vmtool command support forceGc action. #1781

arthas-vmtool/src/main/java/arthas/VmTool.java

@@ -41,6 +41,8 @@ public class VmTool implements VmToolMXBean {
      */
     private static native String check0();
 
+    private static native void forceGc0();
+
     /**
      * 获取某个class在jvm中当前所有存活实例
      */
@@ -78,6 +80,11 @@ public class VmTool implements VmToolMXBean {
         return check0();
     }
 
+    @Override
+    public void forceGc() {
+        forceGc0();
+    }
+
     @Override
     public <T> T[] getInstances(Class<T> klass) {
         return getInstances0(klass);

arthas-vmtool/src/main/java/arthas/VmToolMXBean.java

@@ -19,6 +19,11 @@ public interface VmToolMXBean {
      */
     public String check();
 
+    /**
+     * https://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#ForceGarbageCollection
+     */
+    public void forceGc();
+
     /**
      * 获取某个class在jvm中当前所有存活实例
      */

arthas-vmtool/src/main/native/include/arthas_VmTool.h

@@ -15,6 +15,14 @@ extern "C" {
 JNIEXPORT jstring JNICALL Java_arthas_VmTool_check0
   (JNIEnv *, jclass);
 
+/*
+ * Class:     arthas_VmTool
+ * Method:    forceGc0
+ * Signature: ()V
+ */
+JNIEXPORT void JNICALL Java_arthas_VmTool_forceGc0
+  (JNIEnv *, jclass);
+
 /*
  * Class:     arthas_VmTool
  * Method:    getInstances0

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

@@ -19,12 +19,6 @@ JNIEXPORT jclass JNICALL getClass(JNIEnv *env) {
     return cachedClass;
 }
 
-extern "C"
-JNIEXPORT jstring JNICALL
-Java_arthas_VmTool_check0(JNIEnv *env, jclass thisClass) {
-    return env->NewStringUTF("OK");
-}
-
 extern "C"
 jvmtiEnv *getJvmtiEnv(JNIEnv *env) {
 
@@ -36,6 +30,19 @@ jvmtiEnv *getJvmtiEnv(JNIEnv *env) {
     return jvmti;
 }
 
+extern "C"
+JNIEXPORT void JNICALL
+Java_arthas_VmTool_forceGc0(JNIEnv *env, jclass thisClass) {
+    jvmtiEnv *jvmti = getJvmtiEnv(env);
+    jvmti->ForceGarbageCollection();
+}
+
+extern "C"
+JNIEXPORT jstring JNICALL
+Java_arthas_VmTool_check0(JNIEnv *env, jclass thisClass) {
+    return env->NewStringUTF("OK");
+}
+
 extern "C"
 jobject createJavaInstance(JNIEnv *env, jclass javaClass) {
     //找到java类的构造方法

arthas-vmtool/src/test/java/arthas/VmToolTest.java

@@ -43,7 +43,7 @@ public class VmToolTest {
             System.out.println("sum size->" + vmtool.sumInstanceSize(VmTool.class));
             beforeInstances = null;
 
-            System.gc();
+            vmtool.forceGc();
             Thread.sleep(100);
             System.out.println(weakReference1.get() + " " + weakReference2.get());
             VmTool[] afterInstances = vmtool.getInstances(VmTool.class);
@@ -80,7 +80,7 @@ public class VmToolTest {
             totalTime.addAndGet(cost);
             System.out.println(i + " instance size:" + (instances == null ? 0 : instances.length) + ", cost " + cost + "ms avgCost " + totalTime.doubleValue() / i + "ms");
             instances = null;
-            System.gc();
+            vmtool.forceGc();
         }
     }
 

core/src/main/java/com/taobao/arthas/core/command/monitor200/VmToolCommand.java

@@ -46,7 +46,8 @@ import arthas.VmTool;
 @Summary("jvm tool")
 @Description(Constants.EXAMPLE
         + "  vmtool --action getInstances --className demo.MathGame\n"
-        + "  vmtool --action getInstances --className demo.MathGame --express 'instances.size()'\n"
+        + "  vmtool --action getInstances --className demo.MathGame --express 'instances.length'\n"
+        + "  vmtool --action forceGc\n"
         + Constants.WIKI + Constants.WIKI_HOME + "vmtool")
 //@formatter:on
 public class VmToolCommand extends AnnotatedCommand {
@@ -123,7 +124,7 @@ public class VmToolCommand extends AnnotatedCommand {
     }
 
     public enum VmToolAction {
-        getInstances, load
+        getInstances, forceGc, load
     }
 
     @Override
@@ -178,8 +179,14 @@ public class VmToolCommand extends AnnotatedCommand {
                     }
 
                     process.write(new ObjectView(value, this.expand).draw());
+                    process.write("\n");
                     process.end();
                 }
+            } else if (VmToolAction.forceGc.equals(action)) {
+                vmToolInstance().forceGc();
+                process.write("\n");
+                process.end();
+                return;
             }
 
             process.end();

spy/src/main/java/arthas/VmTool.java

@@ -41,6 +41,8 @@ public class VmTool implements VmToolMXBean {
      */
     private static native String check0();
 
+    private static native void forceGc0();
+
     /**
      * 获取某个class在jvm中当前所有存活实例
      */
@@ -78,6 +80,11 @@ public class VmTool implements VmToolMXBean {
         return check0();
     }
 
+    @Override
+    public void forceGc() {
+        forceGc0();
+    }
+
     @Override
     public <T> T[] getInstances(Class<T> klass) {
         return getInstances0(klass);

spy/src/main/java/arthas/VmToolMXBean.java

@@ -19,6 +19,11 @@ public interface VmToolMXBean {
      */
     public String check();
 
+    /**
+     * https://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#ForceGarbageCollection
+     */
+    public void forceGc();
+
     /**
      * 获取某个class在jvm中当前所有存活实例
      */