<div class="gmail_quote">On Wed, Feb 10, 2010 at 1:30 PM, Walter Bright <span dir="ltr"><<a href="mailto:walter@digitalmars.com">walter@digitalmars.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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Robert Jacques wrote:<br>
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Yes. The reason I said that casting from local to shared was implementation defined was I knew the operation could be valid or invalid based on the type of GC used. However, your comment sounds like the standard C/C++ approach to thread-local allocation, which I discussed in the original post. In short, this model has been shown to be insufficient in C/C++ with regard to false sharing and has created several hacks to remove false sharing for identifiable hot-spots. Your comment also doesn't address the key challenge to D's GC, which is: where does the garbage returned to?<br>
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The garbage is returned to the global memory pool, not the local one. When the local ones run out, they go and get more from the global pool.</blockquote><div><br>Would it be practical for particular cache lines to have some kind of affinity for a given local allocator or for a cache line with both live and data and garbage to have an affinity for one of the thread pools that already owns an object within it?<br>
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(which I also discussed) Anyways, in order to prevent false sharing, small immutable objects need their own memory pool and shared objects need to be created in a different manner than local objects. To me this creates a logical separation of their memory pools and at a minimum requires the GC implementation to perform allocation using specific flags for each type qualifier.<br>
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False sharing isn't just a problem with shared objects, it happens with local objects. Using separate local pools to allocate from will minimize this problem.<div><div></div><div class="h5"><br>
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