Re: [asio-users] Accessing an object not from its io_service thread

[Christopher K. <ch...@ko...>]

Igor R wrote:
> Hello,
> 
> Most of asio objects (like sockets and deadline_timer) are not
> thread-safe, as stated in the documentation. However, the docs do not
> explicitly refer to the question, whether it's safe to access these
> objects from a thread, other than the one(s) that is running their
> io_serivce -- like this:
> 
> // pseudo code
> static io_service io;
> {
>   tcp::socket sock(io);
>   boost::thread(&io_service::run, &io);
>   async_write(sock, someBuffer, handler);
>   async_read(sock, someBuffer, handler);
> }
> {
>   deadline_timer timer(io);
>   timer.expires_from_this(...);
>   timer.async_wait(...);
> }

This is safe.

> In other words, does io_service change its objects' state in the way
> that might produce race condition with operations initiated by user?

No it doesn't.

The idea is that the unit of "thread safety" is the I/O object. This page:

http://www.boost.org/doc/libs/1_42_0/doc/html/boost_asio/overview/core/basics.html

shows that only operation initiation involves the thread-unsafe I/O 
object. After initiation, only the io_service is involved in the 
operation, and the io_service is a thread-safe object.

Cheers,
Chris