#include <signal.h>
#include <stdio.h>
#include <unistd.h>

/* This is initialised on startup by the Dynamite dynamic loader.  */
int (*dynamite_ckpt_ptr)(int sig, void *info, void *context) = NULL;

char ckptname[1024];

/* 
 * By default, the Dynamite checkpoint signal handler terminates the
 * process.  If you don't want the process to terminate, you must override
 * the USR1 signal and invoke the checkpoint handler directly.  
 */
void usr1handler(int sig)
{
    /* The meaning of the arguments:
     *
     * if sig == 0, it means that the checkpoint signal handler has not
     * been invoked by delivering a signal, but has been directly invoked
     * from the application, like any other function.  In that case, the
     * meaning of the other 2 parameters changes:
     *
     * info: determines if the process terminates after checkpointing (0)
     * or not (any other value).
     * context: must contain the pathname to the checkpoint file.
     * The "$DPVM_CKPTDIR/ckptFileName" file is not generated in this case.
     *
     * Moreover, unlike usual signal handler, dynamite_ckpt_ptr returns an int,
     * which is only significant for the "info != 0" case.  If it returns 0,
     * it indicates that the process was checkpointed, but not terminated.
     * If it returns 1, it means that this is a restart from the checkpoint.
     *
     * WARNING: this is all considered to be an internal interface, and is
     * subject to change without notice.
     */
    if (dynamite_ckpt_ptr(0, (void*)1, ckptname))
        fprintf(stderr,"Just restarted from checkpoint.\n");

    signal(sig, usr1handler);
}

int main(void)
{
    sprintf(ckptname, "%s/checkpointFile", getenv("DPVM_CKPTDIR"));
    signal(SIGUSR1, usr1handler);

    for (;;)
    {
        fprintf(stderr, "blah, blah\n");
        sleep(5);
    }
}