JNI，如何列出所有当前实例？ [英] JNI, How to list all the current instances?

问题描述

我想知道JNI apis是否可以列出当前JVM中所有当前可用的实例（作为jobject）。

意思是：

  jvm-> AttachCurrentThreadAsDaemon（（void **）& env，0）; 
 jobject * instances; 
 int count = env-> GetInstances（& instances）; 
  

我的任务是通过它们搜索实现某个接口的对象（ env-> IsInstanceOf（）），我必须在没有类名的情况下动态和全局。

解决方案

JVMTI 会有所帮助。

1. 致电 IterateOverInstancesOfClass 标记所有必需物件;


2. 呼叫 GetObjectsWithTags 复制所有 注意 targetClass 也可以是一个接口。

     static jvmtiIterationControl JNICALL 
    HeapObjectCallback（jlong​​ class_tag，jlong​​ size，jlong​​ * tag_ptr，void * user_data）{
    * tag_ptr = 1; 
    return JVMTI_ITERATION_CONTINUE; 
   } 
    
    JNIEXPORT void JNICALL 
    Java_Test_iterateInstances（JNIEnv * env，jclass ignored，jclass targetClass）{
    JavaVM * vm; 
    env-> GetJavaVM（& vm）; 
    
    jvmtiEnv * jvmti; 
    vm-> GetEnv（（void **）& jvmti，JVMTI_VERSION_1_0）; 
    
    jvmtiCapabilities capabilities = {0}; 
    capabilities.can_tag_objects = 1; 
    jvmti-> AddCapabilities（& capabilities）; 
    
    jvmti-> IterateOverInstancesOfClass（targetClass，JVMTI_HEAP_OBJECT_EITHER，
    HeapObjectCallback，NULL）; 
    
    jlong​​ tag = 1; 
    jint count; 
    jobject * instances; 
    jvmti-> GetObjectsWithTags（1，& tag，& count，& instances，NULL）; 
    
    printf（Found％d objects with tag\\\
   ，count）; 
    
    jvmti-> Deallocate（（unsigned char *）instances）; 
   } 
     

   
   

   I would like to know if it is possible with JNI apis to list ALL the current available instances(as jobject) in the current JVM.

   Example of what I mean:

   jvm->AttachCurrentThreadAsDaemon((void**)&env,0);
   jobject* instances;
   int count = env->GetInstances(&instances);
   

   My task would be to search through them for objects which implement a certain interface(env->IsInstanceOf()), I have to do this dynamically and globally without class names

   解决方案

   JVMTI will help.

   1. Call IterateOverInstancesOfClass to tag all required objects;
   2. Call GetObjectsWithTags to copy all tagged objects to jobject* array.

   Here is an example. Note that targetClass can be also an interface.

   static jvmtiIterationControl JNICALL
   HeapObjectCallback(jlong class_tag, jlong size, jlong* tag_ptr, void* user_data) {
       *tag_ptr = 1;
       return JVMTI_ITERATION_CONTINUE;
   }
   
   JNIEXPORT void JNICALL
   Java_Test_iterateInstances(JNIEnv* env, jclass ignored, jclass targetClass) {
       JavaVM* vm;
       env->GetJavaVM(&vm);
   
       jvmtiEnv* jvmti;
       vm->GetEnv((void**)&jvmti, JVMTI_VERSION_1_0);
   
       jvmtiCapabilities capabilities = {0};
       capabilities.can_tag_objects = 1;
       jvmti->AddCapabilities(&capabilities);
   
       jvmti->IterateOverInstancesOfClass(targetClass, JVMTI_HEAP_OBJECT_EITHER,
                                          HeapObjectCallback, NULL);
   
       jlong tag = 1;
       jint count;
       jobject* instances;
       jvmti->GetObjectsWithTags(1, &tag, &count, &instances, NULL);
   
       printf("Found %d objects with tag\n", count);
   
       jvmti->Deallocate((unsigned char*)instances);
   }
   

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