pthread_mutex and resuming/stopping_java

Hi all, we're new to sablevm and try to contribute to nizar's work.
We've lot of questions!

Why do we need these two calls in JVMDI (libsablevm/debug_interface.c)?
    _svmm_resuming_java (env);
    ...
    _svmm_stopping_java (env);
or
    _svmm_stopping_java (env);
    ...
    _svmm_resuming_java (env);

Why is sometimes the following used
    pthread_mutex_lock (&vm->global_mutex);
    ...
    pthread_mutex_unlock (&vm->global_mutex);

instead of this?
    _svmm_mutex_lock (jdwp->global_mutex);
    ...
    _svmm_mutex_unlock ();

Thanks

Martin