bugfix: leaked ctxs slot when ngx_lua_ffi_set_ctx_ref failed.

ref_in_table() reserves a slot in the shared ctxs table before the FFI
call. When ngx_http_lua_ffi_set_ctx_ref() returned non-FFI_OK (OOM
registering the request-pool cleanup), the slot was never released and
accumulated until the worker exited.

- get_ctx_table(): release the slot before returning nil.

- set_ctx_table(): the return value of the FFI call was ignored; now
  release the slot and raise "no memory", matching the C-side
  luaL_error(L, "no memory") convention.

Add base.unref_in_table() as the public counterpart to base.ref_in_table()
that pushes the ref onto the free list at FREE_LIST_REF, mirroring the
layout used by luaL_ref/luaL_unref on the C side (both operate on the
same table via the ngx_lua_ctx_tables registry key).

Author: zhuizhuhaomeng

lib/resty/core/base.lua

@@ -222,6 +222,16 @@ function _M.ref_in_table(tb, key)
 end
 
 
+-- Release a slot acquired via ref_in_table() back to the free list.
+-- Mirrors the layout used by luaL_ref / luaL_unref on the C side (both
+-- use the slot at FREE_LIST_REF as the free-list head), so tables shared
+-- with luaL_ref/unref (e.g. ngx_lua_ctx_tables) stay consistent.
+function _M.unref_in_table(tb, ref)
+    tb[ref] = tb[FREE_LIST_REF]
+    tb[FREE_LIST_REF] = ref
+end
+
+
 function _M.allows_subsystem(...)
     local total = select("#", ...)
 

lib/resty/core/ctx.lua

@@ -13,6 +13,7 @@ local register_setter = misc.register_ngx_magic_key_setter
 local registry = debug.getregistry()
 local new_tab = base.new_tab
 local ref_in_table = base.ref_in_table
+local unref_in_table = base.unref_in_table
 local get_request = base.get_request
 local FFI_NO_REQ_CTX = base.FFI_NO_REQ_CTX
 local FFI_OK = base.FFI_OK
@@ -106,6 +107,7 @@ do
 
             ctx_ref = ref_in_table(ctxs, ctx)
             if ngx_lua_ffi_set_ctx_ref(r, ctx_ref) ~= FFI_OK then
+                unref_in_table(ctxs, ctx_ref)
                 return nil
             end
             return ctx
@@ -136,7 +138,10 @@ local function set_ctx_table(ctx)
 
     if ctx_ref < 0 then
         ctx_ref = ref_in_table(ctxs, ctx)
-        ngx_lua_ffi_set_ctx_ref(r, ctx_ref)
+        if ngx_lua_ffi_set_ctx_ref(r, ctx_ref) ~= FFI_OK then
+            unref_in_table(ctxs, ctx_ref)
+            error("no memory")
+        end
         return
     end
     ctxs[ctx_ref] = ctx