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.

Using a UncaughtExceptionHandler is no option either, because I only have the binaries of the programs that is executed.

Can anyone help me?

EDIT: It is important that the technique is available through a command line or similar, because I need to automated this. Using a GUI is no option

Answer 1

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.