pthreads SIGEV_THREAD and async-safe function calls

Question

Having trouble tracking down answer to usage of SIGEV_THREAD...

When one sets SIGEV_THREAD as the notify method in sigevent struct, is it correct to assume that async-signal-safe functions must still be used within the notify_function to be invoked as the handler?

Also - is it correct to assume the thread is run as "detached"?

For example

notify thread

void my_thread(union sigval my_data)
{
    // is this ok or not (two non async-signal-safe functions)?
    printf("in the notify function\n");
    mq_send();
}

main function

(...)
se.sigev_notify = SIGEV_THREAD;
se.sigev_value.sival_ptr = &my_data;
se.sigev_notify_function = my_thread;
se.sigev_notify_attributes = NULL;
(...)

Please provide a reference if possible.

Answer 1

No, you don't need to use only async-signal-safe functions, because POSIX does not place any such limitation on the SIGEV_THREAD function. (The whole point of SIGEV_THREAD is that it lets you handle asychronous notifications in a less constrained environment than a signal handler).

As far as the thread being detached, POSIX says:

The function shall be executed in an environment as if it were the start_routine for a newly created thread with thread attributes specified by sigev_notify_attributes. If sigev_notify_attributes is NULL, the behavior shall be as if the thread were created with the detachstate attribute set to PTHREAD_CREATE_DETACHED. Supplying an attributes structure with a detachstate attribute of PTHREAD_CREATE_JOINABLE results in undefined behavior. The signal mask of this thread is implementation-defined.

This means: you must either leave sigev_notify_attributes as NULL, or set it to an attributes structure with the detachstate set to PTHREAD_CREATE_DETACHED - in both cases the thread will be created detached.