JNI--JNI ERROR (app bug): accessed stale local reference

最近，在APP测试过程中发现一个crash，查看log发现如下错误：

07-30 14:15:24.053: E/dalvikvm(23567): JNI ERROR (app bug): accessed stalelocal reference 0x2bf00005 (index 1 in a table of size 0)

07-30 14:15:24.053: E/dalvikvm(23567): VM aborting

仔细检查JNI层代码，没有发现什么问题，百思不得其解，最后，在网络上发现了如下解释：

Since android 4.0 garbage collector was changed. Now it moves object around during garbage collection, which can cause a lot of problems.

Imagine that you have a static variable pointing to an object, and then this object gets moved by gc. Since android uses direct pointers for java objects, this would mean that your static variable is now pointing to a random address in the memory, unoccupied by any object or occupied by an object of different sort. This will almost guarantee that you'll get EXC_BAD_ACCESS next time you use this variable.

So android gives you JNI ERROR (app bug) error to prevent you from getting undebugable EXC_BAD_ACCESS. Now there are two ways to avoid this error.

1. You can set targetSdkVersion in your manifest to version 11 or less. This will enable JNI bug compatibility mode and prevent any problems altogether. This is the reason why your old examples are working.

2. You can avoid using static variables pointing to java objects or make jobject references global before storing them by calling env->NewGlobalRef(ref).
   Perhaps on of the biggest examples here is keeping jclass objects. Normally, you'll initialize static jclass variable during JNI_OnLoad, since class objects remain in the memory as long as the application is running.

This code will lead to a crash:

 
  
static jclass myClass;
JNIEXPORT jint JNICALL JNI_OnLoad (JavaVM * vm, void * reserved) {  
    myClass = env->FindClass("com/example/company/MyClass");  
    return JNI_VERSION_1_6;  
}
 
  
 
  
 While this code will run fine:
 
  
 
  
static jclass myClass;
JNIEXPORT jint JNICALL JNI_OnLoad (JavaVM * vm, void * reserved) {  
    jclass tmp = env->FindClass("com/example/company/MyClass");  
    myClass = (jclass)env->NewGlobalRef(tmp);
    return JNI_VERSION_1_6;  
}
 
  
 
  
 通过测试，确实是这个原因，按照红色字体的解决方法，顺利解决！于是，给大家分享一下！