A handle is a method of indirection. Why the concern about
which heap the actual data is in as long as the handle remains
the same?
That is to say that the implementation of a handle may change,
the handle represents nothing but the promise to locate your
memory when you call for it (with MemHandleLock). MemResizeHandle
can not now, nor ever, change the handle but it -may- change the location
of the memory that the handle refers to ... but why would that change be
of any concern? As long as the -handle- remains unchanged after
a call to MemHandleResize -- and it will -- shouldn't that be good enough?
-rmh
Shannon wrote in message <5044@palm-dev-forum>...
You are right that MemHandleResize will not change the handle.
In OS 2.0 and earlier, heap sizes were a max of 64K, and could have lots of
stuff in them. It was often that a MemHandleResize of a database handle
would fail, requiring it to be re-allocated in another heap. Doing what you
are describing should work fine in all current post-OS 2.0 implementations,
but what about the future?
I am considering only supporting OS 3.5 and above with new software, and I
want to know if I can greatly simplify my memory management schemes in the
future. One way would be to do as you describe, only using MemHandeResize on
memory handles.
But, I need a call from Palm to make sure they never go back to a multiple
heap data architecture. For example, would they consider doing multiple
heaps in whatever they intend to do with Nokia, or any other OS's they have
planned? Is this a chip dependent thing? It would be great if we could get a
commitment to only have one data heap in the OS.
In answer to your last question, DmResizeRecord simply calls MemHandleResize
in post 2.0 implementations currently. But again, what about the future?
Shannon
>We use handles to create multiple of indices for a database. However we
always use MemHandleResize. The declaration as par the API docs is
>
>Err MemHandleResize (VoidHandle h, ULong newSize)
>
>As you can see h is not a pointer to a handle, there is no way the function
could change the value of h and return it. So, I assumed MemHandleResize
never changes a handle. Where as DmResizeRecord returns a handle. Chances
are there, that it will be different than the one I passed. Till now I have
not faced any problems with this scheme.
>
>I understand this restricts us to one heap only. But, this is the best
index referrence, we could think of. Record positions need to be updated
constantly, and unique IDs involves a linear search.
>
>On a final note, the API docs say
>"On devices running version 2.0 or earlier of Palm OS � , the
>MemHandleResize function tries to resize the chunk only within
>the same heap, whereas DmResizeRecord will look for space in
>other data heaps if it cannot find enough space in the original heap."
>
>So, what happens in devices running version 3.0 or later of Palm OS?
>
>-Sugho-
>
>>From: Shannon <[EMAIL PROTECTED]>
>>Reply-To: "Palm Developer Forum" <[EMAIL PROTECTED]>
>>To: "Palm Developer Forum" <[EMAIL PROTECTED]>
>>Subject: Can Palm comment on the future of heaps?
>>Date: Wed, 15 Mar 2000 08:07:33 -0800
>>
>>Currently, the API specifies that whenever a storage handle gets resized,
like through a DmResizeRecord, or a MemHandleResize, the handle might get
relocated into a different data heap.
>>
>>However, since OS 3.0, there has only been one data heap, so that storage
handles will not get moved when resized. The latest doc makes an offhand
reference to this in the description of MemHandleResize.
>>
>>Can we count on this behavior in the future? In other words, will
DmResizeRecord ALWAYS return the same handle in future OS's?
>>
>>It would be a huge advantage if we could count on non-moving data handles.
One thing we could do with it is make multiple indexes into a database when
an application starts up, and be able to count on the handles not changing
while the application is running.
>>
>>Any comment from Palm?
>>
>>Shannon
>>
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>>Hands High Software
>>Award winning software for the Palm(tm) Computing platform
>>
>><http://www.handshigh.com/>
>>
>>[EMAIL PROTECTED]
>>
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>>--
>>For information on using the Palm Developer Forums, or to unsubscribe,
please see http://www.palm.com/devzone/mailinglists.html
>>
>
>______________________________________________________
>Get Your Private, Free Email at http://www.hotmail.com
>
>
>--
>For information on using the Palm Developer Forums, or to unsubscribe,
please see http://www.palm.com/devzone/mailinglists.html
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hands High Software
Award winning software for the Palm(tm) Computing platform
<http://www.handshigh.com/>
[EMAIL PROTECTED]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
For information on using the Palm Developer Forums, or to unsubscribe, please see
http://www.palm.com/devzone/mailinglists.html
