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Fix uncaught_exceptions() not accounting for forced_unwind #337

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Merged
olk merged 1 commit into from
Jul 23, 2026
+51 −10
Merged

Fix uncaught_exceptions() not accounting for forced_unwind #337

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37 changes: 27 additions & 10 deletions include/boost/context/fiber_fcontext.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -70,7 +70,9 @@ namespace context {
namespace detail {

// manage_exception_state is a dummy struct unless we have specific support
struct manage_exception_state {};
struct manage_exception_state {
void from_forced_unwind() noexcept {}
};

} // namespace detail
} // namespace context
Expand All @@ -90,6 +92,11 @@ class manage_exception_state {
BOOST_NOINLINE manage_exception_state() {
exception_state_ = *__cxa_get_globals();
}
// Hack to account for the forced_unwind exception thrown in fiber_unwind
// that's run ontop before the destructor.
void from_forced_unwind() noexcept {
exception_state_.uncaughtExceptions += 1;
}
BOOST_NOINLINE ~manage_exception_state() {
*__cxa_get_globals() = exception_state_;
}
Expand Down Expand Up @@ -376,13 +383,18 @@ class fiber {
BOOST_ASSERT( nullptr != fctx_);
detail::manage_exception_state exstate;
boost::ignore_unused(exstate);
return { detail::jump_fcontext(
try {
return { detail::jump_fcontext(
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
detail::exchange( fctx_, nullptr),
detail::exchange( fctx_, nullptr),
#else
std::exchange( fctx_, nullptr),
std::exchange( fctx_, nullptr),
#endif
nullptr).fctx };
nullptr).fctx };
} catch ( detail::forced_unwind const& ) {
exstate.from_forced_unwind();
throw;
}
}

template< typename Fn >
Expand All @@ -391,14 +403,19 @@ class fiber {
detail::manage_exception_state exstate;
boost::ignore_unused(exstate);
auto p = std::forward< Fn >( fn);
return { detail::ontop_fcontext(
try {
return { detail::ontop_fcontext(
#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
detail::exchange( fctx_, nullptr),
detail::exchange( fctx_, nullptr),
#else
std::exchange( fctx_, nullptr),
std::exchange( fctx_, nullptr),
#endif
& p,
detail::fiber_ontop< fiber, decltype(p) >).fctx };
& p,
detail::fiber_ontop< fiber, decltype(p) >).fctx };
} catch ( detail::forced_unwind const& ) {
exstate.from_forced_unwind();
Comment on lines +407 to +416

@xokdvium xokdvium Jul 21, 2026

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I guess if an exception is thrown on the switched-to context it would also need to be handled here - and that's probably in-scope. Happy to tackle this (maybe in a follow-up), but I've started by putting out the immediate fire under our feet in nix.

throw;
}
}

explicit operator bool() const noexcept {
Expand Down
24 changes: 24 additions & 0 deletions test/test_fiber.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -510,6 +510,29 @@ void test_badcatch() {
#endif
}

void test_uncaught_exceptions() {
int i = 42;
{
ctx::fiber f{
[&i](ctx::fiber && f ) {
struct scope_test {
int &i_;
scope_test( int &i) :
i_(i) {
}
~scope_test() {
i_ = std::uncaught_exceptions();
}
};
scope_test scope( i);
return std::move( f).resume();
i = 84;
}};
f = std::move(f).resume();
}
BOOST_CHECK_EQUAL( i, 1);
}

int main()
{
test_move();
Expand All @@ -529,6 +552,7 @@ int main()
#endif
test_goodcatch();
test_badcatch();
test_uncaught_exceptions();

return boost::report_errors();
}
Expand Down
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