Re: [boost] Boost.Threads, N2178, N2184, et al

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2007-03-19 18:48:11

On Mar 19, 2007, at 5:29 PM, Sohail Somani wrote:

> I was pretty much hoping for boost threads + cancellation.

Fwiw, this is the approach of N2184:

    http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2184.html

The very biggest change between boost::thread and N2184 is the  
addition of cancellation.  And, imho, this is a huge change.

There are several more minor changes:

*  The N2184::thread is non-copyable like boost::thread, but movable  
(taking advantage of new C++ language and std::lib features).  Movable  
N2184::thread maintains the one-to-one mapping between the std::thread  
and the OS thread which boost has (sole ownership semantics).  It just  
adds the ability to move the thread between scopes (such as return  
from factory functions).  I recently drew the analogy this way:

boost::thread is like a scoped_ptr to the OS thread.
N2184::thread is like an auto_ptr to the OS thread (the proposed  
unique_ptr would be a more accurate analogy).

*  N2184::thread separates out the concept of thread identity and  
thread handle.  In boost these are both just boost::thread.  The  
thread::id is copyable.  The only thing you can do with it is equality  
compare it.

*  N2184::thread moves some of the static boost thread members (yield,  
sleep) to a namespace called this_thread.  So the syntax for calling  
them is std::this_thread::yield() as opposed to boost::thread::yield().

*  N2184::threads adds a "back door escape hatch" to the OS thread  
called native_handle().  You can get that from the std::thread and do  
non-portable things with it at the OS level (setting thread priority  
is the poster child).

N2184 does not mention the rest of boost::threads (mutex, locks,  
condition, thread_once, TLS, etc.).  All of that stuff is pretty much  
assumed modulo details - TLS will be in the language, not the lib.   
N2184 just concentrates on the thread class (which has been much more  
controversial).

-Howard