我正在使用 JVMTI 为 Java 应用程序编写一个检测工具。我已经看到 JVMTI 检测何时抛出异常以及何时捕获异常http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html#Exception http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html#Exception。
本文档规定了 Exception 和 ExceptionCatch 这两个事件
异常字段标识抛出的异常对象。
尽管它没有指示如何在运行期间比较它们(即比较 Exception 中提供的异常对应于 ExceptionCatch 中捕获的异常)。换句话说,对于
# java -version
java version "1.7.0_85"
OpenJDK Runtime Environment (IcedTea 2.6.1) (7u85-2.6.1-5ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.85-b03, mixed mode)
直接比较 jException/jobject 时,它似乎并不总是正确的。考虑监视 Exception 和 ExceptionCatch 事件的 JVMTI 代理(下面的源代码),还考虑随后引发异常的 Java 简单示例(也包括源代码),最后您可以通过“make run”使用代理运行该示例" 与给定的 Makefile(包含在最后)。
如果我使用 OpenJDK 7 运行该示例,它将给出以下结果:
# make run
...
cb_Exception (exception=0x2ae6b8087be8)
cb_ExceptionCatch (exception=0x2ae6b80859f8 vs last_exception=0x2ae6b8087be8)
AreSameObject? = 0
cb_Exception (exception=0x2ae6b80859f8)
cb_ExceptionCatch (exception=0x2ae6b807a388 vs last_exception=0x2ae6b80859f8)
AreSameObject? = 0
cb_Exception (exception=0x2ae6b807a388)
cb_ExceptionCatch (exception=0x2ae6b807a388 vs last_exception=0x2ae6b807a388)
AreSameObject? = 1
cb_Exception (exception=0x2ae6b807a388)
cb_ExceptionCatch (exception=0x2ae6b8078108 vs last_exception=0x2ae6b807a388)
AreSameObject? = 0
cb_Exception (exception=0x2ae6b8078108)
cb_ExceptionCatch (exception=0x2ae6b8078108 vs last_exception=0x2ae6b8078108)
AreSameObject? = 1
cb_Exception (exception=0x2ae6b8078108)
cb_ExceptionCatch (exception=0x2ae6b8078108 vs last_exception=0x2ae6b8078108)
AreSameObject? = 1
before doing work
cb_Exception (exception=0x2ae6b8078108)
cb_ExceptionCatch (exception=0x2ae6b8078108 vs last_exception=0x2ae6b8078108)
AreSameObject? = 1
after doing work
如果我使用 IBM 的 Java 1.7.0 运行该示例,情况有些类似。
# make run
...
cb_Exception (exception=0x7d78a0)
cb_ExceptionCatch (exception=0x7d7950 vs last_exception=0x7d78a0)
AreSameObject? = 1
cb_Exception (exception=0x7d7938)
cb_ExceptionCatch (exception=0x7d7950 vs last_exception=0x7d7938)
AreSameObject? = 0
cb_Exception (exception=0x7d7938)
cb_ExceptionCatch (exception=0x7d79a8 vs last_exception=0x7d7938)
AreSameObject? = 1
before doing work
cb_Exception (exception=0x7d7a60)
cb_ExceptionCatch (exception=0x7d7a98 vs last_exception=0x7d7a60)
AreSameObject? = 0
after doing work
在 OpenJDK 中,请注意每个 Exception 都有一个相应的 ExceptionCatch,但在主 Java 代码之外还有 6 个 Exception,我怀疑它们来自 Java VM 本身。请注意,每对中的异常值并不相同。在第 5 个回调调用之后,异常的值似乎变得恒定。 IBM 的 Java 中的情况有些类似,但引发的例外情况较少。作为 Chen Harel 评论中的建议,我存储了引发的异常,并通过 IsSameObject JNI 的方法与捕获的异常进行比较,但 JNI 声称异常不相同。
那么,在应用程序生命周期中是否可以通过Exception和ExceptionCatch来识别异常呢?如果是这样,通过 JVMTI 或 JNI 比较异常的正确方法是什么?
agent.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <jni.h>
#include <jvmti.h>
#define CHECK_JVMTI_ERROR(x,call) \
{ if (x != JVMTI_ERROR_NONE) { fprintf (stderr, "Error during %s in %s:%d\n", #call, __FILE__, __LINE__); } }
/* Global static data */
static jvmtiEnv *jvmti;
static jrawMonitorID ExtraeJ_AgentLock;
jobject last_exception;
static void JNICALL cb_Exception (jvmtiEnv *jvmti_env, JNIEnv* jni_env,
jthread thread, jmethodID method, jlocation location, jobject exception,
jmethodID catch_method, jlocation catch_location)
{
printf ("cb_Exception (exception=%p)\n", exception);
last_exception = exception;
}
static void JNICALL cb_ExceptionCatch (jvmtiEnv *jvmti_env,
JNIEnv* jni_env, jthread thread, jmethodID method, jlocation location,
jobject exception)
{
printf ("cb_ExceptionCatch (exception=%p vs last_exception=%p)\n"
"AreSameObject? = %d\n",
exception,
last_exception,
(*jni_env)->IsSameObject(jni_env, exception, last_exception));
}
JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *vm, char *options, void *reserved)
{
jint rc;
jvmtiError r;
jvmtiCapabilities capabilities;
jvmtiEventCallbacks callbacks;
/* Get JVMTI environment */
rc = (*vm)->GetEnv(vm, (void **)&jvmti, JVMTI_VERSION);
if (rc != JNI_OK)
{
fprintf (stderr, "Error!: Unable to create jvmtiEnv, rc=%d\n", rc);
return -1;
}
/* Get/Add JVMTI capabilities */
memset(&capabilities, 0, sizeof(capabilities));
capabilities.can_generate_exception_events = 1;
r = (*jvmti)->AddCapabilities(jvmti, &capabilities);
CHECK_JVMTI_ERROR(r, AddCapabilities);
/* Set callbacks and enable event notifications */
memset(&callbacks, 0, sizeof(callbacks));
callbacks.Exception = &cb_Exception;
callbacks.ExceptionCatch = &cb_ExceptionCatch;
r = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks));
CHECK_JVMTI_ERROR(r, SetEventCallbacks);
/* Exception events */
r = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
JVMTI_EVENT_EXCEPTION, NULL);
CHECK_JVMTI_ERROR(r, SetEventNotificationMode);
r = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
JVMTI_EVENT_EXCEPTION_CATCH, NULL);
CHECK_JVMTI_ERROR(r, SetEventNotificationMode);
return 0;
}
JNIEXPORT void JNICALL Agent_OnUnload(JavaVM *vm)
{
}
示例.java
public class example
{
void except () throws Exception
{ throw new Exception ("new-exception"); }
void do_work()
{
System.out.println ("before doing work");
try
{ except(); }
catch (Exception e)
{}
System.out.println ("after doing work");
}
public static void main (String [] args)
{
example e = new example();
e.do_work ();
}
}
Makefile
JAVA_JDK=/usr/lib/jvm/java-7-openjdk-amd64
all: libagent.so example.class
libagent.so: agent.c
gcc -shared -fPIC -DPIC agent.c -o libagent.so -I$(JAVA_JDK)/include
example.class: example.java
javac example.java
run: libagent.so example.class
java -agentpath:$(PWD)/libagent.so example
11月9日更新
我已经按照 Chen Harel 的建议创建了对该异常的全局引用。修改后的agent.c版本如下,执行输出如下所示。
agent.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <jni.h>
#include <jvmti.h>
#define CHECK_JVMTI_ERROR(x,call) \
{ if (x != JVMTI_ERROR_NONE) { fprintf (stderr, "Error during %s in %s:%d\n", #call, __FILE__, __LINE__); } }
/* Global static data */
static jvmtiEnv *jvmti;
static jrawMonitorID ExtraeJ_AgentLock;
jobject last_exception;
static void JNICALL cb_Exception (jvmtiEnv *jvmti_env, JNIEnv* jni_env,
jthread thread, jmethodID method, jlocation location, jobject exception,
jmethodID catch_method, jlocation catch_location)
{
printf ("cb_Exception (exception=%p)\n", exception);
last_exception = (*jni_env)->NewGlobalRef (jni_env, exception);
}
static void JNICALL cb_ExceptionCatch (jvmtiEnv *jvmti_env,
JNIEnv* jni_env, jthread thread, jmethodID method, jlocation location,
jobject exception)
{
printf ("cb_ExceptionCatch (exception=%p vs last_exception=%p)\n"
"AreSameObject? = %d\n",
exception,
last_exception,
(*jni_env)->IsSameObject(jni_env, exception, last_exception));
(*jni_env)->DeleteGlobalRef(jni_env, last_exception);
}
JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *vm, char *options, void *reserved)
{
jint rc;
jvmtiError r;
jvmtiCapabilities capabilities;
jvmtiEventCallbacks callbacks;
/* Get JVMTI environment */
rc = (*vm)->GetEnv(vm, (void **)&jvmti, JVMTI_VERSION);
if (rc != JNI_OK)
{
fprintf (stderr, "Error!: Unable to create jvmtiEnv, rc=%d\n", rc);
return -1;
}
/* Get/Add JVMTI capabilities */
memset(&capabilities, 0, sizeof(capabilities));
capabilities.can_generate_exception_events = 1;
r = (*jvmti)->AddCapabilities(jvmti, &capabilities);
CHECK_JVMTI_ERROR(r, AddCapabilities);
/* Set callbacks and enable event notifications */
memset(&callbacks, 0, sizeof(callbacks));
callbacks.Exception = &cb_Exception;
callbacks.ExceptionCatch = &cb_ExceptionCatch;
r = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks));
CHECK_JVMTI_ERROR(r, SetEventCallbacks);
/* Exception events */
r = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
JVMTI_EVENT_EXCEPTION, NULL);
CHECK_JVMTI_ERROR(r, SetEventNotificationMode);
r = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
JVMTI_EVENT_EXCEPTION_CATCH, NULL);
CHECK_JVMTI_ERROR(r, SetEventNotificationMode);
return 0;
}
JNIEXPORT void JNICALL Agent_OnUnload(JavaVM *vm)
{
}
** make run 的输出 **
# make run
...
cb_Exception (exception=0x2b13b0087c18)
cb_ExceptionCatch (exception=0x2b13b0085a08 vs last_exception=0x2b13e4001608)
AreSameObject? = 0
cb_Exception (exception=0x2b13b0085a08)
cb_ExceptionCatch (exception=0x2b13b007a388 vs last_exception=0x2b13e4001610)
AreSameObject? = 0
cb_Exception (exception=0x2b13b007a388)
cb_ExceptionCatch (exception=0x2b13b007a388 vs last_exception=0x2b13e4001618)
AreSameObject? = 1
cb_Exception (exception=0x2b13b007a388)
cb_ExceptionCatch (exception=0x2b13b0078108 vs last_exception=0x2b13b0085a00)
AreSameObject? = 0
cb_Exception (exception=0x2b13b0078108)
cb_ExceptionCatch (exception=0x2b13b0078108 vs last_exception=0x2b13b0085a08)
AreSameObject? = 1
cb_Exception (exception=0x2b13b0078108)
cb_ExceptionCatch (exception=0x2b13b0078108 vs last_exception=0x2b13b0085a10)
AreSameObject? = 1
before doing work
cb_Exception (exception=0x2b13b0078108)
cb_ExceptionCatch (exception=0x2b13b0078108 vs last_exception=0x2b13b0085a18)
AreSameObject? = 1
after doing work