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The current synchronization point enforces certain restrictions which are hard to workaround in certain areas of the code. The fact that the critical code can only be called from the sync point itself is a problem for some callback-driven parts. The "show fd" command for example is fragile regarding this. Also it is expensive in terms of CPU usage because it wakes every other thread just to be sure all of them join to the rendez-vous point. It's a problem because the sleeping threads would not need to be woken up just to know they're doing nothing. Here we implement a different approach. We keep track of harmless threads, which are defined as those either doing nothing, or doing harmless things. The rendez-vous is used "for others" as a way for a thread to isolate itself. A thread then requests to be alone using thread_isolate() when approaching the dangerous area, and then waits until all other threads are either doing the same or are doing something harmless (typically polling). The function only returns once the thread is guaranteed to be alone, and the critical section is terminated using thread_release(). |
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