Re: Threads - When?
Le Chaud Lapin wrote:
dd.foldhill@googlemail.com wrote:
How long will it be before c++ has anything to say about threads?
A Very Long Time, hopefully.
In other words, you prefer the current situation, where it is
impossible to use threads at all in portable C++. (Even on the
same system: under Solaris, code written for Sun CC does not
work with g++, and vice versa, even though both use the same
underlying Posix implementation.)
I think that it is possible to use C++ as it is effectively in a
multi-threaded environment, provided that good primitives to support
such an environment have been created. In particular, the
synchronization primitives are critical (no pun intended).
You need more than primitives. As long as accessing memory from
two different threads is undefined behavior, you cannot write
multithreaded programs. And the current sequence point model
simply doesn't work in a multithreaded environment.
[...]
To give two hints:
1. There was a post not long about where a programmer wanted to
manually rollback the stack of another thread, essentially duplicating
what exception handling code would do.
2. There is also the recurring scenario where thread B is in the middle
of a lengthy process and thread A wants it to stop right away, but in a
clean way also.
I believe that both of these problems, if solved elegantly, would force
a fundamental reconsideration of the basic principles underlying thread
usage, and a framework supporting the new model could be implemented
entirely in C++, relatively portably, with no changes to the language.
C++ has a requirement that it be implementable under current
operating systems. Under current operating systems---at least
under Solaris and Linux, and I think under Windows---there is no
way to implement a general solution to these problems; both
require significant collaboration in the manipulated thread. So
it would be extremely surprising if the C++ standard required a
solution to them. And useless---a standard that cannot be
implemented under Windows or Unix isn't of any interest to
anyone.
--
James Kanze (Gabi Software) email: james.kanze@gmail.com
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