Asio supports programs that utilise the fork() system call. Provided the program calls io_service.notify_fork() at the appropriate times, Asio will recreate any internal file descriptors (such as the "self-pipe trick" descriptor used for waking up a reactor). The notification is usually performed as follows:

io_service_.notify_fork(asio::io_service::fork_prepare);
if (fork() == 0)
{
  io_service_.notify_fork(asio::io_service::fork_child);
  ...
}
else
{
  io_service_.notify_fork(asio::io_service::fork_parent);
  ...
}

User-defined services can also be made fork-aware by overriding the io_service::service::fork_service() virtual function.

Note that any file descriptors accessible via Asio's public API (e.g. the descriptors underlying basic_socket<>, posix::stream_descriptor, etc.) are not altered during a fork. It is the program's responsibility to manage these as required.

See Also

io_service::notify_fork(), io_service::fork_event, io_service::service::fork_service(), Fork examples.