"Julian Graham" <[EMAIL PROTECTED]> writes: > Were we to go this route (i.e., non-coexistence), I think the best > solution would be something along the lines of the divide between > Guile's built-in hash tables and SRFI-69 hash tables -- that is, > obvious incompatibility based on data type. But that seems like an > awful lot of work and a potential loss in terms of flexibility for > developers.
I agree; so overall, it seems clear that we don't want to take this route. > With regard to supporting locked/not-owned: > > >> 1. Calling lock-mutex with a thread parameter different from the >> calling thread, and which isn't #f. I believe this should be a core >> feature (as well as a SRFI-18 one), and it had completely escaped my >> notice that this detail had evaporated from your patches. I believe >> you implemented this originally, then removed it following my attempt >> to draw a line between core stuff and SRFI-18 stuff - so I guess you >> thought that was one of the implications of what I wrote; sorry about >> that. Would it be easy at this point to reinstate this? > > That was my assumption, yes. Sorry! I can certainly reinstate, and > will do so in the next patch I submit. While we're discussing this, > though, any design issues you'd like to consider? E.g., this might > not be something we'd want every mutex to support, so we could add a > flag to make-mutex, a la the earlier stuff for external unlocking. I think it depends whether we see the existing make-mutex flags as a policing thing or as a trying-to-be-helpful-at-runtime thing. My view is that they are mostly trying to be helpful, specifically to catch the bugs where a developer who is expecting traditional mutex behaviour accidentally calls unlock-mutex from the wrong thread, or on a mutex that isn't locked. In addition, there is the possibility that some existing code might be relying on exceptions being raised in these cases. The (lock-mutex ... thread) case feels to me to be quite different from this, because the (lock-mutex ...) call that a developer has to write, in order to take advantage of the SRFI-18 features, is different at the source code level: to get the SRFI-18 behaviour, the developer has to explicitly supply the optional thread parameter. This makes it impossible (or as near impossible as we care about) that a developer would get the SRFI-18 behaviour by mistake; and existing code (which cannot specify the thread parameter, because it isn't supported yet!) will automatically continue to get the traditional behaviour. Therefore I don't see the same kind of need for a make-mutex flag here, as there was for the unlock cases. >> 2. Calling lock-mutex with thread parameter #f, such as to produce the >> SRFI-18 locked/not-owned state. My previous pure Scheme suggestion >> for locked/not-owned was based on my statement that: > > ... > >> In terms of the C/Scheme boundary, one possible representation of this >> would be to introduce a mutex-locked? primitive, which is significant >> when mutex-owner returns #f, and distinguishes between the normal >> unlocked state and locked/not-owned. > > ... > >> What do you think? > > I think that's quite elegant, actually. On initial consideration I > was going to suggest that we bring back the use of SCM_UNSPECIFIED in > the context of mutex ownership (that is, fat_mutex.owner can be > SCM_UNSPECIFIED, #f, or a thread) that I'd removed in the final > version of my patch -- after all, mutex-owner is for all intents and > purposes new to the API, so we've got some freedom in how it's > defined. ...But I think I prefer the solution you describe above, > since it has the additional benefit of exposing only as much > information about mutex state as a caller is interested in. So I'll > go with that, I think, and send you a new patch for the core that > incorporates all of this. Let me know if that's not okay. Sounds good to me! Regards, Neil