readview: fix garbagecollector

Added workaround for garbagecollection of readview because
for tarantool lua (and lua 5.1) __gc metamethod only works for cdata types.

See tarantool/tarantool#5770

Author: better0fdead

crud/readview.lua

@@ -286,6 +286,15 @@ end
 function Readview_obj.create(vshard_router, opts)
     local readview = {}
     setmetatable(readview, Readview_obj)
+
+    -- For tarantool lua (and lua 5.1) __gc metamethod only works for cdata types.
+    -- So in order to create a proper GC hook, we need to create cdata with
+    -- __gc call.
+    -- __gc call for this cdata will be a __gc call for our readview.
+    -- https://github.com/tarantool/tarantool/issues/5770
+    local proxy = newproxy(true)
+    getmetatable(proxy).__gc = function(_) Readview_obj.__gc(readview) end
+
     readview._name = opts.name
     local results, err, err_uuid = vshard_router:map_callrw('_crud.readview_open_on_storage',
         {readview._name}, {timeout = opts.timeout})

test/integration/select_readview_test.lua

@@ -1,4 +1,5 @@
 local fio = require('fio')
+local fiber = require('fiber')
 
 local t = require('luatest')
 
@@ -187,14 +188,15 @@ pgroup.test_close_gc_on_router = function(g)
         collectgarbage("collect")
         collectgarbage("collect")
     ]])
+    fiber.sleep(1)
     t.assert_equals(err, nil)
     local res = {}
-    helpers.call_on_storages(g.cluster, function(server, replicaset, res)
+    helpers.call_on_storages(g.cluster, function(server)
         local instance_res = server.net_box:eval([[
         return box.read_view.list()]])
-        res[replicaset.alias] = instance_res
+        table.insert(res, instance_res)
      end, res)
-    t.assert_equals(res, {["s-1"] = {}, ["s-2"] = {}})
+     t.assert_equals(res, {{}, {}, {}, {}})
 
 end
 
@@ -209,12 +211,12 @@ pgroup.test_close = function(g)
     ]])
     t.assert_equals(err, nil)
     local res = {}
-    helpers.call_on_storages(g.cluster, function(server, replicaset, res)
+    helpers.call_on_storages(g.cluster, function(server)
         local instance_res = server.net_box:eval([[
         return box.read_view.list()]])
-        res[replicaset.alias] = instance_res
+        table.insert(res, instance_res)
      end, res)
-    t.assert_equals(res, {["s-1"] = {}, ["s-2"] = {}})
+     t.assert_equals(res, {{}, {}, {}, {}})
 
 end