Re: Making FFI callbacks call free() automatically when it's collected
- From: Johnson Lin <arch.jslin@xxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Fri, 20 Jul 2012 11:39:03 +0800
2012/7/20 Robert G. Jakabosky <bobby@xxxxxxxxxxxxxxx>:
> On Thursday 19, Johnson Lin wrote:
>> 2012/7/19 Mike Pall <mike-1207@xxxxxxxxxx>:
> If the C callback has a related userdata value (void *) then you can create
> one FFI callback instance for each C callback prototype and pass a callback id
> as the userdata value. The id would be used to lookup the Lua callback
> function in a table. Since the FFI callback slots are a limited resource this
> would help decrease the number of slots needed.
>
> local button_callbacks = {}
> local function wrapped_button_cb(event, ud)
> local id = tonumber(ffi.cast("uintptr_t", ud))
> local cb = button_callbacks[id]
> if cb then return cb(event, id) end
> end
> local button_cb = ffi.new("ButtonCB", wrapped_button_cb)
>
> local function wrap_button_cb(func)
> local id = #button_callbacks+1
> local ud = ffi.cast("uintptr_t", id)
> button_callbacks[id] = func
> return button_cb, ud
> end
>
>
> For UI callbacks it might be possible to do the callback lookup via a widget
> id or the widget's cdata value.
>
> --
> Robert G. Jakabosky
>
Yes, thanks for the suggestion. I now just use:
local function cdata_addr(cd) return tonumber(ffi.cast("int", cd)) end
to produce the address' value, and use that as the key internally, to
avoid the problem of cdata objects not suitable as the key directly.
best,
Johnson
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