Peter Dimov wrote:
In my opinion, we only need to do one version, and do it right.
I am not yet convinced. Altough Wikipedia is not a citable resource: http://en.wikipedia.org/wiki/Readers-writers_problem Butenhof's example in "Programming with Posix Threads". Bill Kempfs Implementation. Several sites I looked up in the net. I really would like to ask: How is the problem teached in schools? E.g. in an operating systems course?
The problem in this case is that a rwlock is almost purely a performance optimization. It is generally not used for its semantics (although I can imagine a few use cases for them); a mutex is replaced with a rwlock in an attempt to increase reader performance, preferably without slowing down writers to a standstill.
??? Sorry I absolutely cannot understand the previous. A pure performance optimization? I always thought it was mainly used because of its semantics: You are letting multiple readers access at the same time: This is the main source of performance gain. Of course, if you are measuring threads, that do no operations while holding the lock, you will measure the price of the lock implementation. However if you are doing substantial calculation while holding the lock I am almsot sure that this will be a win, even with the "emulated" rw-lock.
Viewed in this light, a read/write mutex that is slower than an ordinary mutex for the typical use cases is - IMO - not really worth having in the library.
I am still not convinced. What are the typical cases? Couild you possibly come up with examples?
We've never wanted a broken version of any component in any release. :-)
Ok second vote to remove it. (Mine first. ;-) Roland