[Openmcl-devel] add-gc-hook / drain-termination-queue

[Gary Byers]

CCL::ADD-GC-HOOK isn't documented for a number of reasons; as you're
calling it, it doesn't do anything useful.

You could force the termination function for R-POINTER objects to run
on some arbirtary thread P by making that function use PROCESS-INTERRUPT
(e.g.,

(trivial-garbage:finalize r-pointer?(lambda () (process-interrupt p (lambda () (rf-unprotect-ptr ptr)))))
)

I don't know what problem you're having, but it's not clear that causing that
termination function to run on a different thread fixes anything.

On Fri, 6 Sep 2013, Carlos Ungil wrote:

> Hello,
> 
> to ensure that finalizers are run from the main thread, I'm doing the
> following:
> 
> (setq ccl:*enable-automatic-termination* nil)
> (ccl::add-gc-hook
> ?(let ((process ccl:*current-process*))
> ? ?(lambda ()
> ? ? ?(ccl:process-interrupt process #'ccl:drain-termination-queue)))
> ?:post-gc))
> 
> Is this a good idea? The fact that add-gc-hook is not exported makes me
> doubt...
> 
> The context is the following: RCL embeds R in Common Lisp (using CFFI, the
> rf-protect and rf-unprotect-ptr functions below are foreign functions). When
> I need to hold a foreign pointer in the lisp side I wrap it in an object: I
> "protect" it to prevent it from being garbage-collected in the R side and I
> set up a finalizer to "unprotect" it when it's no longer in use.?
> 
> (defun make-r-pointer (ptr)
> ? (let ((r-pointer (make-instance 'r-pointer :pointer ptr)))
> ? ? (rf-protect ptr)
> ? ? (trivial-garbage:finalize r-pointer?(lambda () (rf-unprotect-ptr ptr)))
> ? ? r-pointer))
> 
> However, a function triggering garbage collection like the following one
> crashes the program (because the protect and unprotect functions will run
> concurrently, I think).
> 
> (ql:quickload :rcl)
> (rcl:r-init)
> (reduce #'+ (loop repeat 10000 append (rcl:r "runif" 1)))
> 
> The workaround mentioned above seems to solve the problem, but I wonder if
> there might be some undesirable effects.?
> 
> I also tried to let the automatic termination enabled, forcing the finalizer
> to run?each time?from the main thread
> 
> ? ? (trivial-garbage:finalize r-pointer?(let
> ((process??ccl:*current-process*)) (lambda () (process-interrupt process
> #'rf-unprotect-ptr ptr))))
> 
> but I couldn't make it work (the program hangs).
> 
> Cheers,
> 
> Carlos
> 
> 
>