处理内存泄漏问题，大幅度优化性能

arthas-beans/src/main/java/com/vdian/vclub/JvmUtils.java

@@ -3,8 +3,6 @@
 import com.taobao.arthas.common.AnsiLog;
 import org.scijava.nativelib.NativeLoader;
 
-import java.util.ArrayList;
-
 /**
  * @author ZhangZiCheng 2021-02-12
  * @since 3.5.1
@@ -33,7 +31,7 @@ public class JvmUtils {
     /**
      * 获取某个class在jvm中当前所有存活实例
      */
-    public static native <T> ArrayList<T> getInstances(Class<T> klass);
+    public static native <T> T[] getInstances(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
@@ -53,13 +51,12 @@ public class JvmUtils {
     /**
      * 获取所有已加载的类
      */
-    public static native ArrayList<Class<?>> getAllLoadedClasses();
+    public static native Class<?>[] getAllLoadedClasses();
 
     /**
      * 包括小类型(如int)
      */
-    @SuppressWarnings("all")
-    public static ArrayList<Class> getAllClasses() {
+    public static Class<?>[] getAllClasses() {
         return getInstances(Class.class);
     }
 

arthas-beans/src/main/native/src/jni-library.cpp

@@ -4,6 +4,21 @@
 #include <jvmti.h>
 #include "com_vdian_vclub_JvmUtils.h"
 
+//缓存
+static jclass cachedClass = nullptr;
+
+extern "C"
+JNIEXPORT jclass JNICALL getClass(JNIEnv *env) {
+    if (cachedClass == nullptr) {
+        //通过其签名找到ArrayList的Class
+        jclass theClass = env->FindClass("java/lang/Class");
+        //放入缓存
+        cachedClass = static_cast<jclass>(env->NewGlobalRef(theClass));
+        env->DeleteLocalRef(theClass);
+    }
+    return cachedClass;
+}
+
 extern "C"
 JNIEXPORT jstring JNICALL
 Java_com_vdian_vclub_JvmUtils_check(JNIEnv *env, jclass thisClass) {
@@ -21,14 +36,6 @@ jvmtiEnv *getJvmtiEnv(JNIEnv *env) {
     return jvmti;
 }
 
-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
@@ -46,7 +53,7 @@ HeapObjectCallback(jlong class_tag, jlong size, jlong *tag_ptr, void *user_data)
 }
 
 extern "C"
-JNIEXPORT jobject JNICALL
+JNIEXPORT jobjectArray JNICALL
 Java_com_vdian_vclub_JvmUtils_getInstances(JNIEnv *env, jclass thisClass, jclass klass) {
 
     jvmtiEnv *jvmti = getJvmtiEnv(env);
@@ -69,21 +76,19 @@ Java_com_vdian_vclub_JvmUtils_getInstances(JNIEnv *env, jclass thisClass, jclass
 
     jint count = 0;
     jobject *instances;
-    error = jvmti->GetObjectsWithTags(1, &tag, &count, &instances, NULL);
+    error = jvmti->GetObjectsWithTags(1, &tag, &count, &instances, nullptr);
     if (error) {
         printf("ERROR: JVMTI GetObjectsWithTags failed!%u\n", error);
         return JNI_FALSE;
     }
 
-    //通过其签名找到ArrayList的Class
-    jclass arrayListClass = env->FindClass("java/util/ArrayList");
-    jobject arrayList = createJavaInstance(env, arrayListClass);
-    jmethodID addMethod = env->GetMethodID(arrayListClass, "add", "(Ljava/lang/Object;)Z");
-    //添加元素到ArrayList实例
+    jobjectArray array = env->NewObjectArray(count, klass, nullptr);
+    //添加元素到数组
     for (int i = 0; i < count; i++) {
-        env->CallObjectMethod(arrayList, addMethod, instances[i]);
+        env->SetObjectArrayElement(array, i, instances[i]);
     }
-    return arrayList;
+    jvmti->Deallocate(reinterpret_cast<unsigned char *>(instances));
+    return array;
 }
 
 extern "C"
@@ -110,7 +115,7 @@ Java_com_vdian_vclub_JvmUtils_sumInstanceSize(JNIEnv *env, jclass thisClass, jcl
 
     jint count = 0;
     jobject *instances;
-    error = jvmti->GetObjectsWithTags(1, &tag, &count, &instances, NULL);
+    error = jvmti->GetObjectsWithTags(1, &tag, &count, &instances, nullptr);
     if (error) {
         printf("ERROR: JVMTI GetObjectsWithTags failed!%u\n", error);
         return JNI_FALSE;
@@ -122,6 +127,7 @@ Java_com_vdian_vclub_JvmUtils_sumInstanceSize(JNIEnv *env, jclass thisClass, jcl
         jvmti->GetObjectSize(instances[i], &size);
         sum = sum + size;
     }
+    jvmti->Deallocate(reinterpret_cast<unsigned char *>(instances));
     return sum;
 }
 
@@ -163,7 +169,7 @@ Java_com_vdian_vclub_JvmUtils_countInstances(JNIEnv *env, jclass thisClass, jcla
     }
 
     jint count = 0;
-    error = jvmti->GetObjectsWithTags(1, &tag, &count, NULL, NULL);
+    error = jvmti->GetObjectsWithTags(1, &tag, &count, nullptr, nullptr);
     if (error) {
         printf("ERROR: JVMTI GetObjectsWithTags failed!%u\n", error);
         return JNI_FALSE;
@@ -172,7 +178,7 @@ Java_com_vdian_vclub_JvmUtils_countInstances(JNIEnv *env, jclass thisClass, jcla
 }
 
 extern "C"
-JNIEXPORT jobject JNICALL Java_com_vdian_vclub_JvmUtils_getAllLoadedClasses
+JNIEXPORT jobjectArray JNICALL Java_com_vdian_vclub_JvmUtils_getAllLoadedClasses
         (JNIEnv *env, jclass thisClass) {
 
     jvmtiEnv *jvmti = getJvmtiEnv(env);
@@ -186,13 +192,11 @@ JNIEXPORT jobject JNICALL Java_com_vdian_vclub_JvmUtils_getAllLoadedClasses
         return JNI_FALSE;
     }
 
-    //通过其签名找到ArrayList的Class
-    jclass arrayListClass = env->FindClass("java/util/ArrayList");
-    jobject arrayList = createJavaInstance(env, arrayListClass);
-    jmethodID addMethod = env->GetMethodID(arrayListClass, "add", "(Ljava/lang/Object;)Z");
-    //添加元素到ArrayList实例
+    jobjectArray array = env->NewObjectArray(count, getClass(env), nullptr);
+    //添加元素到数组
     for (int i = 0; i < count; i++) {
-        env->CallObjectMethod(arrayList, addMethod, classes[i]);
+        env->SetObjectArrayElement(array, i, classes[i]);
     }
-    return arrayList;
+    jvmti->Deallocate(reinterpret_cast<unsigned char *>(classes));
+    return array;
 }

arthas-beans/src/test/java/com/vdian/vclub/JvmUtilsTest.java

@@ -3,8 +3,11 @@
 import org.junit.Test;
 
 import java.lang.ref.WeakReference;
-import java.util.ArrayList;
+import java.util.concurrent.atomic.AtomicLong;
 
+/**
+ * 以下测试的jvm参数均为：-Xms128m -Xmx128m
+ */
 public class JvmUtilsTest {
 
     /**
@@ -22,14 +25,14 @@ public class JvmUtilsTest {
     public void test01() {
         try {
             //调用native方法，获取已加载的类，不包括小类型(如int)
-            ArrayList<Class<?>> allLoadedClasses = JvmUtils.getAllLoadedClasses();
-            System.out.println("allLoadedClasses->" + allLoadedClasses.size());
+            Class<?>[] allLoadedClasses = JvmUtils.getAllLoadedClasses();
+            System.out.println("allLoadedClasses->" + allLoadedClasses.length);
 
             //通过下面的例子，可以看到getInstances(Class<T> klass)拿到的是当前存活的所有对象
             WeakReference<JvmUtils> weakReference1 = new WeakReference<JvmUtils>(new JvmUtils());
             WeakReference<JvmUtils> weakReference2 = new WeakReference<JvmUtils>(new JvmUtils());
             System.out.println(weakReference1.get() + " " + weakReference2.get());
-            ArrayList<JvmUtils> beforeInstances = JvmUtils.getInstances(JvmUtils.class);
+            JvmUtils[] beforeInstances = JvmUtils.getInstances(JvmUtils.class);
             System.out.println("before instances->" + beforeInstances);
             System.out.println("size->" + JvmUtils.getInstanceSize(weakReference1.get()));
             System.out.println("count->" + JvmUtils.countInstances(JvmUtils.class));
@@ -39,10 +42,98 @@ public void test01() {
             System.gc();
             Thread.sleep(100);
             System.out.println(weakReference1.get() + " " + weakReference2.get());
-            ArrayList<JvmUtils> afterInstances = JvmUtils.getInstances(JvmUtils.class);
+            JvmUtils[] afterInstances = JvmUtils.getInstances(JvmUtils.class);
             System.out.println("after instances->" + afterInstances);
         } catch (Exception e) {
             e.printStackTrace();
         }
     }
+
+    /**
+     * 没问题
+     */
+    @Test
+    public void testGetInstancesMemoryLeak() {
+        try {
+            Thread.sleep(20000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        final AtomicLong totalTime = new AtomicLong();
+        for (int i = 1; i <= 200000; i++) {
+            long start = System.currentTimeMillis();
+            WeakReference<Object[]> reference = new WeakReference<Object[]>(JvmUtils.getInstances(Object.class));
+            Object[] instances = reference.get();
+            long cost = System.currentTimeMillis() - start;
+            totalTime.addAndGet(cost);
+            System.out.println(i + " instance size:" + (instances == null ? 0 : instances.length) + ", cost " + cost + "ms avgCost " + totalTime.doubleValue() / i + "ms");
+            instances = null;
+            if (i % 100 == 0) {
+                //fixme 如果注释掉下面这行代码，被动gc，仍然会挂掉，不知道为什么
+                System.gc();
+            }
+        }
+    }
+
+    /**
+     * 没问题
+     */
+    @Test
+    public void testSumInstancesMemoryLeak() {
+        try {
+            Thread.sleep(20000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        final AtomicLong totalTime = new AtomicLong();
+        for (int i = 1; i <= 200000; i++) {
+            long start = System.currentTimeMillis();
+            long sum = JvmUtils.sumInstanceSize(Object.class);
+            long cost = System.currentTimeMillis() - start;
+            totalTime.addAndGet(cost);
+            System.out.println(i + " sum:" + sum + ", cost " + cost + "ms avgCost " + totalTime.doubleValue() / i + "ms");
+        }
+    }
+
+    /**
+     * 没问题
+     */
+    @Test
+    public void testCountInstancesMemoryLeak() {
+        try {
+            Thread.sleep(20000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        final AtomicLong totalTime = new AtomicLong();
+        for (int i = 1; i <= 200000; i++) {
+            long start = System.currentTimeMillis();
+            long count = JvmUtils.countInstances(Object.class);
+            long cost = System.currentTimeMillis() - start;
+            totalTime.addAndGet(cost);
+            System.out.println(i + " count:" + count + ", cost " + cost + "ms avgCost " + totalTime.doubleValue() / i + "ms");
+        }
+    }
+
+    /**
+     * 没问题
+     */
+    @Test
+    public void testGetAllLoadedClassesMemoryLeak() {
+        try {
+            Thread.sleep(20000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        final AtomicLong totalTime = new AtomicLong();
+        for (int i = 1; i <= 200000; i++) {
+            long start = System.currentTimeMillis();
+            Class<?>[] allLoadedClasses = JvmUtils.getAllLoadedClasses();
+            long cost = System.currentTimeMillis() - start;
+            totalTime.addAndGet(cost);
+            System.out.println(i + " class size:" + allLoadedClasses.length + ", cost " + cost + "ms avgCost " + totalTime.doubleValue() / i + "ms");
+            allLoadedClasses = null;
+        }
+    }
+
 }