Lua 创建和使用协程
示例
与协程互动的所有功能在协程表中都可用。通过使用带有单个参数的coroutine.create函数来创建新的协程：一个具有要执行的代码的函数：
thread1 = coroutine.create(function()
print("honk")
end)
print(thread1)
-->> thread: 6b028b8c协程对象返回代表新协程的thread类型的值。创建新的协程时，其初始状态将被暂停：
print(coroutine.status(thread1)) -->> suspended
要恢复或启动协程，函数和coroutine.resume时，给定的第一个参数是线程对象：
coroutine.resume(thread1) -->> honk
现在协程执行代码并终止，将其状态更改为dead，至此无法恢复。
print(coroutine.status(thread1)) -->> dead
Coroutinescansuspenditsexecutionandresumeitlaterthankstothecoroutine.yieldfunction:
thread2 = coroutine.create(function()
for n = 1, 5 do
print("honk "..n)
coroutine.yield()
end
end)Asyoucansee,coroutine.yield()ispresentinsidetheforloop,nowwhenweresumethecoroutine,itwillexecutethecodeuntilitreachsacoroutine.yield:
coroutine.resume(thread2) -->> honk 1 coroutine.resume(thread2) -->> honk 2
Afterfinishingtheloop,thethreadstatusbecomesdeadandcannotberesumed.Coroutinesalsoallowstheexchangebetweendata:
thread3 = coroutine.create(function(complement)
print("honk "..complement)
coroutine.yield()
print("再次鸣喇叭 "..complement)
end)
coroutine.resume(thread3, "stackoverflow")
-->> honk stackoverflowIfthecoroutineisexecutedagainwithnoextraarguments,thecomplementwillstill theargumentfromthefirstresume,inthiscase"stackoverflow":
coroutine.resume(thread3) -->> 再次鸣喇叭 stackoverflow
Finally,whenacoroutineends,anyvaluesreturnedbyitsfunctiongotothecorrespondingresume:
thread4 = coroutine.create(function(a, b)
local c = a+b
coroutine.yield()
return c
end)
coroutine.resume(thread4, 1, 2)
print(coroutine.resume(thread4))
-->> true, 3Coroutinesareusedinthisfunctiontopassvaluesbacktoacallingthreadfromdeepwithinarecursivecall.
local function Combinations(l, r)
local ll = #l
r = r or ll
local sel = {}
local function rhelper(depth, last)
depth = depth or 1
last = last or 1
if depth > r then
coroutine.yield(sel)
else
for i = last, ll - (r - depth) do
sel[depth] = l[i]
rhelper(depth+1, i+1)
end
end
end
return coroutine.wrap(rhelper)
end
for v in Combinations({1, 2, 3}, 2) do
print("{"..table.concat(v, ", ").."}")
end
--> {1, 2}
--> {1, 3}
--> {2, 3}协程也可以用于延迟评估。
-- slices a generator 'c' taking every 'step'th output from the generator
-- starting at the 'start'th output to the 'stop'th output
function slice(c, start, step, stop)
local _
return coroutine.wrap(function()
for i = 1, start-1 do
_ = c()
end
for i = start, stop do
if (i - start) % step == 0 then
coroutine.yield(c())
else
_ = c()
end
end
end)
end
local alphabet = {}
for c = string.byte('a'), string.byte('z') do
alphabet[#alphabet+1] = string.char(c)
end
-- only yields combinations 100 through 102
-- requires evaluating the first 100 combinations, but not the next 5311633
local s = slice(Combinations(alphabet, 10), 100, 1, 102)
for i in s do
print(table.concat(i))
end
--> abcdefghpr
--> abcdefghps
--> abcdefghpt协程可用于如Lua编程中所述的管道构造。PiL的作者RobertoIerusalimschy也发表了一篇论文，内容涉及使用协程来实现更高级的通用流程控制机制，例如延续。