Generate Java Heap Dump on uncaught Exception

Question

I try to generate a Heap Dump when a uncaught exception is fired. I tried using jmap, but because the process is finished when the exception happens this is not possible.

Answer 1

Try to put your processing into a deamon thread. this way you can access it with memory analysis tools. JVisualVM is a JDK tool you can find it in your JAVA_HOME\bin.

There are also another way, called dump analyser. You run your application with these JVM parameters :

• -XX:+HeapDumpOnOutOfMemoryError

• -XX:HeapDumpPath="your_path"

But this is used only if you have an OutOfMemoryError. Try to find if it's possible to generate the dump for any performance.

Another good eclipse based tool is MemoryAnalyzer

Answer 2

I would like to suggest Java Visual VM. It can connect dynamically. I found it useful. You might want to give a try.

Answer 3

This can be achieved with JVMTI agent that will listen to VMDeath event and then use JMM interface to initiate Heap Dump.

Here is a sample source code of such JVMTI agent:

#include <jvmti.h>
#include <string.h>
#include <stdio.h>
#include "jmm.h"

JNIEXPORT void* JNICALL JVM_GetManagement(jint version);

void JNICALL VMDeath(jvmtiEnv* jvmti, JNIEnv* jni) {
    JmmInterface* jmm = (JmmInterface*) JVM_GetManagement(JMM_VERSION_1_0);
    if (jmm == NULL) {
        printf("Sorry, JMM is not supported\n");
    } else {
        jstring path = (*jni)->NewStringUTF(jni, "dump.hprof");
        jmm->DumpHeap0(jni, path, JNI_TRUE);
        printf("Heap dumped\n");
    }
}

JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM* vm, char* options, void* reserved) {
    jvmtiEnv* jvmti;
    (*vm)->GetEnv(vm, (void**)&jvmti, JVMTI_VERSION_1_0);

    jvmtiEventCallbacks callbacks;
    memset(&callbacks, 0, sizeof(callbacks));
    callbacks.VMDeath = VMDeath;
    (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks));
    (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, JVMTI_EVENT_VM_DEATH, NULL);

    return 0;
}

After you've compiled it into the shared library (libdump.so) run Java with -agentpath option:

java -agentpath:/path/to/libdump.so MainClass

If you wish to handle uncaught exceptions instead of waiting for VMDeath, you may use similar technique to install callback for Exception event. Look here for an example.