Lua编程（八）协同程序的高级用法——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



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
......

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