Author: Robert Hyatt
Date: 20:54:03 04/24/01
Go up one level in this thread
On April 24, 2001 at 22:44:22, Hristo wrote: >Thanks Eugene. >However this might be a bit complicated. >A simple case (example) is this: >variable A has to be protected by semaphore aC (multi threading) >variable B has to be protected by semaphore bC >at some point in your program you want to access both >A and B at the same time. How do you obtain a lock >on both of them (aC and bC)? >Well, you need to do aC.lock() and then bC.lock(). >This is simple, not!? What if another piece of your program >does first bC.lock() and then aC.lock()?! You are facing a chance >of being dead locked! Tighter than a drum. Poor design and a known issue. Always set the locks in the same order and this can't happen. If you set b, knowing you will eventually want to set a, either rewrite the code or set a followed by b, even though you are setting a well before it is needed. >Thread 1 just got a lock on aC, when thread 2 got a lock on bC, >and now both threads are waiting for the other thread to release ... >Nasty eh? >So you use WaitForMultipleObjects(...) and it makes sure that this >doesn't happen!!! Awesome! MS has gone a step further to actually >provide this functionality for whole range of system wide handles >that can be locked, signalled, flagged, etc ... Awesome functionality, >no doubt. And this is only a simple example! > >WaitForMultipleObjects can help your application to be faster, and more >maintainable. Unless you are willing to spend the time to design around >the problems when you do not have this functionality! As described, designing around it is a _good_ thing. That's a known issue in parallel programming, and mutually-exclusive-resource-management. I've never written code that would behave like that. Which is I guess why I have managed to never use such a thing. :) > >After all of this, I must admit that I despise M$ products, including all >Windowz and anything that runs on it! ;-) The only OS I use at home >is linux. It has been almost 4 years now that I haven't seen M$ at home. >Please, don't consider this a flame war ... or any of that nonsense ... >MS deserves credit in some areas, however this can not make me like them! > > >cheers. >hristo
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