估器。 evaluateatorNew（）只創建一個新的Evaluator（）對象，按照Java方面的描述創建一個新的CPtr（）類對象，將我們的Evaluator（）對象的指針賦給CPtr的'peer'成員，並返回新的CPtr jobject。
JNIEXPORT jobject JNICALL Java_com_starlon_libscriptable_UtilsEvaluator_evaluatorNew(
JNIEnv *env, jclass clazz)
{
int foo = 1;
while(foo);
Evaluator *eval = new Evaluator();
jobject obj;
jclass tempClass;
tempClass = env->FindClass("com/starlon/libscriptable/CPtr");
obj = env->AllocObject(tempClass);
if (obj)
{
env->SetLongField(obj, env->GetFieldID(tempClass, "peer", "J"), (jlong)eval);
}
return obj;
}
這裏是Java類來容納我們的指針。這就是'env-> FindClass（）'正在調用的內容。
public class CPtr
{
/* Pointer value of the real C pointer. Use long to be 64-bit safe. */
private long peer;
protected long getPeer()
{
return peer;
}
/* No-args constructor. */
CPtr() {}
}
有沒有堆棧跟蹤可以說，你可以看到下面。
(gdb) bt
#0 0xafd15ca8 in __libc_android_abort()
from /home/scott/workspace/StarVisuals/StarVisuals/obj/local/armeabi-v7a/libc.so
#1 0x00000008 in ??()
Backtrace stopped: frame did not save the PC
下面是GDB通過上面的JNI功能步進轉儲：
0x80805258 in Java_com_starlon_libscriptable_UtilsEvaluator_evaluatorNew (env=0xabd8,
clazz=0x40715698) at jni/libscriptable//evaluator.cpp:85
85 while(foo);
Current language: auto; currently c++
(gdb) set foo = 0
(gdb) s
[New Thread 11226]
[Switching to Thread 11226]
87 Evaluator *eval = new Evaluator();
(gdb) u
92 tempClass = env->FindClass("com/starlon/libscriptable/CPtr");
(gdb) u
94 obj = env->AllocObject(tempClass);
(gdb) u
95 if (obj)
(gdb) s
97 env->SetLongField(obj, env->GetFieldID(tempClass, "peer", "J"), (jlong)eval);
(gdb) s
_JNIEnv::GetFieldID (this=0xabd8, clazz=0x40715910, name=0x8080a134 "peer", sig=0x8080a13c "J")
at /opt/android-ndk-r7b/platforms/android-9/arch-arm/usr/include/jni.h:708
708 { return functions->GetFieldID(this, clazz, name, sig); }
(gdb) print functions
$1 = (const JNINativeInterface *) 0xaca9dd68
(gdb) print this
$2 = (_JNIEnv * const) 0xabd8
(gdb) print clazz
$3 = (jclass) 0x40715910
(gdb) print name
$4 = 0x8080a134 "peer"
(gdb) print sig
$5 = 0x8080a13c "J"
(gdb) print *functions
$6 = {reserved0 = 0x0, reserved1 = 0x0, reserved2 = 0x0, reserved3 = 0x0, GetVersion = 0xaca43385,
DefineClass = 0xaca43355, FindClass = 0xaca4773d, FromReflectedMethod = 0xaca47719,
FromReflectedField = 0xaca476f5, ToReflectedMethod = 0xaca476b9, GetSuperclass = 0xaca44801,
IsAssignableFrom = 0xaca4450d, ToReflectedField = 0xaca4767d, Throw = 0xaca43331,
ThrowNew = 0xaca47655, ExceptionOccurred = 0xaca447b1, ExceptionDescribe = 0xaca4761d,
ExceptionClear = 0xaca43315, FatalError = 0xaca44d99, PushLocalFrame = 0xaca475c1,
PopLocalFrame = 0xaca47561, NewGlobalRef = 0xaca44ac1, DeleteGlobalRef = 0xaca4502d,
---Type <return> to continue, or q <return> to quit---q
SetByteFieldQuit
(gdb) print functions->GetFieldID
$7 = (jfieldID (*)(JNIEnv *, jclass, const char *, const char *)) 0xaca47435
(gdb) s
Program received signal SIGSEGV, Segmentation fault.
0xaca4cd0c in ??()
(gdb) bt
#0 0xafd15ca8 in __libc_android_abort()
from /home/scott/workspace/StarVisuals/StarVisuals/obj/local/armeabi-v7a/libc.so
#1 0x00000008 in ??()
Backtrace stopped: frame did not save the PC
(gdb) quit
這裏的jni.h線708：
jfieldID GetFieldID(jclass clazz, const char* name, const char* sig)
{ return functions->GetFieldID(this, clazz, name, sig); } // 708
任何幫助嗎？請讓我知道是否需要澄清任何事情。
那麼，事實證明，這個問題是在其他地方，由於我使用的Lua庫因拋棄錯誤的Lua代碼而拋出異常。看來，逐步通過這些JNIEnv *方法（GetFieldID）會導致虛擬機出現故障。無論如何，我從你那裏學到了一些東西，所以這裏是積極的。 :) – Scott 2012-04-25 03:24:47