One very easy way to lock a block is to just keep a pointer to that block (blocks won't be freed if a pointer to them exists). If you only need to lock it within the lifetime of a function, then just keep a pointer on the stack (ie a local variable). Otherwise, use a global variable to store the pointer. Then either set that variable to NULL when you're done with the block (and it'll be freed during the next collection), or call gc_free on that pointer (and also set the pointer to NULL if it's a global variable).

what if say I have an array which has pointers to other objects, I would have to keep those on the stack too, right ? if I understand correctly, the only other way to do this is to add another bit to mark the object as locked ?

No, those other objects are pointed to (by the array), and so will remain "locked", so to speak.

Really you don't need to worry about this. The beauty of a GC is that you don't have to worry about memory management. You just allocate memory, and as long as a pointer to that memory exists somewhere, it'll remain valid memory.

you know this issue is actually related to the realloc issue, I only ask about this because I was realloc'ing memory to a dynamic array and at some point it returned NULL, which made me think that GC collected the memory.. I will close this one now. Thanks!

I'm curios about this too. Can GC move allocated and locked blocks (to
defragment the heap) and keep the pointers valid? That'd require a virtual
/ physical manager, I'd guess.

On Thu, Feb 27, 2014 at 10:20 AM, Damien George notifications@github.comwrote:

No, those other objects are pointed to (by the array), and so will remain
"locked", so to speak.

Really you don't need to worry about this. The beauty of a GC is that you
don't have to worry about memory management. You just allocate memory, and
as long as a pointer to that memory exists somewhere, it'll remain valid
memory.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/326#issuecomment-36190672
.

Meski

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@meski issue #322 is more related I think...

Can GC move allocated and locked blocks (to defragment the heap) and keep the pointers valid?

No. It's a conservative GC, so it cannot do relocations/compacting. It would require some work to make it an exact GC: all pointers that exist in C would have to be treated specially, since at any point they can change.