Palm OS Programming, 2nd Edition

Using Memory Effectively

Here are some tips to help you use the Memory Manager efficiently in your code. First, we engage in the classic debate of whether to use pointers or handles. Next, we remind you to check allocations. We conclude this section with an axiom of ours: keep the heap small.

Deciding Whether to Use Pointers or Handles

It can often be unclear when it is appropriate to use pointers (nonrelocatable blocks) and when to use handles (relocatable blocks). Here are some rules:

Use a pointer when working with a block of memory that exists for only a short time.

Relocating is only necessary when the Memory Manager needs to allocate more memory. If you’ve got some code that allocates a block of memory, works with it, and then deallocates it, there’s no need for it to be relocatable (since there will be no allocations during the lifetime of the block).

Use a pointer for a block of memory that must remain locked for its lifetime.

For example, to set the label of a control at runtime requires a pointer. One way to store the label would be to allocate a handle, immediately lock it, and then keep it locked for the lifetime of the control. A better approach would be to go ahead and allocate a pointer. A relocatable block that’s always locked can’t be relocated, so it might as well have been nonrelocatable. Not only would there be slightly more code when using handles, the relocatable block would be locked in the middle of the heap, causing fragmentation. Pointers are all allocated ...