handling signals in native code - with JVM crash with SIGSEGV in terminal

Question

this is my first post so please show some understanding. I have some java code and I have some native code.

The java part isn't so interesting at the moment so I'll skip to the c++ part:

//some more trivial includes
#include <signal.h>


//these are global variables
jclass GLOBAL_CLASS;
JNIEnv * GLOBAL_ENV;
jobject GLOBAL_OBJECT;
jmethodID METHOD_ID;

void sigproc(int signo)
{
    if (signo == SIGINT)
{
        signal(SIGINT, sigproc);
        //if Ctrl-c is pressed I want to call a method within my java class
        //since I can pass only int to this function
        //I've decided to use global variables
        GLOBAL_ENV->CallVoidMethod(GLOBAL_OBJECT, METHOD_ID);
        exit(0);
    }
}

JNIEXPORT void JNICALL Java_intern_Work_readFromFile
(JNIEnv *env, jobject obj, jobjectArray arr)
{

/*define a signal trap! */
signal(SIGINT, sigproc);
//sigproc(SIGINT);
/*initialize the global variables */
GLOBAL_ENV = env;
GLOBAL_OBJECT = obj;
GLOBAL_CLASS = env->GetObjectClass(obj);
//method id is the same so it's better to cache it
//at the beginning
jmethodID mid = env->GetMethodID(GLOBAL_CLASS,
                                      "nativeListener", 
                                      "(Ljava/lang/String;)V");
METHOD_ID = GLOBAL_ENV->GetMethodID(GLOBAL_CLASS,
                    "closeEverything", "()V");
    //let's say I have a while(true) block just below
    //and some more work is done.
}

This function is triggered at the start of my MainClass. The program runs correctly if I remove

GLOBAL_ENV->CallVoidMethod(GLOBAL_OBJECT, METHOD_ID);

but the problem is that I need it because I plan to free some dynamic allocated memory + I need to call this function of my class. (in other words ... when I press ctrl-c in terminal it says JVM cheshes with SIGSEGV)

It seems I don't actually understand what really is going on when a signal is passed from the kernel. Is my global variable GLOBAL_ENV still a correct pointer that I can use?

Can anyone tell me an elegant way to solve my problem? Or any guidance is welcome, too! Any explanation ... anything at all. Thanks in advance!

Here's a sample of the JVM crash code:

A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007f9974cfc021, pid=7099, tid=140297087112960
#
# JRE version: 6.0_24-b24
# Java VM: OpenJDK 64-Bit Server VM (20.0-b12 mixed mode linux-amd64 compressed oops)
# Derivative: IcedTea6 1.11.4
# Distribution: Ubuntu 12.04 LTS, package 6b24-1.11.4-1ubuntu0.12.04.1
# Problematic frame:
# V  [libjvm.so+0x617021]  methodOopDesc::result_type() const+0x31

Answer 1

Your problem is that SIGINT is an asynchronous signal; it can occur between any two machine instructions unless blocked.

This means that it is not safe to call anything but async-safe functions from your signal handler (and, if you want to be portable, you should not do anything but set sig_atomic_t variables). The JVM most certainly does not count as async-safe. Most likely, you are interrupting the JVM in the middle of some important code, and your method call is corrupting JVM state.

The approach usually used for handling SIGINT is to have a loop somewhere which checks a flag variable (of type sig_atomic_t). When you get a SIGINT, set the flag and return. The loop will come around and execute the rest of the handler in a safe, synchronous fashion.

In your case, you can just spawn off a Java thread which periodically calls a checkForInterrupt function that checks the aforementioned flag variable. checkForInterrupt returns the current flag status, and your thread can then choose to act on it.

The other option is to use a function like pause, sigwait or sigsuspend to suspend a thread until a signal is received. The thread then wakes up and processes the signal synchronously.

Answer 2

Take a look at http://javajiggle.com/2008/01/06/if-jni-based-application-is-crashing-check-signal-handling/ Seems like it might be the issue you are describing.

Edit: That link is old, this is the information that was in it:

http://docs.oracle.com/javase/7/docs/technotes/guides/vm/signal-chaining.html

To use libjsig.so, either link it with the application that creates/embeds a HotSpot VM, for example:

cc -L -ljsig -ljvm java_application.c

or use LD_PRELOAD environment variable, for example:

export LD_PRELOAD=/libjsig.so; java_application (ksh)

setenv LD_PRELOAD /libjsig.so; java_application (csh)

The interposed signal()/sigset()/sigaction() return the saved signal handlers, not the signal handlers installed by the Java HotSpot VM which are seen by the OS.

The signal-chaining facility was introduced to address Request for Enhancement number 4381843.