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problem with ocamlmktop -output-obj
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Date: | 1998-11-03 (15:59) |
From: | Pascal Brisset <pascal.brisset@c...> |
Subject: | Re: problem with ocamlmktop (contd) |
Pascal Brisset writes: > (3) catching a C++ exception generated by a C++ primitive called > through a Caml callback. Oops, I shouldn't have included the last part... Here is a tentative list of issues regarding exceptions and Caml/C++ interfacing. I hope others will contribute; this is definitely tricky. * g++-2.8.1 seems to link C/C++ reliably, therefore nesting Caml/C++ and C++/Caml calls without exceptions on either side should be safe. * C++ primitive raising a Caml exception: The following code is incorrect because mlraise uses siglongjmp, which does not unwind the C++ stack (obj will not be destroyed): | extern "C" value caml_stub(value) { | Object obj(...); | mlraise(...); | } This might be safe for practical purposes: | extern "C" value caml_stub(value) { | try { /* pure C++ stuff */; } | catch (...) { failwith("Uncaught C++ exception"); } | } but only a C++ expert could tell whether the exception's destructor (if any) will be called... * Callback raising a Caml exception: This is unsafe for the same reason: | extern "C" value caml_stub(value) { | Object obj(...); | callback(...); | } * C++ primitive throwing a C++ exception: We might want to have the interpreter translate all C++ exceptions into Caml exceptions: | Instruct(C_CALL1): | Setup_for_c_call; | try { accu = cprim[*pc](accu); } | catch (...) { | local_roots = initial_local_roots; | failwith("Uncaught C++ exception"); | } | Restore_after_c_call; | ... The local_roots assignment is meant to handle exceptions thrown from within a Begin_roots/End_roots block (i.e. don't let failwith() allocate memory while local_roots points to an obsolete stack frame). Is this enough ? * Caml callback throwing a C++ exception (i.e. trying to embed Caml code in C++ code transparently like in my example): I believe similar changes are required in order to return from interprete() gracefully (catch the C++ exception, handle things like external_raise, callback_depth and local_roots, then re-throw the exception). Has anyone done this ? - Pascal Brisset <pascal.brisset@cnet.francetelecom.fr> +33296051928 - - France Telecom CNET DTL/MSV | 2 av Pierre Marzin | F-22307 Lannion -