diff --git a/arthas-vmtool/src/main/java/arthas/VmTool.java b/arthas-vmtool/src/main/java/arthas/VmTool.java
index aaed0dc20..16ccd0d8f 100644
--- a/arthas-vmtool/src/main/java/arthas/VmTool.java
+++ b/arthas-vmtool/src/main/java/arthas/VmTool.java
@@ -41,12 +41,12 @@ public class VmTool implements VmToolMXBean {
      */
     private static native String check0();
 
-    private static native void forceGc0();
+    private static synchronized native void forceGc0();
 
     /**
      * 获取某个class在jvm中当前所有存活实例
      */
-    private static native <T> T[] getInstances0(Class<T> klass);
+    private static synchronized native <T> T[] getInstances0(Class<T> klass);
 
     /**
      * 统计某个class在jvm中当前所有存活实例的总占用内存，单位：Byte
@@ -61,14 +61,14 @@ public class VmTool implements VmToolMXBean {
     /**
      * 统计某个class在jvm中当前所有存活实例的总个数
      */
-    private static native long countInstances0(Class<?> klass);
+    private static synchronized native long countInstances0(Class<?> klass);
 
     /**
      * 获取所有已加载的类
      * @param klass 这个参数必须是 Class.class
      * @return
      */
-    private static native Class<?>[] getAllLoadedClasses0(Class<?> klass);
+    private static synchronized native Class<?>[] getAllLoadedClasses0(Class<?> klass);
 
     @Override
     public String check() {
diff --git a/arthas-vmtool/src/main/native/src/jni-library.cpp b/arthas-vmtool/src/main/native/src/jni-library.cpp
index a953dce29..6f9002f2a 100644
--- a/arthas-vmtool/src/main/native/src/jni-library.cpp
+++ b/arthas-vmtool/src/main/native/src/jni-library.cpp
@@ -6,6 +6,7 @@
 
 
 static jvmtiEnv *jvmti;
+static jlong tagCounter = 0;
 
 extern "C"
 int init_agent(JavaVM *vm, void *reserved) {
@@ -57,19 +58,8 @@ Java_arthas_VmTool_check0(JNIEnv *env, jclass thisClass) {
 }
 
 extern "C"
-jobject createJavaInstance(JNIEnv *env, jclass javaClass) {
-    //找到java类的构造方法
-    jmethodID construct = env->GetMethodID(javaClass, "<init>", "()V");
-    //生成java类实例
-    return env->NewObject(javaClass, construct, "");
-}
-
-extern "C"
-jlong getClassHashCode(JNIEnv *env, jclass javaClass) {
-    //找到java类的hashCode方法
-    jmethodID hashCodeMethod = env->GetMethodID(javaClass, "hashCode", "()I");
-    //生成java类实例
-    return env->CallLongMethod(javaClass, hashCodeMethod);
+jlong getTag() {
+    return ++tagCounter;
 }
 
 extern "C"
@@ -83,8 +73,7 @@ HeapObjectCallback(jlong class_tag, jlong size, jlong *tag_ptr, void *user_data)
 extern "C"
 JNIEXPORT jobjectArray JNICALL
 Java_arthas_VmTool_getInstances0(JNIEnv *env, jclass thisClass, jclass klass) {
-    //这里用hashCode作为标记
-    jlong tag = getClassHashCode(env, klass);
+    jlong tag = getTag();
     jvmtiError error = jvmti->IterateOverInstancesOfClass(klass, JVMTI_HEAP_OBJECT_EITHER,
                                                HeapObjectCallback, &tag);
     if (error) {
@@ -112,8 +101,7 @@ Java_arthas_VmTool_getInstances0(JNIEnv *env, jclass thisClass, jclass klass) {
 extern "C"
 JNIEXPORT jlong JNICALL
 Java_arthas_VmTool_sumInstanceSize0(JNIEnv *env, jclass thisClass, jclass klass) {
-    //这里用hashCode作为标记
-    jlong tag = getClassHashCode(env, klass);
+    jlong tag = getTag();
     jvmtiError error = jvmti->IterateOverInstancesOfClass(klass, JVMTI_HEAP_OBJECT_EITHER,
                                                HeapObjectCallback, &tag);
     if (error) {
@@ -154,8 +142,7 @@ JNIEXPORT jlong JNICALL Java_arthas_VmTool_getInstanceSize0
 extern "C"
 JNIEXPORT jlong JNICALL
 Java_arthas_VmTool_countInstances0(JNIEnv *env, jclass thisClass, jclass klass) {
-    //这里用hashCode作为标记
-    jlong tag = getClassHashCode(env, klass);
+    jlong tag = getTag();
     jvmtiError error = jvmti->IterateOverInstancesOfClass(klass, JVMTI_HEAP_OBJECT_EITHER,
                                                HeapObjectCallback, &tag);
     if (error) {