https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111676
Bug ID: 111676
Summary: Race condition in std::ios::Init
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
#include <ios>
#include <thread>
void f() { std::ios::Init i; }
int main()
{
std::thread t1(f);
std::thread t2(f);
t1.join();
t2.join();
}
A possible execution for this program is:
t1 runs the Init constructor which increments Init::_S_refcount to 1 and
performs the one-time initialization of the global streams.
t2 runs the Init constructor and increments the refcount to 2.
t2 runs the ~Init destructor, which decrements the refcount to 1 and so flushes
the global streams (while still under construction).
t1 finishes constructing the global streams, and increments _S_refcount to 2.
t1 runs the ~Init destructor, which decrements the refcount to 1 and so flushes
the global streams again.
Flushing twice isn't a problem, but t2 should block until t1 finishes
constructing them, so that it doesn't flush objects that haven't finished
initialization yet.
We could just use a local static so that the __cxa_guard routines are used to
make the second thread block until the initialization is complete.
