Why the need for closure factory in Lua nginx module?

sunzoomass · 2018-02-27T16:47:08+00:00

Hi!The new flamegraph seems the memory allocation path is healthy.> Sadly it didn't fix it. My fix started segfault and worker are restarting so I am...

Why the need for closure factory in Lua nginx module?

sunzoomass

Hello openresty world,

I have a question around the idea of using closure factory for user scripts in the Lua nginx module.

Current design is to wrap the user script in a closure factory and store this compiled closure factory in a cache table.

lua_load() is performed on "return function() ...user script... end"

When the http request triggers Lua module, the cache table is looked and a lua_pcall() is made on the above which basically returns a function to be executed. Now the lua module calls lua_resume() to execute the user script.

My question is: what do we loose if we do not wrap the user script in the closure factory i.e.

lua_load/luaL_loadstring is performed on "...user script..."

and we store the returned function of lua_load/luaL_loadstring in the cache table.

When http request triggers Lua module, the cache table is looked up and the function over user script is returned without a need to perform lua_pcall().

What is the difference between the two approaches in the context of the Lua module?

Thanks in advance for clarifications.

Best,

Suraj

qleex001

Consider the environment of the closure. Without the closure factory, all coroutines would use the one closure and one environment.

If declared a global variable in a coroutine, all the other coroutines would been affected.

This is the reason, I think.

在 2018年2月27日星期二 UTC+8下午4:47:08，Suraj J写道：

Hello openresty world,

I have a question around the idea of using closure factory for user scripts in the Lua nginx module.

Current design is to wrap the user script in a closure factory and store this compiled closure factory in a cache table.
lua_load() is performed on "return function() ...user script... end"

When the http request triggers Lua module, the cache table is looked and a lua_pcall() is made on the above which basically returns a function to be executed. Now the lua module calls lua_resume() to execute the user script.

My question is: what do we loose if we do not wrap the user script in the closure factory i.e.
lua_load/luaL_loadstring is performed on "...user script..."
and we store the returned function of lua_load/luaL_loadstring in the cache table.
When http request triggers Lua module, the cache table is looked up and the function over user script is returned without a need to perform lua_pcall().

What is the difference between the two approaches in the context of the Lua module?

Thanks in advance for clarifications.

Best,
Suraj