15.12.2010, в 10:36, Stephan Aßmus написал(а): > The only thing one needs to watch out for is to declare such a boolean > volatile (which I believe this code does, if memory serves). Otherwise the > thread which polls the condition may read from a cached location and miss the > change. Worst that can happen on a hypothecial architecture where writing a > byte is not atomic is that the changed condition takes affect one loop cycle > later.
The behavior of volatile depends on the compiler - there is no guarantee that a memory barrier will be emitted. Historically, volatile existed not for multiprocessor systems, but for special addresses in address space (like memory mapped I/O), where it is important to actually access the address each time, and not than keep a local variable in a boolean. There is code in WebKit that doesn't care about the other thread immediately seeing the change of a boolean value, and just hopes that it will propagate soon enough in practice. I remember implementing worker thread termination in that way. This code is of course formally wrong. - WBR, Alexey Proskuryakov _______________________________________________ webkit-dev mailing list [email protected] http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
