Signal number = 0 in signal_set handler.

[alxn1@…]

In boost/asio/detail/impl/signal_set_service.ipp, if signal occured, but currently handlers queue is empty, signal_set_service will increment undelivered_ variable, but not save signal number. After what, if new handler will added, it will be called with zero signal number immediately, and undelivered_ decremented:

if (reg->undelivered_ > 0) {

--reg->undelivered_; io_service_.post_deferred_completion(op); return;

}

but signal number doesn't set (op->signal_number_ == 0 in this place).

I think, it's bug :)

It's can be reproduced with small test utility (in attachment): compile it, start, and post to it 10-15 SIGHUP's (kill -s SIGHUP <pid> | kill -s SIGHUP <pid> | kill -s SIGHUP <pid> | kill -s SIGHUP <pid> ...). In stdout you will see:

signal 1 received signal 1 received signal 1 received signal 1 received signal 1 received signal 1 received signal 1 received signal 1 received signal 0 received signal 1 received signal 1 received signal 1 received signal 1 received signal 0 received signal 1 received

In some cases signal number is zero.

[alxn1@…]

boost::asio::signal_set zero signal number bug.

[chris_kohlhoff]

Fixed on trunk in [85746]. Merged to release in [85838]