Author: Bruce Moreland
Date: 07:34:49 04/07/99
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On April 07, 1999 at 01:29:30, James Robertson wrote: >Just out of curiosity, how does a critical_section do this? Is it something >built into Windows? I don't know how they work. I know that when you try to lock a critical section it will efficiently wait if the critical section is busy, but that the whole general concept is kind of expensive, meaning that it is not something you want to be doing every node. You can implement critical sections yourself via assembly code. There are instructions like "cmpxchg", and instruction prefixes like "lock". If you are trying to control access to a fairly uncommon piece of code (a few times per second), a critical section is great. If you use the piece of code more often than this, you still may have a hard time beating a critical section, I think, but you might wish you could. There are other primitives which are useful with threads. You can create an "event" object, and you can tell a thread to wait until the event is triggered. While it's waiting it will sit there in an efficient state. There are semaphores but I haven't had reason to use those yet. Mutexes seem to be heavy-duty things that you'd use to keep different *processes* from accessing a resource simultaneously. That sounds pretty expensive. I don't know what I'm talking about, so if someone wants to correct me that would be fine. bruce
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