Subj : Re: win32 threads broken (was Win32 condition variables redux)
To   : comp.programming.threads
From : Joe Seigh
Date : Wed Aug 03 2005 01:12 pm

d|dq wrote:
> Joe,
> 
> Thanks for jumping in. I appreciate your insight.
> 
> You seem to say (even) "CV redux" can't be programmed easily using
> Win32 primitives.
> 
> Implementations I have seen rely on:
> - one or more critical sections
> - one or more semaphores
> - up to half a dozen counters
> - a data structure such as a queue or a doubly-linked linked list
> - a few Interlocked* this or Interlocked* that
> - up to a 1,000 lines of C code

Well, it can be complicated but some people may make it more
complicated than it has to be.
> 
> That's a lot of code to digest. In the end, it's very difficult to
> determine if problems are hidden in such complex implementations. (And
> I can't believe so much code and "logic" improves performance.)

That's why low level synchronization primatives are important.  If
the platform provider makes bad choices, this is what you get.
> 
> Example: The Apache Portable Runtime (APR)
> A Win32 implementation of condition variables has been part of APR for
> several years. People thought it worked. a few days ago, 2 patches had
> to be applied because it didn't work at all, even with 2 threads.

We spotted it right away since we already knew win32 condition
variables were problematic.

> 
> That's just one example. There are many others. None of them give our
> industry a good name.
> 
> But, going back to "CV redux"...
> 
> Could it be done with:
> - 1 auto-reset event object
> (using WaitForSingleObject to wait and SetEvent to communicate a
> broadcast to all waiting threads by repeatedly marking the event
> signaled)
> - 1 "broadcast" flag
> - 1 "waiting" counter
> 
> ?
No.  If there was a simple way, we'd all use that instead of
coming up with complicated solutions.

> 
> PS: According to several Microsoft employees, PulseEvent should be
> avoided like the plague. I even read that it remains in the Win32 API
> for backward compatibility reasons only.
> 
The documentation mentions that also.

-- 
Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software.

.