> From: Andy Wingo <wi...@pobox.com> >> As an aside, I can get a similar sort of deadlock during garbage >> collection of SMOBs if my smob_free function calls a scheme function. >> But the manual does note that you should not call any functions in >> SMOB GC finalizers, so that wouldn't happen if I actually followed the >> instructions. > > Any Scheme function? With Guile 2.0? It should be possible to call > arbitrary code from finalizers, if we call finalizers from a separate > thread.
Happens with any scheme function called in a SMOB's finalizer, with Guile 2.0, in a memory constrained situation. For example, Guile-ncurses has a SMOB finalizer that calls a guardian previously created with 'make-guardian'. This is in the <form> SMOB. Here's the order of operations - GC_invoke_finalizers calls the <form> SMOB's free function 'gc_form_free' - my SMOB finalizer gc_form_free calls a guardian procedure with scm_call_0 remove the guardian - That kicks off a new scm_c_vm_run then calls scm_i_smob_apply_trampoline - there is some mutex in the trampoline process - A new trampoline causes a memory allocation with scm_hash_fn_create_handle_x - Since memory is low, it calls GC_invoke_finalizers - This ends up making a call to my finalizer gc_form_free. (Don't know if this is a recursive call to my SMOB finalizer or if it is a call to a different <form>'s SMOB finalizer, since I have many forms) - the gc_form_free calls a guardian with scm_call_0 - which kicks off a new scm_c_v_run - which eventually gets you to scm_i_smob_apply_trampoline again - which leads to a recursive mutex lock in scm_i_smob_apply_trampoline -Mike
