Michael Glassford wrote:
To address these problems, I would like to redefine the lock concept constructors as follows (changes indicated with "^"):
Definitions ----------- L: lock type l: lock variable (type L) m: mutex variable (appropriate Mutex type) s: initial lock state (enum type {NO_LOCK=0, LOCK=1}) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ b: block? (enum type blocking_state {NON_BLOCKING=0, BLOCKING=1}) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Lock Concept ------------ L l(m,s) //Blocking lock if s L l(m) //Blocking lock
TryLock Concept --------------- L l(m,s,b) //Lock if s; blocking if b ^ ^^^^^^^^^^^^^ L l(m,b) //Lock; blocking if b ^ ^^^^^^^^^^^^^
TimedLock Concept ----------------- L l(m,s,b) //Lock if s; blocking if b ^ ^^^^^^^^^^^^^ L l(m,t) //Blocking lock, failing if not obtained by time t
I like this proposal, if for no other reason than the move to enums makes the arguments clearer. A couple of points: TryLock: What would be the semantics of l(m, NO_LOCK, b)? In other words, if you're not going to lock on construction, why specify a blocking policy? L l(m, b) and L l(m, s) seem to cover the two scenarios: either I don't want to lock, or I do and I need to specify the blocking policy. TimedLock: I'm not sure I follow the reasons why TimedMutex refines TryMutex. (This is a comment on the original design, not your specific changed, but bear with me.) I think a timeout of zero seconds achieves the same goal, even if TimedLock/TimedMutex don't implement the same operations. So I don't think that TimedLock needs a constructor that takes a blocking argument, and ultimately I think TimedLock/TimedMutex should refine Mutex/Lock, and not TryMutex/TryLock. Also, the current implementation of TimedLock doesn't support a single argument constructor, even though it is supposedly a refinement of TryLock, which does. I'd like to see TimedLock implemented in such a way that I could use it as if it were a simple Lock, which I currently cannot. In summary, this is what I'd like to see: Lock Concept --------------- L l(m) //Blocking lock L l(m,s) //Blocking lock if s TryLock Concept --------------- As Lock, *plus:* L l(m,b) //Lock; blocking if b TimedLock Concept ----------------- As Lock (not TryLock), *plus:* L l(m,t) //Blocking lock, failing if not obtained by time t //If t == 0, acts as TryLock. Comments and criticism welcome, Christopher