Condition variables?

[Sean Kelly]

Steven Schveighoffer wrote:
> "Sean Kelly" <sean at f4.ca> wrote in message 
> news:fdtqpn$259o$1 at digitalmars.com...
>> Steven Schveighoffer wrote:
>>> So the code above has to do something special by unlocking the object 
>>> before waiting using an atomic operation.  I think this requires some 
>>> language support.
>> Doing this efficiently typically requires OS support.  The library must 
>> indicate to the OS that a context switch may not occur while certain 
>> portions of the code are executing.  It is possible to implement condvars 
>> without OS support as well, but the implementation tends to be fairly 
>> complicated.  Look for version(Win32) blocks in the Tango implementation 
>> for one such example.
> 
> Why can't you use SignalObjectAndWait?  Are you not using Win32 Mutexes in 
> Win32?

Nope.  Critical sections.  For what it's worth, the Tango condvar 
implementation is pretty similar to the one in Boost.

> I implemented a C++ OS abstraction library, and I had no problems 
> implementing conditions on Win32 using OS support...

Frankly, I've never used SignalObjectAndWait.  I think the only place 
things may get a bit weird is in a notifyAll routine.  I guess you'd 
have to use a semaphore for the wait object and perhaps a separate 
counter to track the number of threads waiting on it?


Sean