Peter Dimov wrote: [...]
The mutex::timed_lock situation is a bit more complicated. POSIX labels pthread_mutex_timedlock as part of the Timeouts option, and I don't know whether this is because many implementations deliberatley do not provide timed locks, or because this is a relatively new addition to pthreads. Does someone know?
< Forward Quoted > David Butenhof wrote:
Alexander Terekhov wrote:
Pls read the message attached below. Perhaps you can answer the POSIX related (and also "thinking severals years ahead") question (to the newsgroup/list or to me -- I'll forward it then). I mean
The mutex::timed_lock situation is a bit more complicated. POSIX labels pthread_mutex_timedlock as part of the Timeouts option, and I don't know whether this is because many implementations deliberatley do not provide timed locks, or because this is a relatively new addition to pthreads.
Mutex timeout was devised for the "More realtime extensions" amendment, 1003.1d-1999. It's an option that is not required by the base standard or any profile (e.g., SUS), and that obviously was not in UNIX 98. I expect it is not widely implemented, nor to be a very high priority. (It's not in Tru64 or HP-UX, for example.)
In general, timed mutex operations are of relatively little use to general purpose applications in the first place. It's usually pretty hard to recover any shared data that may be corrupted because of unknown "bad behavior" on the part of the thread that failed to release the mutex. Because it's locked, you can't even unlock it, or reinitialize it; so you need to be able to dynamically switch to another mutex to continue operation. (As well as worrying about what the nonresponsive thread might be doing to your data.) As a result, there's usually not much you can do other than dump core in many cases. There are, of course, exceptions; but that's part of why the implementation priority has been relatively low on most systems.
This really was a feature desired by and intended for the truly "hard realtime" embedded system people, specifically for flight control systems and such that have no choice but to do "whatever is necessary".
(By the way, I've had this reply sitting in a buffer for days now, and just rediscovered it, entirely by coincidence, under a bunch of other windows. I've been having a lot of meetings and "stuff" lately, and this isn't the first time I've completely lost track of some message. Sorry. ;-) )
regards, alexander.