https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103382
Bug ID: 103382
Summary: condition_variable::wait() is not cancellable because
it is marked noexcept
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: vanyacpp at gmail dot com
Target Milestone: ---
At the moment condition_variable::wait() is marked noexcept. It means that if
pthread_cond_wait() acts as cancellation point and throws an exception the
program is terminated with std::terminate(). This program demonstrates the
issue:
#include <condition_variable>
#include <thread>
int main()
{
std::mutex m;
std::condition_variable cv;
std::thread th([&]
{
std::unique_lock lock(m);
cv.wait(lock);
});
pthread_cancel(th.native_handle());
th.join();
}
This program terminates with SIGABRT.
Because of this using condition_variable::wait() in cancellable threads is
tricky: the programmer has to guard all calls to condition_variable::wait()
with disabling/restoring cancellation state. Also this stops the thread from
being cancellable while in wait(). Therefore the outer thread has to know which
condition_variable the thread waits and notify this condition_variable after
pthread_cancel(). Also one should add cancellation point pthread_testcancel()
immediately after restoring cancellation state after wait().
I believe it would be great if condition_variable::wait interacted nicer with
POSIX-cancellation. I would like to suggest removing noexcept from
condition_variable::wait(). This also matches the C++ standard very well
[thread.condition.condvar] where condition_variable::wait() is not marked as
noexcept.
