https://bugs.kde.org/show_bug.cgi?id=339330
Jens-W. Schicke-Uffmann <drahf...@gmx.de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |drahf...@gmx.de
--- Comment #5 from Jens-W. Schicke-Uffmann <drahf...@gmx.de> ---
This problem is not easily solved "just" by suppressions: std::atomic accesses
don't create happens-before edges, and thus spurious data races are also
reported for user code:
#include <thread>
#include <memory>
#include <atomic>
using namespace std;
int main(void) {
std::atomic<std::shared_ptr<int>> value;
thread reader([&value](){
while(true) {
auto ptr = value.load();
if(ptr && *ptr == 1) { // line 13
break;
}
}
});
value.store(make_shared<int>(1));
reader.join();
return 0;
}
compiled with g++-14 --std=c++20 -ggdb example.c++
and then valgrind --tool=helgrind a.out
reports apart from a lot of internals of std::atomic<std::shared_ptr<...>> also
==1512249== Possible data race during read of size 4 at 0x4DF0250 by thread #2
==1512249== Locks held: none
==1512249== at 0x10921E: main::{lambda()#1}::operator()() const
(example.c++:13)
==1512249== by 0x109673: void std::__invoke_impl<void,
main::{lambda()#1}>(std::__invoke_other, main::{lambda()#1}&&) (invoke.h:61)
==1512249== by 0x109636: std::__invoke_result<main::{lambda()#1}>::type
std::__invoke<main::{lambda()#1}>(main::{lambda()#1}&&) (invoke.h:96)
==1512249== by 0x1095E3: void
std::thread::_Invoker<std::tuple<main::{lambda()#1}>
>::_M_invoke<0ul>(std::_Index_tuple<0ul>) (std_thread.h:301)
==1512249== by 0x1095B7:
std::thread::_Invoker<std::tuple<main::{lambda()#1}> >::operator()()
(std_thread.h:308)
==1512249== by 0x10959B:
std::thread::_State_impl<std::thread::_Invoker<std::tuple<main::{lambda()#1}> >
>::_M_run() (std_thread.h:253)
==1512249== by 0x4964223: ??? (in
/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.33)
==1512249== by 0x484F38A: ??? (in
/usr/libexec/valgrind/vgpreload_helgrind-amd64-linux.so)
==1512249== by 0x4B9F39B: start_thread (pthread_create.c:444)
==1512249== by 0x4C2048F: clone (clone.S:100)
==1512249== Address 0x4df0250 is 16 bytes inside a block of size 24 alloc'd
==1512249== at 0x4842FD3: operator new(unsigned long) (in
/usr/libexec/valgrind/vgpreload_helgrind-amd64-linux.so)
==1512249== by 0x10A986:
std::__new_allocator<std::_Sp_counted_ptr_inplace<int, std::allocator<void>,
(__gnu_cxx::_Lock_policy)2> >::allocate(unsigned long, void const*)
(new_allocator.h:151)
==1512249== by 0x10A59B: allocate (allocator.h:196)
==1512249== by 0x10A59B: allocate (alloc_traits.h:515)
==1512249== by 0x10A59B:
std::__allocated_ptr<std::allocator<std::_Sp_counted_ptr_inplace<int,
std::allocator<void>, (__gnu_cxx::_Lock_policy)2> > >
std::__allocate_guarded<std::allocator<std::_Sp_counted_ptr_inplace<int,
std::allocator<void>, (__gnu_cxx::_Lock_policy)2> >
>(std::allocator<std::_Sp_counted_ptr_inplace<int, std::allocator<void>,
(__gnu_cxx::_Lock_policy)2> >&) (allocated_ptr.h:98)
==1512249== by 0x10A3FB:
std::__shared_count<(__gnu_cxx::_Lock_policy)2>::__shared_count<int,
std::allocator<void>, int>(int*&,
std::_Sp_alloc_shared_tag<std::allocator<void> >, int&&)
(shared_ptr_base.h:967)
==1512249== by 0x10A22F: std::__shared_ptr<int,
(__gnu_cxx::_Lock_policy)2>::__shared_ptr<std::allocator<void>,
int>(std::_Sp_alloc_shared_tag<std::allocator<void> >, int&&)
(shared_ptr_base.h:1713)
==1512249== by 0x109EEE:
std::shared_ptr<int>::shared_ptr<std::allocator<void>,
int>(std::_Sp_alloc_shared_tag<std::allocator<void> >, int&&)
(shared_ptr.h:463)
==1512249== by 0x109BF5: std::shared_ptr<int> std::make_shared<int,
int>(int&&) (shared_ptr.h:1008)
==1512249== by 0x1092A8: main (example.c++:19)
==1512249== Block was alloc'd by thread #1
==1512249==
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