Hi, I am writing an application that creates a callback in lisp (cffi:defcallback callback-lisp ...), and then passes the pointer to a C library with something like (set-callback-in-c (cffi:callback callback-lisp). In C, I assign the function pointer as follows: /* global variable */ void (*callback)(void); void set_callback_in_c(void (*callback_from_lisp)(void)) { callback = callback_from_lisp; } And call (*callback)()); as needed. Now, everything works nicely, unless I use threads in C (pthreads). With threads, the first time I call (*callback)()); it segfaults, as if the pointer to the function was not valid (it does get assigned). I have no clue of what is going on, since it seems that the threads are not sharing the information to the function pointer. What I am missing here? I have tried with both Allegro and SBCL, on a Debian "testing". Thanks!