Boost.Asio SSL thread safety

Question

Do I create one strand that all of my SSL sockets share, or one strand per SSL context (shared by any associated sockets)?

Boost.Asio SSL documentation stat

Answer 1

I'd say it depends on how your protocol is like. If it's HTTP, there's no need to use an (explicit) strand as you don't read and write to your socket in parallel.

In fact, what would cause problems, is code like this:

void func()
{
    async_write(...);
    async_read(...);
}

because here -if your io_service() has a POOL of threads associated with it-, actual read and write could be carried out in parallel by several threads.

If you only have one thread per io_service, no need for a strand. The same is true if you're implementing HTTP for example. In HTTP, you don't read and write to the socket in parallel, due to the layout of the protocol. You read a request from the client -though this might be done in several async calls-, then you somehow process request and headers, then you (async or not) send your reply.

Pretty much the same you can also read in ASIO's strand documentation.