[Bug libstdc++/60658] New: std::atomic is unexpectedly not lock-free

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60658

            Bug ID: 60658
           Summary: std::atomic<T*> is unexpectedly not lock-free
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppluzhnikov at google dot com

Using current trunk (r208813):

g++ -std=c++11 atomic.cc -latomic && ./a.out
a.out: atomic.cc:20: int main(): Assertion `b.is_lock_free()' failed.

As far as I can tell, this is happening because

  std::__atomic_base<Bar*>::_M_type_size()

returns sizeof(Bar) instead of returning sizeof(Bar*).


// atomic.cc
#include <atomic>
#include <assert.h>

struct Foo {
  char buf[1];
};

struct Bar {
  char buf[100];
};


int
main ()
{
  std::atomic<Foo*> a;
  assert (a.is_lock_free());

  std::atomic<Bar*> b;
  assert (b.is_lock_free());
}


Google ref: b/13626319