"Niels Möller" wrote:

If I understand the issue correctly, the question is whether or not

extern "C" { static void * cxx_alloc(size_t size) { return new char [size]; }

static void * cxx_realloc(void *p, size_t old_size, size_t new_size) { /* Left as an exercise ;-) }

static void cxx_free(void *p, size_t size) { delete [] (char *) p ; } }

...

mp_set_memory_functions(cxx_alloc, cxx_realloc, cxx_free);

will work when new raises an exception. Right?

Exactly. Here is the file ac_check_gmp_exceptions.m4 the we use for autoconfiscating the Parma Polyhedra Library:

dnl Copyright (C) 2001 Roberto Bagnara bagnara@cs.unipr.it dnl dnl This file is free software; as a special exception the author gives dnl unlimited permission to copy and/or distribute it, with or without dnl modifications, as long as this notice is preserved. dnl dnl This program is distributed in the hope that it will be useful, but dnl WITHOUT ANY WARRANTY, to the extent permitted by law; without even the dnl implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. dnl AC_DEFUN([AC_CHECK_GMP_EXCEPTIONS], [AC_CACHE_CHECK([whether GMP has been compiled with support for exceptions], ac_cv_gmp_supports_exceptions, [AC_LANG_SAVE AC_LANG_CPLUSPLUS AC_TRY_RUN([ #include <gmp.h> #include <new> #include <cstddef> #include <cstdlib>

using namespace std;

static void* x_malloc(size_t) { throw bad_alloc(); }

static void* x_realloc(void*, size_t, size_t) { throw bad_alloc(); }

static void x_free(void*, size_t) { }

int main() { mp_set_memory_functions(x_malloc, x_realloc, x_free); try { mpz_t pie; mpz_init_set_str(pie, "3141592653589793238462643383279502884", 10); } catch (bad_alloc) { exit(0); } exit(1); } ], ac_cv_gmp_supports_exceptions=yes, ac_cv_gmp_supports_exceptions=no, ac_cv_gmp_supports_exceptions=no) AC_LANG_RESTORE ]) gmp_supports_exceptions=${ac_cv_gmp_supports_exceptions} if test x"$gmp_supports_exceptions" = xyes then value=1 else value=0 fi AC_DEFINE_UNQUOTED(GMP_SUPPORTS_EXCEPTIONS, $value, [Not zero if GMP has been compiled with support for exceptions.]) ])

To me it seems a little dangerous even if -fexceptions is used and it seems to work. I don't know which gmp functions allocate temporary storage outside of the stack, which will leak when a C++ exception is raised (most function use TMP_ALLOC, which on most platforms allocates storage on the stack).

Hey, wait a minute! This is not my reading of the GMP documentation.

Custom Allocation *****************

By default, GMP uses `malloc', `realloc' and `free' for memory allocation. If `malloc' or `realloc' fails, GMP prints a message to the standard error output and terminates execution.

Some applications might want to allocate memory in other ways, or might not want a fatal error when there is no more memory available. To accomplish this, you can specify alternative memory allocation functions.

This can be done in the Berkeley compatibility library as well as the main GMP library.

...

Not only I expect all allocations that may fail to be done through the custom allocation functions; I also expect GMP not to leave inconsistent objects around in case of allocation failures. And it would also be very desirable that no memory is leaked in that cases (this is harder to achieve and can be left as a desideratum).

Can someone in the knows comment on all the issues raised here? All the best,

Roberto