Howard Hinnant wrote:
On Jul 7, 2004, at 9:19 AM, Michael Glassford wrote:
There are still the constructor issues to deal with in such a lock taxonomy, however. The main one: how do you define destructors that are consistent within a lock concept and also consistent between concepts. E.g., on the one hand it seems that a one-parameter constructor should do the same thing in all lock types--so it would have to block; on the other hand, it seems that TryLock constructors should not block unless instructed to do otherwise.
Agreed, and I think the scoped_try_lock got it wrong (i.e. scoped_try_lock(mut) should block).
I've come to agree with you on this, and hope to fix it one way or another (see other replies in this discussion).
This somewhat irritates me as I have coded and shipped Metrowerks::scoped_try_lock with the wrong semantics (doesn't block). :-\
I'm finding more and more uses for generic lock code.
I'm glad to know this; I wondered at first whether generic uses of locks would be at all common or important.
The generic helper I showed yesterday was one. Another is:
template <class TryLock1, class TryLock2> class lock_both { public:
lock_both(TryLock1& m1, TryLock2& m2, bool lock_it = true);
~lock_both();
void lock(); bool try_lock(); void unlock(); bool locked() const; operator int bool_type::* () const;
private: lock_both(const lock_both&); lock_both& operator=(const lock_both&); };
which allows you to lock two locks without fear of deadlock. So consistent syntax/semantics across lock types is a real win.
Agreed. I always like as much consistency as possible, which is why I started the whole lock constructor discussion. Mike