Lua编程示例（八）：生产者-消费者问题

这个问题是比较经典的啦，基本所有语言的多线程都会涉及到，但是没想到Lua的这个这么复杂 抓狂看了好长时间才算看明白，先上个逻辑图：

开始时调用消费者，当消费者需要值时，再调用生产者生产值，生产者生产值后停止，直到消费者再次请求。设计为消费者驱动的设计。

图画的不太好，可以先将Filter遮住，它是过滤器对两个程序之间传递的信息进行处理。去掉Filter逻辑就更清晰些了，就是两个“线程”（其实是两个协同程序）互相调用。resume回到yield处开始，支持嵌套，返回到栈顶的yield位置。yield是非阻塞的“线程同步”。这到有点像linux里的管道通信。

function receive(prod)

print("receive is called")

local status,value = coroutine.resume(prod)

return value

end

function send(x,prod)

print("send is called")

return coroutine.yield(x)

end

function producer()

return coroutine.create(function ()

print("producer is called")

while true do

print("producer run again")

local x = io.read()

send(x)

end

end)

end

function filter(prod)

return coroutine.create(function ()

for line = 1,1000 do

print("enter fliter "..line)

local x = receive(prod)

print("receive in filter finished")

x= string.format("%5d %s",line,x)

send(x,prod)

end

end)

end

function consumer(prod)

print("consumer is called")

while true do

print("consumer run again")

local x = receive(prod)

print("retrun customer")

io.write(x,"n")

end

end

p = producer()

f=filter(p)

consumer(f)

运行结果：

consumer is called

consumer run again

receive is called

enter fliter 1

receive is called

producer is called

producer run again

fsy

send is called

receive in filter finished

send is called

retrun customer

1 fsy

consumer run again

receive is called

enter fliter 2

receive is called

producer run again

gaga

send is called

receive in filter finished

send is called

retrun customer

2 gaga

consumer run again

receive is called

enter fliter 3

receive is called

producer run again

......