Checkpoint and restore the heap in Ruby

Question

Ruby's callcc captures the current continuation, which can be subsequently called to restore the control, but not the data. I would like to capture the current continuation along with the current image of the memory.

It seems to me that capturing the heap shouldn't be very difficult; I can rely on ObjectSpace::each_object and ObjectSpace::dump_all, or Marshal.dump, or simply Object.clone. However, I don't see any straightforward way to restore the heap. Ideally, I would like to traverse the object_id -> object map, restoring the old image of the object for every object_id (and re-adding the object_id if the corresponding object had been GC'd). Unsurprisingly, there is no Ruby-level api that lets me do this. I am wondering if there are any low-level hooks to Ruby's GC that I can use.

Any help is appreciated, including suggestions about alternative approaches.

Answer 1

To answer my own question, Process.fork can be used to more-or-less achieve the effect of heap checkpointing and restoration. Whenever I have to checkpoint the heap, I fork a new process and let the child continue. The parent process now contains the checkpointed heap:

def checkpoint
  if Process.fork.nil? then # if child, then resume execution immediately
    return
  else # if parent, wait for the child to exit.
    Process.wait 
  end
  return # Parent now resumes execution from state it was in before forking.  
end

When state has to be restored, child process simply exits:

def restore
  Process.exit
end

I am currently using this solution, and haven't encountered any problems so far. I will edit this answer if I find any in the future.