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我对JNI看起来并没有太多运气。我正在等待我买的一本书到达，但现在它是反复试验。使用java JNI GetFieldID和JNI一般
我正在使用JNI来实现一个Lua评估器。 evaluateatorNew（）只创建一个新的Evaluator（）对象，按照Java方面的描述创建一个新的CPtr（）类对象，将我们的Evaluator（）对象的指针赋给CPtr的'peer'成员，并返回新的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;
}
这里是Java类来容纳我们的指针。这就是'env-> FindClass（）'正在调用的内容。
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() {}
}
有没有堆栈跟踪可以说，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通过上面的JNI功能步进转储：
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
这里的jni.h线708：
jfieldID GetFieldID(jclass clazz, const char* name, const char* sig)
{ return functions->GetFieldID(this, clazz, name, sig); } // 708
任何帮助吗？请让我知道是否需要澄清任何事情。
那么，事实证明，这个问题是在其他地方，由于我使用的Lua库因抛弃错误的Lua代码而抛出异常。看来，逐步通过这些JNIEnv *方法（GetFieldID）会导致虚拟机出现故障。无论如何，我从你那里学到了一些东西，所以这里是积极的。 :) – Scott 2012-04-25 03:24:47