[Bordeaux-threads-devel] Clarifying some behavior in the documentation

[Vladimir Sedach]

>> 1. At least one implementation (SBCL) requires that the lock on which
>> condition-wait is called is to be held by the thread that calls
>> condition-notify on the corresponding CV. This should be mentioned in
>> the documentation as a requirement.
>
> Yes, this is a standard, but ill-documented, requirement for condition
> variables.  The lock is needed to synchronize the notify with the change to
> the underlying data in the application.

At least on Clozure, B-T implements condition-wait/notify with
semaphores, so this appears to work fine, even though on other
implementations it might lead to race conditions.

> I think release-lock can be allowed inside with-lock-held, as long as you call
> acquire-lock before exiting the body.

Good point. There's a lot of variation of this in the implementations
- for some implementations B-T uses the with-lock-held equivalent
provided by the implementation, which might have different semantics,
and in other implementations (like SBCL) all locks are recursive, so
it's harder to track down lock/unlock mismatch errors.

Now that I think about it some more it might be a good idea to not
just specify more semantics in the documentation, but provide
assertions for the specified behavior. It would be nice to do this
based on optimize declaration safety level. Does anyone know of a
library that provides access to declarations at macro-expansion time
like CLtL2's Environments
(http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node102.html)?

Vladimir