The following quick snippet crashes with GCC 4.5.0, on the second call to
get():
"""
#include <future>
int make_int() { return 52; }
int main()
{
std::future<int> future_in = std::async(make_int);
printf("%d\n", future_in.get());
printf("%d\n", future_in.get());
}
"""
Backtrace:
Program received signal SIGSEGV, Segmentation fault.
0x0000000000401c3f in std::__future_base::_State::wait (this=0x0) at
/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.0/include/g++-v4/future:281
281 _M_run_deferred();
(gdb) backtrace
#0 0x0000000000401c3f in std::__future_base::_State::wait (this=0x0) at
/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.0/include/g++-v4/future:281
#1 0x0000000000402e9d in std::__basic_future<int>::_M_get_result
(this=0x7fffffffd880)
at /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.0/include/g++-v4/future:515
#2 0x0000000000402560 in std::future<int>::get (this=0x7fffffffd880) at
/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.0/include/g++-v4/future:594
#3 0x00000000004017a2 in main () at promise.cpp:10
Obviously this is not a valid operation, since get() moves the result and then
zaps itself (and valid() returns false after get() is called). However from a
usability standpoint this doesn't seem ideal. It looks like adding a check in
__basic_future::_M_get_result that ensures that _M_state is not NULL would be
sufficient to catch this case.
I would assume the result of doing a get() when !valid() is undefined, so
throwing an exception when someone does this would be conforming, and a lot
more obvious and friendly. If for some reason this couldn't work, even just an
assertion fail would be more informative than a NULL pointer deref.
--
Summary: [c++0x] std::future will crash with NULL deref if get()
is called twice
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: lloyd at randombit dot net
GCC build triplet: x86_64-pc-linux-gnu
GCC host triplet: x86_64-pc-linux-gnu
GCC target triplet: x86_64-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45133
