BIND 10 #2850: Define and implement ZoneTableSegmentMapped

[BIND 10 Development]

#2850: Define and implement ZoneTableSegmentMapped
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |  jinmei
            Priority:  medium        |                       Status:
           Component:  data source   |  reviewing
            Keywords:                |                    Milestone:
           Sensitive:  0             |  Sprint-20130514
         Sub-Project:  DNS           |                   Resolution:
Estimated Difficulty:  5             |                 CVSS Scoring:
         Total Hours:  0             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |  shared memory data source
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by jinmei):

 Replying to [comment:21 muks]:

 > > one more note: I've noticed another issue with
 > > `MemorySegmentMapped::setNamedAddress(Impl)`.  If the underlying
 > > segment grows inside this method, the given pointer can be invalidated
 > > by the time the storage is allocated.
 >
 > Isn't this the same reason why we allocate the name with `NULL` address
 first, and repeat it with the real address after allocation? Or is it some
 other issue?

 It's essentially the same problem, but at that time we (or at least I)
 mainly were concerned that we might have to re-get the address as the
 mapped address may change before and after the call to
 `setNamedAddress`.  The above issue is more about `setNamedAddress`
 internal.  For example, even if the caller simply calls
 `setNamedAddress` and then closes the segment, it's still problematic,
 because `addr` may be invalidated if `find_or_construct()` requires
 retry:

 {{{#!cpp
         offset_ptr<void>* storage =
             impl_->base_sgmt_->find_or_construct<offset_ptr<void> >(
                 name, std::nothrow)();
         if (storage) {
             *storage = addr;
             return (grown);
         }
 }}}

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Ticket URL: <http://bind10.isc.org/ticket/2850#comment:23>
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