Fibers collected by gc even if they still alive

fibergc.lua

#!/usr/bin/env tarantool
print(_G._TARANTOOL)

-- box.cfg{}
require 'jit.dump'.start("hotloop=1")

local fiber = require 'fiber'
local log = require 'log'
local json = require 'json'
json.cfg{ encode_use_tostring = true }

local function gc()
	collectgarbage('collect')
	collectgarbage('collect')
end

local registry = setmetatable({}, { __mode = 'v' })
local id = 0

local evaluate
local setgc = function(f)
	f = f or fiber.self()
	debug.getmetatable(f).__gc = function(me)
		print("__gc called for ", pcall(tostring, me))
	end
end

local function runit(sleep)
	id = id + 1
	local udata = fiber.create(evaluate, sleep)
	registry[tostring(id)] = udata
	gc()
	log.info(json.encode(registry))
end

function evaluate(sleep)
	local me = fiber.self()
	setgc()
	log.info("Started", fiber.id())
	fiber.sleep(sleep)
	log.info("Finished %s", fiber.id())
	return
end

for _ = 1, 5 do
	runit(1+math.random()+math.random(0,1))
end

fiber.create(function()
	fiber.name("watcher")
	while true do
		log.info("watcher", json.encode(registry))
		fiber.sleep(0.5)
		gc()
	end
end)

2.6.1-11-g37077a48e
Started
{"1":{"status":"suspended","name":"lua","id":104}}
Started
{"1":{"status":"suspended","name":"lua","id":104},"2":{"status":"suspended","name":"lua","id":105}}
Started
{"2":{"status":"suspended","name":"lua","id":105},"1":{"status":"suspended","name":"lua","id":104},"3":{"status":"suspended","name":"lua","id":106}}
Started
{"2":{"status":"suspended","name":"lua","id":105},"4":{"status":"suspended","name":"lua","id":107},"1":{"status":"suspended","name":"lua","id":104},"3":{"status":"suspended","name":"lua","id":106}}
Started
{"4":{"status":"suspended","name":"lua","id":107},"1":{"status":"suspended","name":"lua","id":104},"5":{"status":"suspended","name":"lua","id":108},"2":{"status":"suspended","name":"lua","id":105},"3":{"status":"suspended","name":"lua","id":106}}
watcher
entering the event loop
watcher
watcher
watcher
watcher
Finished 106
Finished 107
Finished 108
watcher
Finished 105
Finished 104
watcher

I was expect to receive dump of registry inside watcher fiber when fibers were still alive

__gc is executed for each fiber after they really finished

1.10.6-53-gc1ae2bb88
Started
{"1":{"status":"suspended","name":"lua","id":102}}
Started
{"1":{"status":"suspended","name":"lua","id":102},"2":{"status":"suspended","name":"lua","id":103}}
Started
{"2":{"status":"suspended","name":"lua","id":103},"1":{"status":"suspended","name":"lua","id":102},"3":{"status":"suspended","name":"lua","id":104}}
Started
{"2":{"status":"suspended","name":"lua","id":103},"4":{"status":"suspended","name":"lua","id":105},"1":{"status":"suspended","name":"lua","id":102},"3":{"status":"suspended","name":"lua","id":104}}
Started
{"4":{"status":"suspended","name":"lua","id":105},"1":{"status":"suspended","name":"lua","id":102},"5":{"status":"suspended","name":"lua","id":106},"2":{"status":"suspended","name":"lua","id":103},"3":{"status":"suspended","name":"lua","id":104}}
watcher
entering the event loop
__gc called for 	true	fiber: 107
watcher
watcher
watcher
watcher
Finished 104
Finished 105
Finished 106
__gc called for 	false	the fiber is dead
__gc called for 	false	the fiber is dead
__gc called for 	false	the fiber is dead
watcher
Finished 103
Finished 102
__gc called for 	false	the fiber is dead
__gc called for 	false	the fiber is dead
watcher
watcher
watcher
watcher
watcher
watcher
watcher
watcher