[bind10-dev] some tips in using boost::offset_ptr

[JINMEI Tatuya / 神明達哉]

While playing with the prototype version of the scalable in-memory
design, I noticed "naive" (but intuitive) use of boost::offset_ptr
could affect performance pretty severely.

In the beginning I used this form of code a lot:

typedef offset_ptr<SomeStructure> SomeStructurePtr
for (SomeStructurePtr some = some_head; some; some = some->next) {
  // do something with "some"
}

The nice thing of this is it's quite compatible with the code using
normal pointers.  But in "some = some->next", we need to create a new
offset pointer object and calculate the new offset.  In performance
sensitive operation this can be significant.  (I've lost specific
numbers, but in my vague memory it could be 30-40% difference in
overall response performance).

So, while it's less intuitive, we need to do something like this in
performance sensitive code:

for (SomeStructure* some = some_head.get();
     some != NULL;
     some = some->next.get())

Or we can define "getNext()" method for SomeStructure to make it less
ugly:

for (SomeStructure* some = some_head.get();
     some != NULL;
     some = some->getNext())

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JINMEI, Tatuya