Re: Per-value metatables would be great for threads
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- Subject: Re: Per-value metatables would be great for threads
- From: Philipp Janda <siffiejoe@...>
- Date: 2015年8月28日 11:23:02 +0200
Am 28.08.2015 um 09:48 schröbte Dirk Laurie:
Was there near-universal acclaim for per-value metatables,
or am I just remembering what I like to? Anyway, pointing out
one more advantage can't hurt :-)
When a coroutine goes dead, there is often some finalizing to do.
Setting a return hook in order to call a finalizer looks kludgy.
The neat way is a __gc metamethod.
Two ways of calling finalizers for coroutines in Lua 5.2+ without hooks:
local function mycocreate1( func, gc )
local fin = setmetatable( { thread = false }, { __gc = gc } )
local t = coroutine.create( function( ... )
local finalizer = fin -- keep finalizer as an upvalue
return func( ... )
end )
fin.thread = t
return t
end
local threadgcs = setmetatable( {}, { __mode = "k" } )
local function mycocreate2( func, gc )
local t = coroutine.create( func )
threadgcs[ t ] = setmetatable( { thread = t }, { __gc = gc } )
return t
end
local function gc( t )
print( t.thread )
end
do
local t1 = mycocreate1( function() end, gc )
local t2 = mycocreate2( function() end, gc )
collectgarbage() collectgarbage()
print( "xxx" )
end
collectgarbage() collectgarbage()
print( "yyy" )
That said, coroutines are GCObjects already, and a fresh coroutine costs
about 1K of memory, so the extra 8 bytes for a metatable pointer doesn't
really hurt.
Philipp