[Boost-users] Re: Condition variable and const-correctness

From: Mark Sizer (boost_at_[hidden])
Date: 2003-10-22 11:26:16

Scott McCaskill wrote:

>>We both seem to agree that merely grabbing a mutex (or blocking on an
>>attempt to grab a mutex) is not changing the object's state.
>>
> You're saying acquring a mutex doesn't change its state?

It definitely changes the mutex's state. I don't think it _necessarily_ 
changes the state of the object that contains the mutex. A thread-safe 
"is the container empty?" method needs to acquire the mutex in order to 
check the container's empty-ness state, but it does not affect the 
container, itself. In a class that simply wraps a container to provide 
thread-safety, I think it can reasonably be argued that the state of the 
wrapper object is not changed. Obviously the "insert an object into the 
container" method requires the mutex lock AND changes the state of the 
container, itself. That method, IMHO, cannot be justifiably made const.

>>Somehow, and this is a gut feeling, the condition.wait() seems different
>>to me. Perhaps because it requires a change in the objects state in
>>order to continue.
>>
> In this case, I think the names of the operations are misleading as far as
> constness is concerned.  "lock" sounds a lot like something that changes
> state, but "wait" doesn't--it sounds quite passive by comparison.
> 

I agree - it sounds strange. Perhaps I'm simply wrong here. I'll need a 
better argument than naming conventions, which are notoriously 
arbitrary, to convince me though :)

- Mark