Is it possible to use Boehm garbage collector only for the part of the program?

Question

I've read article in LinuxJournal about Boehm-Demers-Weiser garbage collector library. I'm interesting to use it in my library instead of my own reference counting implementation.

I have only one question: is it possible to use gc only for my shared library and still use malloc/free in the main application? I'm not quite understand how gc checks the heap so I'm worrying about performance of gc in that case and possible side effects.

Answer 1

The example in the manual states:

It is usually best not to mix garbage-collected allocation with the system malloc-free. If you do, you need to be careful not to store pointers to the garbage-collected heap in memory allocated with the system malloc.

And more specifically for C++:

In the case of C++, you need to be especially careful not to store pointers to the garbage-collected heap in areas that are not traced by the collector. The collector includes some alternate interfaces to make that easier.

Looking at the source code in the manual you will see the garbage-collected memory is handled through specific calls, hence, the management is handled separately (either by the collector or manually). So as long your library handles its internals properly and doesn't expose collected memory, you should be fine. You don't know how other libraries manage their memory and you can use them as well, don't you? :)

Answer 2

I believe that yes, you can mix the two: however if you allocate an object with the normal allocator that holds a reference to an object you allocate with the garbage collecting one, then that reference will not be visible to the GC so that object may be prematurely deallocated.

Have a look at the GC_MALLOC_UNCOLLECTABLE function specification if you need the GC to take account of references in memory that shouldn't be collected.

In summary, yes, but here be dragons if you aren't careful!