Fix race condition in task state table unref

tests/main.lua

@@ -19,7 +19,7 @@ local icons = {
 }
 
 local function color(name, s)
-  return colors[name] .. s .. colors.reset
+  return ("%s %s %s"):format(colors[name], s, colors.reset)
 end
 
 local function create_test(name, f, group)
@@ -54,7 +54,7 @@ local function name_test(test)
   local name = test.name
   local group = test.group
   while group ~= nil do
-    if group.name ~= "" then name = string.format("%s %s %s", group.name, icons.chevron, name) end
+    if group.name ~= "" then name = ("%s %s %s"):format(group.name, icons.chevron, name) end
     group = group.parent
   end
   return name
@@ -68,11 +68,12 @@ local function run_test(test)
   local ok, res = xpcall(test.f, trace, test)
   if ok then
     test.state = "pass"
-    print("", string.format("%s %s", color("pass", "PASS"), name_test(test)))
+    print("", ("%s %s"):format(color("pass", "PASS"), name_test(test)))
   else
     test.state = "fail"
-    print("", string.format("%s %s\n\n%s\n", color("fail", "FAIL"), name_test(test), res))
+    print("", ("%s %s\n\n%s\n"):format(color("fail", "FAIL"), name_test(test), res))
   end
+  collectgarbage() -- gc after each test to test destructors
   return test
 end
 
@@ -86,6 +87,23 @@ local function start(cx, item)
   end
 end
 
+local function check_unrefs()
+  -- ensure all refs were properly unref'ed
+  local registry = debug.getregistry()
+  local count = #registry
+  local ref = 0 -- FREELIST_REF
+  while type(registry[ref]) == "number" do
+    local next = registry[ref]
+    registry[ref], ref = nil, next
+  end
+  for i = 1, count do
+    local value = registry[i]
+    if type(value) ~= "thread" then -- ignore threads pinned by the runtime
+      assert(rawequal(registry[i], nil), ("ref %d not unref'ed: %s"):format(i, registry[i]))
+    end
+  end
+end
+
 local function main(item)
   local cx = { tasks = {} }
   local pass, fail = 0, 0
@@ -97,17 +115,23 @@ local function main(item)
       fail = fail + 1
     end
   end
+  local code = 1
   if fail == 0 then
-    print("", color("pass", string.format("%s %d tests passed", icons.check, pass)))
-    return 0
+    print("", color("pass", ("%s %d tests passed"):format(icons.check, pass)))
+    code = 0
+  else
+    print(
+      "",
+      ("%s, %s"):format(
+        color("pass", ("%s %d tests passed"):format(icons.check, pass)),
+        color("fail", ("%s %d tests failed"):format(icons.cross, fail))
+      )
+    )
   end
-  print(
-    "",
-    color("pass", string.format("%s %d tests passed", icons.check, pass))
-      .. ", "
-      .. color("fail", string.format("%s %d tests failed", icons.cross, fail))
-  )
-  return 1 -- report error to cargo
+  cx = nil
+  collectgarbage()
+  check_unrefs()
+  return code -- report error to cargo
 end
 
 return main(create_group("", function()