From f1149cdcfdf02aee5bfce8f55a97d51e0196f2e3 Mon Sep 17 00:00:00 2001
From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Date: Sun, 8 Dec 2019 19:40:53 +0100
Subject: [PATCH] fiber: unref fiber.storage via global Lua state
Fiber.storage is a table, available from anywhere in the fiber. It
is destroyed after fiber function is finished. That provides a
reliable fiber-local storage, similar to thread-local in C/C++.
But there is a problem that the storage may be created via one
struct lua_State, and destroyed via another. Here is an example:
function test_storage()
fiber.self().storage.key = 100
end
box.schema.func.create('test_storage')
_ = fiber.create(function()
box.func.test_storage:call()
end)
There are 3 struct lua_State:
tarantool_L - global always alive state;
L1 - Lua coroutine of the fiber, created by fiber.create();
L2 - Lua coroutine created by that fiber to execute
test_storage().
Fiber.storage is created on stack of L2 and referenced by global
LUA_REGISTRYINDEX. Then it is unreferenced from L1 when the fiber
is being destroyed.
That is generally ok as soon as the storage object is always in
LUA_REGISTRYINDEX, which is shared by all Lua states.
But soon during destruction of the fiber.storage there will be
only tarantool_L and the original L2. Original L2 may be already
deleted by the time the storage is being destroyed. So this patch
makes unref of the storage via reliable tarantool_L.
Needed for #4662
(cherry picked from commit 5b3e8a721d6c61501498f770d0460c46aab5e792)
---
src/lua/fiber.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/lua/fiber.c b/src/lua/fiber.c
index 124908a059..b137b27d26 100644
--- a/src/lua/fiber.c
+++ b/src/lua/fiber.c
@@ -368,7 +368,7 @@ lua_fiber_run_f(MAYBE_UNUSED va_list ap)
/* Destroy local storage */
int storage_ref = f->storage.lua.ref;
if (storage_ref > 0)
- luaL_unref(L, LUA_REGISTRYINDEX, storage_ref);
+ luaL_unref(tarantool_L, LUA_REGISTRYINDEX, storage_ref);
/*
* If fiber is not joinable
* We can unref child stack here,
--
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