On Wed, 2 May 2018, Tuzun, Robert wrote:
Suppose a user of the class wanted to set or retrieve element n. This could be done by setting or retrieving bit n%8 of Bytes[n/8]. From the previous email's remarks about race conditions, this would be thread-safe, correct, even when writing to?
Nope. This is basically how vector<bool> already works under the hood. The race condition happens when trying to set or retrieve that bit: you look at the current byte, you OR that bit to 1, and you write the result, right? Nope. Because if *another* thread tries to do the same thing, and both look at the current byte at the same time, then neither thread gets the set-to-1 version from the other thread, and only one or the other write actually occurs. There's probably some std::atomic way to fix this but nothing I'd feel safe trying to futz with, and even a perfect fix would necessarily ruin caching and thus speed. --- Roy ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Libmesh-devel mailing list Libmesh-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-devel
