From 54fe3def54132bf739f38cd77ad78a73aa6ad23b Mon Sep 17 00:00:00 2001
From: Daniel Silverstone <daniel.silverstone@codethink.co.uk>
Date: Mon, 13 Aug 2012 17:33:24 +0100
Subject: OBJECTS: Refcount tags (proxies) so that we only pass __gc across
 when we really mean it

---
 lib/supple/objects.lua | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/lib/supple/objects.lua b/lib/supple/objects.lua
index 72eaf9a..2f5da79 100644
--- a/lib/supple/objects.lua
+++ b/lib/supple/objects.lua
@@ -16,18 +16,18 @@ local track = require 'supple.track'
 
 local my_objects_by_obj = {}
 local my_objects_by_tag = {}
+local my_objects_expn_by_tag = {}
 local my_name = "UNSET"
 local my_counter = 0
 local their_objects_by_tag = setmetatable({}, { __mode="v" })
 local their_objects_by_obj = setmetatable({}, { __mode="k" })
+local their_objects_refcnt = {}
 local proc_call = nil
 
 local type = capi.rawtype
 
 local function clean_down(call_other_end)
    track.enter("clean_down")
-   setmetatable(their_objects_by_tag, { __mode="v" })
-   setmetatable(their_objects_by_obj, { __mode="k" })
    -- And force a full GC
    gc "collect"
    gc "collect"
@@ -39,6 +39,7 @@ local function clean_down(call_other_end)
    -- And forget all our local objects
    my_objects_by_obj = {}
    my_objects_by_tag = {}
+   my_objects_expn_by_tag = {}
    track.leave("clean_down")
 end
 
@@ -92,13 +93,14 @@ local function give(obj, special_tag)
    local tag = my_objects_by_obj[obj]
    if tag then
       track.leave("give", "ours", tag)
-      return { tag = tag }
+      return my_objects_expn_by_tag[tag]
    end
    -- otherwise wrap it freshly for us and return that.
    local tag = new_tag(special_tag)
    local expn = capi.explain(obj, tag)
    my_objects_by_obj[obj] = tag
    my_objects_by_tag[tag] = obj
+   my_objects_expn_by_tag[tag] = expn
    track.leave("give", "ours, new", tag)
    return expn
 end
@@ -131,9 +133,9 @@ local function receive(obj)
    assert(capi.type(proxy) == obj.type)
    their_objects_by_tag[tag] = proxy
    their_objects_by_obj[proxy] = tag
+   their_objects_refcnt[tag] = (their_objects_refcnt[tag] or 0) + 1
    -- Fill out the metatable
    obj.methods = obj.methods or {}
-   obj.methods[#obj.methods+1] = "__gc"
    if obj.type == "function" then
       obj.methods[#obj.methods+1] = "__call"
    end
@@ -152,6 +154,13 @@ local function receive(obj)
       end
       mt[name] = meta_func
    end
+   function mt:__gc()
+      their_objects_refcnt[tag] = their_objects_refcnt[tag] - 1
+      if their_objects_refcnt[tag] == 0 then
+	 their_objects_refcnt[tag] = nil
+	 proc_call(tag, "__gc")
+      end
+   end
    -- And return the proxy object
    track.leave("receive", "theirs, new", tostring(proxy))
    return proxy
@@ -163,6 +172,7 @@ local function forget_mine(tag)
    assert(obj, "Trying to forget nil object: " .. tag)
    my_objects_by_tag[tag] = nil
    my_objects_by_obj[obj] = nil
+   my_objects_expn_by_tag[tag] = nil
    track.leave("forget_mine", tag)
 end
 
-- 
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